Document and Entity Information - shares shares in Millions	6 Months Ended
Document and Entity Information - shares shares in Millions	Jul. 03, 2016	Jul. 22, 2016
Document and Entity Information [Abstract]
Entity Registrant Name	Illumina Inc
Entity Central Index Key	0001110803
Current Fiscal Year End Date	--01-03
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Jul. 03, 2016
Document Fiscal Year Focus	2016
Document Fiscal Period Focus	Q2
Amendment Flag	false
Entity Common Stock, Shares Outstanding		146.6

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jul. 03, 2016	Jan. 03, 2016
Current assets:
Cash and cash equivalents	$ 951,662	$ 768,770
Short-term investments	473,594	617,450
Accounts receivable, net	372,480	385,529
Inventory	311,364	270,777
Prepaid expenses and other current assets	33,921	54,297
Total current assets	2,143,021	2,096,823
Property and equipment, net	511,354	342,694
Goodwill	775,995	752,629
Intangible assets, net	268,469	273,621
Deferred tax assets	186,462	134,515
Other assets	99,789	87,465
Total assets	3,985,090	3,687,747
Current liabilities:
Accounts payable	250,670	148,721
Accrued liabilities	330,326	386,844
Long-term debt, current portion	511	74,929
Total current liabilities	581,507	610,494
Long-term debt	1,031,370	1,015,649
Other long-term liabilities	198,568	180,505
Redeemable noncontrolling interests	33,733	32,546
Stockholders’ equity:
Common stock	1,878	1,859
Additional paid-in capital	2,664,865	2,497,501
Accumulated other comprehensive income	2,318	36
Retained earnings	1,232,764	1,022,765
Treasury stock, at cost	(1,846,054)	(1,673,608)
Total Illumina stockholders' equity	2,055,771	1,848,553
Noncontrolling interests	84,141
Total stockholders’ equity	2,139,912	1,848,553
Total liabilities and stockholders’ equity	$ 3,985,090	$ 3,687,747

Condensed Consolidated Statements of Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 03, 2016	Jun. 28, 2015	Jul. 03, 2016	Jun. 28, 2015
Revenue:
Product revenue	$ 509,922	$ 462,760	$ 992,672	$ 921,887
Service and other revenue	90,202	76,618	179,215	156,056
Total revenue	600,124	539,378	1,171,887	1,077,943
Cost of revenue:
Cost of product revenue	125,107	119,459	250,433	239,083
Cost of service and other revenue	40,663	32,170	79,550	64,699
Amortization of acquired intangible assets	10,549	11,384	21,045	22,769
Total cost of revenue	176,319	163,013	351,028	326,551
Gross profit	423,805	376,365	820,859	751,392
Operating expense:
Research and development	124,589	96,182	248,583	187,954
Selling, general and administrative	148,535	124,441	297,768	240,758
Legal contingencies	(11,490)		(9,490)
Headquarter relocation	302	1,480	684	2,179
Acquisition related expense (gain), net		2,329		(7,558)
Total operating expense	261,936	224,432	537,545	423,333
Income from operations	161,869	151,933	283,314	328,059
Other income (expense):
Interest income	3,403	1,344	4,627	3,037
Interest expense	(8,147)	(11,205)	(16,672)	(22,369)
Cost-method investment gain, net				12,582
Other (expense) income, net	(150)	(900)	1,302	(2,091)
Total other expense, net	(4,894)	(10,761)	(10,743)	(8,841)
Income before income taxes	156,975	141,172	272,571	319,218
Provision for income taxes	40,581	38,925	68,958	80,313
Consolidated net income	116,394	102,247	203,613	238,905
Add: Net loss attributable to noncontrolling interests	4,018		6,386
Net income attributable to Illumina stockholders	120,412	102,247	209,999	238,905
Net income attributable to Illumina stockholders for earnings per share	$ 121,971	$ 102,247	$ 211,558	$ 238,905
Earnings per share attributable to Illumina stockholders:
Basic (in dollars per share)	$ 0.83	$ 0.71	$ 1.44	$ 1.66
Diluted (in dollars per share)	$ 0.82	$ 0.69	$ 1.43	$ 1.61
Shares used in computing earnings per common share:
Basic (in shares)	146,778	144,220	146,822	143,996
Diluted (in shares)	147,889	148,969	148,123	148,826

Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 03, 2016	Jun. 28, 2015	Jul. 03, 2016	Jun. 28, 2015
Statement of Comprehensive Income [Abstract]
Consolidated net income	$ 116,394	$ 102,247	$ 203,613	$ 238,905
Unrealized gain (loss) on available-for-sale securities, net of deferred tax	336	(1,735)	2,282	1,679
Total consolidated comprehensive income	116,730	100,512	205,895	240,584
Add: Comprehensive loss attributable to noncontrolling interests	4,018		6,386
Comprehensive income attributable to Illumina stockholders	$ 120,748	$ 100,512	$ 212,281	$ 240,584

Condensed Consolidated Statement of Stockholders' Equity Statement - 6 months ended Jul. 03, 2016 - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Noncontrolling Interests [Member]
Beginning balance at Jan. 03, 2016	$ 1,848,553	$ 1,859	$ 2,497,501	$ 36	$ 1,022,765	$ (1,673,608)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	208,884				209,999		(1,115)
Unrealized gain on available-for-sale securities, net of deferred tax	2,282			2,282
Issuance of common stock, net of repurchases	(146,181)	19	26,592			(172,792)
Tax impact from the conversion of convertible notes	36		36
Share-based compensation	67,421		67,421
Net incremental tax benefit related to share-based compensation	83,690		83,690
Vesting of non-redeemable equity awards	0		(13)				(13)
Vesting of redeemable equity awards	(1,031)		(1,031)
Adjustment to the carrying value of redeemable noncontrolling interests	(5,426)		(5,426)
Issuance of subsidiary shares in business combination	2,298		2,102				196
Issuance of treasury stock	3,900		3,554			346
Contributions from noncontrolling interest owners	80,000						80,000
Proceeds from early exercise of equity awards from a subsidiary	5,047						5,047
Tax impact of deemed dividend from GRAIL	(9,561)		(9,561)
Ending balance at Jul. 03, 2016	$ 2,139,912	$ 1,878	$ 2,664,865	$ 2,318	$ 1,232,764	$ (1,846,054)	$ 84,141

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jul. 03, 2016	Jun. 28, 2015
Cash flows from operating activities:
Consolidated net income	$ 203,613	$ 238,905
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation expense	42,429	34,204
Amortization of intangible assets	25,143	26,598
Share-based compensation expense	67,262	64,875
Accretion of debt discount	15,009	20,376
Incremental tax benefit related to share-based compensation	(84,220)	(106,162)
Deferred income tax expense	27,829	80,581
Cost-method investment gain, net		(12,582)
Change in fair value of contingent consideration		(7,558)
Other	3,431	3,604
Changes in operating assets and liabilities:
Accounts receivable	13,490	(75,189)
Inventory	(40,586)	(32,526)
Prepaid expenses and other current assets	5,245	(1,382)
Other assets	(5,822)	(3,346)
Accounts payable	7,649	30,718
Accrued liabilities	(31,273)	(24,437)
Other long-term liabilities	7,586	1,545
Net cash provided by operating activities	256,785	238,224
Cash flows from investing activities:
Purchases of available-for-sale securities	(302,547)	(578,425)
Sales of available-for-sale securities	335,299	263,447
Maturities of available-for-sale securities	112,675	95,612
Net cash paid for acquisitions	(17,841)
Net (purchases of) sales proceeds from strategic investments	(6,371)	926
Purchases of property and equipment	(121,231)	(77,902)
Cash paid for intangible assets		275
Net cash used in investing activities	(16)	(296,617)
Cash flows from financing activities:
Payments on financing obligations	(71,572)	(8,664)
Payments on acquisition related contingent consideration liability	(29,200)
Proceeds from issuance of debt	2,042
Incremental tax benefit related to share-based compensation	84,220	106,162
Common stock repurchases	(100,000)	(34,753)
Taxes paid related to net share settlement of equity awards	(72,792)	(89,982)
Proceeds from issuance of common stock	26,561	42,513
Proceeds from early exercise of equity awards from a subsidiary	5,047
Contributions from noncontrolling interest owners	80,000
Net cash (used in) provided by financing activities	(75,694)	15,276
Effect of exchange rate changes on cash and cash equivalents	1,817	(1,980)
Net increase (decrease) in cash and cash equivalents	182,892	(45,097)
Cash and cash equivalents at beginning of period	768,770	636,154
Cash and cash equivalents at end of period	$ 951,662	$ 591,057

Basis of Presentation and Summary of Significant Accounting Policies

6 Months Ended

Jul. 03, 2016

Accounting Policies [Abstract]

Basis of Presentation and Summary of Significant Accounting Policies

Basis of Presentation

The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. Interim financial results are not necessarily indicative of results anticipated for the full year. These unaudited condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and footnotes included in the Company’s Annual Report on Form 10-K for the fiscal year ended January 3, 2016, from which the balance sheet information herein was derived. The preparation of financial statements requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenue, and expense, and related disclosure of contingent assets and liabilities. Actual results could differ from those estimates.

The unaudited condensed consolidated financial statements include the accounts of the Company, its wholly-owned subsidiaries, majority-owned or controlled companies, and variable interest entities (VIEs) for which the Company is the primary beneficiary. All intercompany transactions and balances have been eliminated in consolidation. In management’s opinion, the accompanying financial statements reflect all adjustments, consisting of normal recurring adjustments, considered necessary for a fair presentation of the results for the interim periods presented.

The Company evaluates its ownership, contractual and other interests in entities that are not wholly-owned by the Company to determine if these entities are VIEs, and, if so, whether the Company is the primary beneficiary of the VIE. In determining whether the Company is the primary beneficiary of a VIE and is therefore required to consolidate the VIE, the Company applies a qualitative approach that determines whether it has both (1) the power to direct the activities of the VIE that most significantly impact the VIE’s economic performance and (2) the obligation to absorb losses of, or the rights to receive benefits from, the VIE that could potentially be significant to that VIE. The Company continuously assesses whether it is the primary beneficiary of a VIE as changes to existing relationships or future transactions may result in the consolidation or deconsolidation, as the case may be. The Company has not provided financial or other support during the periods presented to its VIEs that it was not previously contractually required to provide.

The equity method is used to account for investments in which the Company has the ability to exercise significant influence, but not control, over the investee. Such investments are recorded within other assets, and the share of net income or losses of equity investments is recognized on a one quarter lag in other (income)/expense.

Segment Information

The Company is organized into three operating segments for purposes of recording and reporting its financial results. Two of the operating segments relate to the Company’s consolidated variable interest entities and are immaterial to the financial statements as a whole for all periods presented. Accordingly, the financial results for all operating segments have been reported on an aggregate basis as one reportable segment.

Fiscal Year

The Company’s fiscal year consists of 52 or 53 weeks ending the Sunday closest to December 31, with quarters of 13 or 14 weeks ending the Sunday closest to March 31, June 30, September 30, and December 31. The three and six months ended July 3, 2016 and June 28, 2015 were both 13 weeks.

Reclassifications

Certain prior period amounts have been reclassified to conform to the current period presentation.

Significant Accounting Policies

During the three and six months ended July 3, 2016, there have been no changes to the Company’s significant accounting policies as described in the Annual Report on Form 10-K for the fiscal year ended January 3, 2016.

Recent Accounting Pronouncements

In March 2016, the Financial Accounting Standards Board issued Accounting Standard Update (ASU) 2016-09, Compensation - Stock Compensation (Topic 718). The new standard requires income tax effects of stock compensation awards to be recognized in the income statement when the awards vest or are settled. The new standard also allows the Company to repurchase more of an employee’s shares for tax withholding purposes without triggering liability accounting and to make a policy election to account for forfeitures as they occur. ASU 2016-09 will be effective for the Company beginning in the first quarter of 2017. The Company is currently evaluating the impact of ASU 2016-09 on its consolidated financial statements.

In February 2016, the Financial Accounting Standards Board issued ASU 2016-02, Leases (Topic 842). The new standard requires lessees to recognize most leases on their balance sheets as lease liabilities with corresponding right-of-use assets and eliminates certain real estate-specific provisions. ASU 2016-02 will be effective for the Company beginning in the first quarter of 2019. ASU 2016-02 will be adopted on a modified retrospective transition basis for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. The Company is currently evaluating the impact of ASU 2016-02 on its consolidated financial statements.

In May 2014, the Financial Accounting Standards Board issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606). The new standard is based on the principle that revenue should be recognized to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ASU 2014-09 will be effective for the Company beginning in the first quarter of 2018 and allows for a full retrospective or a modified retrospective adoption approach. The Company is currently evaluating the impact of ASU 2014-09 on its consolidated financial statements.

Earnings per Share

Basic earnings per share attributable to Illumina stockholders is computed based on the weighted average number of common shares outstanding during the period. Diluted earnings per share attributable to Illumina stockholders is computed based on the sum of the weighted average number of common shares and potentially dilutive common shares outstanding during the period.

Potentially dilutive common shares consist of shares issuable under convertible senior notes, equity awards, and warrants. Convertible senior notes have a dilutive impact when the average market price of the Company’s common stock exceeds the applicable conversion price of the respective notes. Potentially dilutive common shares from equity awards and warrants are determined using the average share price for each period under the treasury stock method. In addition, the following amounts are assumed to be used to repurchase shares: proceeds from exercise of equity awards and warrants; the average amount of unrecognized compensation expense for equity awards; and estimated tax benefits that will be recorded in additional paid-in capital when expenses related to equity awards become deductible. In loss periods, basic net loss per share and diluted net loss per share are identical because the otherwise dilutive potential common shares become anti-dilutive and are therefore excluded.

The following table presents the calculation of weighted average shares used to calculate basic and diluted earnings per share (in thousands):



	Three Months Ended		Six Months Ended
	July 3, 2016	June 28, 2015	July 3, 2016	June 28, 2015
Weighted average shares outstanding	146,778	144,220	146,822	143,996
Effect of potentially dilutive common shares from:
Convertible senior notes	—	2,194	120	2,185
Equity awards	1,111	2,555	1,181	2,645
Weighted average shares used in calculating diluted earnings per share	147,889	148,969	148,123	148,826
Potentially dilutive shares excluded from calculation due to anti-dilutive effect	699	4	839	3

Balance Sheet Account Details

6 Months Ended

Jul. 03, 2016

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Balance Sheet Account Details

Short-Term Investments

The following is a summary of short-term investments (in thousands):



	July 3, 2016									January 3, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-sale securities:
Debt securities in government sponsored entities	$	18,141	$	—	$	(28	)	$	18,113	$	14,634	$	—	$	(8	)	$	14,626
Corporate debt securities	325,037		793		(76		)	325,754		422,177		44		(1,127		)	421,094
U.S. Treasury securities	129,265		462		—			129,727		182,144		3		(417		)	181,730
Total available-for-sale securities	$	472,443	$	1,255	$	(104	)	$	473,594	$	618,955	$	47	$	(1,552	)	$	617,450

Realized gains and losses are determined based on the specific identification method and are reported in interest income.

Contractual maturities of available-for-sale debt securities as of July 3, 2016 were as follows (in thousands):



	Estimated Fair Value
Due within one year	$	160,661
After one but within five years	312,933
Total	$	473,594

The Company has the ability, if necessary, to liquidate any of its cash equivalents and short-term investments in order to meet its liquidity needs in the next 12 months. Accordingly, those investments with contractual maturities greater than one year from the date of purchase nonetheless are classified as short-term on the accompanying condensed consolidated balance sheets.

Strategic Investments

As of July 3, 2016 and January 3, 2016, the aggregate carrying amounts of the Company’s cost-method investments in non-publicly traded companies included in other assets were $56.9 million and $56.6 million, respectively. Revenue recognized from transactions with such companies was $16.5 million and $29.6 million, respectively, for the three and six months ended July 3, 2016 and $14.1 million and $31.3 million, respectively, for the three and six months ended June 28, 2015.

During the six months ended June 28, 2015, the Company recognized a gain on a disposition of a cost-method investment of $15.1 million. The Company’s cost-method investments are assessed for impairment quarterly. The Company determines that it is not practicable to estimate the fair value of its cost-method investments on a regular basis and does not reassess the fair value of cost-method investments if there are no identified events or changes in circumstances that may have a significant adverse effect on the fair value of the investments. No material impairment loss was recorded during the three and six months ended July 3, 2016 or June 28, 2015.

On April 14, 2016, the Company announced that it has committed to invest $100.0 million in a new venture capital investment fund (the Fund). The capital commitment is callable over ten years, and up to $40.0 million can be drawn down during the first year. The Company’s investment in the Fund is accounted for as an equity method investment. During the six months ended July 3, 2016, the Company transferred $3.2 million of its cost-method investments to the Fund and contributed $3.1 million in cash.

Inventory

Inventory consists of the following (in thousands):



	July 3, 2016		January 3, 2016
Raw materials	$	102,413	$	97,740
Work in process	168,105		138,322
Finished goods	40,846		34,715
Total inventory	$	311,364	$	270,777

Property and Equipment

Property and equipment, net consists of the following (in thousands):



	July 3, 2016			January 3, 2016
Leasehold improvements	$	191,384		$	178,019
Machinery and equipment	250,412			224,158
Computer hardware and software	149,071			136,550
Furniture and fixtures	20,387			18,539
Building	7,670			7,670
Construction in progress	194,237			44,501
Total property and equipment, gross	813,161			609,437
Accumulated depreciation	(301,807		)	(266,743		)
Total property and equipment, net	$	511,354		$	342,694

Property and equipment, net included accrued expenditures of $106.2 million for the six months ended July 3, 2016, which includes $84.9 million in construction in progress recorded under build-to-suit lease accounting. Accrued capital expenditures were excluded from the condensed consolidated statements of cash flows. Accrued capital expenditures were immaterial for the six months ended June 28, 2015.

Goodwill

The Company tests the carrying value of goodwill in accordance with accounting rules on impairment of goodwill, which require the Company to estimate the fair value of the reporting unit annually, or when impairment indicators exist, and compare such amounts to their respective carrying values to determine if an impairment is required. The Company performed its annual assessment for goodwill impairment in the second quarter of 2016, noting no impairment.

Changes in the Company’s goodwill balance during the six months ended July 3, 2016 are as follows (in thousands):



	Goodwill
Balance as of January 3, 2016	$	752,629
Current period acquisitions	23,366
Balance as of July 3, 2016	$	775,995

In January 2016, the Company closed two acquisitions consisting of $17.8 million in upfront cash payments, equity

instruments, and certain contingent consideration provisions.

Derivatives

The Company is exposed to foreign exchange rate risks in the normal course of business. The Company enters into foreign exchange contracts to manage foreign currency risks related to monetary assets and liabilities that are denominated in currencies other than the U.S. dollar. These foreign exchange contracts are carried at fair value in other assets or other liabilities and are not designated as hedging instruments. Changes in the value of the derivative are recognized in other expense, net, along with the remeasurement gain or loss on the foreign currency denominated assets or liabilities.

As of July 3, 2016, the Company had foreign exchange forward contracts in place to hedge exposures in the euro, Japanese yen, and Australian dollar. As of July 3, 2016 and January 3, 2016, the total notional amounts of outstanding forward contracts in place for foreign currency purchases were $45.8 million and $61.3 million, respectively.

Accrued Liabilities

Accrued liabilities consist of the following (in thousands):



	July 3, 2016		January 3, 2016
Accrued compensation expenses	$	112,824	$	120,662
Deferred revenue, current portion	110,497		96,654
Accrued taxes payable	40,158		44,159
Customer deposits	8,388		20,901
Acquisition related contingent liability, current portion	6,529		35,000
Other	51,930		69,468
Total accrued liabilities	$	330,326	$	386,844

Warranties

The Company generally provides a one-year warranty on instruments. Additionally, the Company provides a warranty on consumables through the expiration date, which generally ranges from six to twelve months after the manufacture date. At the time revenue is recognized, the Company establishes an accrual for estimated warranty expenses based on historical experience as well as anticipated product performance. The Company periodically reviews its warranty reserve for adequacy and adjusts the warranty accrual, if necessary, based on actual experience and estimated costs to be incurred. Warranty expense is recorded as a component of cost of product revenue.

Changes in the Company’s reserve for product warranties during the three and six months ended July 3, 2016 and June 28, 2015 are as follows (in thousands):



	Three Months Ended						Six Months Ended
	July 3, 2016			June 28, 2015			July 3, 2016			June 28, 2015
Balance at beginning of period	$	15,820		$	15,991		$	16,717		$	15,616
Additions charged to cost of product revenue	6,672			6,924			13,323			13,821
Repairs and replacements	(6,813		)	(6,550		)	(14,361		)	(13,072		)
Balance at end of period	$	15,679		$	16,365		$	15,679		$	16,365

Leases

Changes in the Company’s facility exit obligation related to its former headquarters lease during the three and six months ended July 3, 2016 and June 28, 2015 are as follows (in thousands):



	Three Months Ended						Six Months Ended
	July 3, 2016			June 28, 2015			July 3, 2016			June 28, 2015
Balance at beginning of period	$	21,362		$	36,819		$	22,160		$	37,700
Adjustment to facility exit obligation	(26		)	657			21			657
Accretion of interest expense	328			729			663			1,336
Cash payments	(1,107		)	(1,528		)	(2,287		)	(3,016		)
Balance at end of period	$	20,557		$	36,677		$	20,557		$	36,677

During the six months ended July 3, 2016, the Company entered into an agreement to sublease its office building in San Francisco, California. The Company will receive $51.2 million in minimum lease payments during the initial term of approximately eight years.

On April 5, 2016, the Company entered into a lease agreement for certain office buildings being constructed in San Diego, California. Minimum lease payments during the initial term of ten years are estimated to be $127.4 million. The Company evaluated its involvement during the construction period, which includes certain indemnification obligations related to the construction. As a result, the Company is considered the owner of the construction project for accounting purposes only under build-to-suit lease accounting. As of July 3, 2016, the Company recorded $65.0 million in project construction costs incurred by the landlord as construction in progress and a corresponding amount in accounts payable, which were excluded from the consolidated statements of cash flow. Once the landlord completes the construction of each of the buildings, the Company will evaluate the lease in order to determine whether or not it meets the criteria for “sale-leaseback” treatment.

Investments in Consolidated Variable Interest Entities

GRAIL, Inc.

In January 2016, the Company obtained a majority equity ownership interest in GRAIL, Inc. (GRAIL), a company formed with unrelated third party investors to pursue the development and commercialization of a blood test for asymptomatic cancer screening. The Company determined that GRAIL is a variable interest entity as the entity lacks sufficient equity to finance its activities without additional support. Additionally, the Company determined that it has (a) control of the entity’s Board of Directors, which has unilateral power over the activities that most significantly impact the economic performance of GRAIL and (b) the obligation to absorb losses of and the right to receive benefits from GRAIL that are potentially significant to GRAIL. As a result, the Company is deemed to be the primary beneficiary of GRAIL and is required to consolidate GRAIL. On a fully diluted basis, the Company holds a 52% equity ownership interest in GRAIL as of July 3, 2016.

During the three months ended April 3, 2016, GRAIL completed its Series A convertible preferred stock financing, raising $120.0 million, of which the Company invested $40.0 million. Additionally, the Company and GRAIL executed a long-term supply agreement in which the Company contributed certain perpetual licenses, employees, and discounted supply terms in exchange for 112.5 million shares of GRAIL’s Class B Common Stock. Such contributions are recorded at their historical basis as they remain within the control of the Company. The $80.0 million received by GRAIL from unrelated third party investors upon issuance of its Series A convertible preferred stock is classified as noncontrolling interests in stockholders’ equity on the Company’s consolidated balance sheet.

During the three months ended July 3, 2016, GRAIL authorized for issuance 97.5 million shares of Series A-1 convertible preferred stock, all of which were issued to Illumina in exchange for 97.5 million shares of Illumina’s Class B Common Stock on June 23, 2016. As a result of the exchange, Illumina recorded a $9.5 million deemed dividend net of tax of $9.6 million through equity, which was eliminated in consolidation. Additionally, $1.6 million was added to net income attributable to Illumina stockholders for purposes of calculating Illumina’s consolidated earnings per share, which represents the deemed dividend, net of Illumina’s portion of the losses incurred by GRAIL’s common shareholders resulting from the exchange. For the three and six months ended July 3, 2016, the Company absorbed 90% of GRAIL’s losses based upon its proportional ownership of GRAIL’s common stock. Beginning July 4, 2016, the Company will absorb approximately 50% of GRAIL’s losses based upon its proportional ownership of GRAIL’s common stock subsequent to the exchange.

In accordance with GRAIL’s Equity Incentive Plan, the Company may be required to redeem certain vested stock awards in cash at the then approximate fair market value. The fair value of the redeemable noncontrolling interests is considered a Level 3 instrument. Such redemption right is exercisable at the option of the holder of the awards after February 28, 2021, provided that an initial public offering of GRAIL has not been completed. As the redemption provision is outside of the control of the Company, the redeemable noncontrolling interests in GRAIL are classified outside of stockholders’ equity on the accompanying condensed consolidated balance sheets. The balance of the redeemable noncontrolling interests is reported at the greater of its carrying value after receiving its allocation of GRAIL’s profits and losses or its estimated redemption value at each reporting date.

The assets and liabilities of GRAIL other than cash and cash equivalents are not significant to the Company’s financial position as of July 3, 2016 and have an immaterial impact on the Company’s condensed consolidated statements of income and cash flows for the three and six months ended July 3, 2016.

Helix Holdings I, LLC

In July 2015, the Company obtained a 50% voting equity ownership interest in Helix Holdings I, LLC (Helix), a limited liability company formed with unrelated third party investors to pursue the development and commercialization of a marketplace for consumer genomics. The Company determined that Helix is a variable interest entity as the holder of the at-risk equity investments as a group lack the power to direct the activities of Helix that most significantly impact Helix’s economic performance. Additionally, the Company determined that it has (a) unilateral power over one of the activities that most significantly impacts the economic performance of Helix through its contractual arrangements and no one individual party has unilateral power over the remaining significant activities of Helix and (b) the obligation to absorb losses of and the right to receive benefits from Helix that are potentially significant to Helix. As a result, the Company is deemed to be the primary beneficiary of Helix and is required to consolidate Helix.

As contractually committed, the Company contributed certain perpetual licenses, instruments, intangibles, initial laboratory setup, and discounted supply terms in exchange for voting equity interests in Helix. Such contributions are recorded at their historical basis as they remain within the control of the Company. Helix is financed through cash contributions made by the third party investors in exchange for voting equity interests in Helix.

Certain noncontrolling Helix investors may require the Company to redeem all noncontrolling interests in cash at the then approximate fair market value. The fair value of the redeemable noncontrolling interests is considered a Level 3 instrument. Such redemption right is exercisable at the option of certain noncontrolling interest holders after January 1, 2021, provided that a bona fide pursuit of the sale of Helix has occurred and an initial public offering of Helix has not been completed.

As the contingent redemption is outside of the control of Illumina, the redeemable noncontrolling interests in Helix are classified outside of stockholders’ equity on the consolidated balance sheet. The balance of the redeemable noncontrolling interests is reported at the greater of its carrying value after receiving its allocation of Helix’s profits and losses or its estimated redemption value at each reporting date. As of July 3, 2016, the noncontrolling shareholders and Illumina each held 50% of Helix’s outstanding voting equity interests.

The assets and liabilities of Helix are not significant to the Company’s financial position as of July 3, 2016. Helix has an immaterial impact on the Company’s condensed consolidated statements of income and cash flows for the three and six months ended July 3, 2016.

As of July 3, 2016, the accompanying condensed consolidated balance sheet includes $123.6 million of cash and cash equivalents attributable to GRAIL and Helix that will be used to settle their respective obligations and will not be available to settle obligations of the Company.

Redeemable Noncontrolling Interests

The activity of the redeemable noncontrolling interests during the six months ended July 3, 2016 is as follows (in thousands):



	Redeemable Noncontrolling Interests
Balance as of January 3, 2016	$	32,546
Vesting of redeemable equity awards	1,031
Net loss attributable to noncontrolling interests	(5,270		)
Adjustment up to the redemption value	5,426
Balance as of July 3, 2016	$	33,733

Fair Value Measurements

6 Months Ended

Jul. 03, 2016

Fair Value Disclosures [Abstract]

Fair Value Measurements

The following table presents the Company’s hierarchy for assets and liabilities measured at fair value on a recurring basis as of July 3, 2016 and January 3, 2016 (in thousands):



	July 3, 2016								January 3, 2016
	Level 1		Level 2		Level 3		Total		Level 1		Level 2		Level 3		Total
Assets:
Money market funds (cash equivalents)	$	682,706	$	—	$	—	$	682,706	$	391,246	$	—	$	—	$	391,246
Debt securities in government-sponsored entities	—		18,113		—		18,113		—		14,626		—		14,626
Corporate debt securities	—		325,754		—		325,754		—		421,094		—		421,094
U.S. Treasury securities	129,727		—		—		129,727		181,730		—		—		181,730
Deferred compensation plan assets	—		29,778		—		29,778		—		26,245		—		26,245
Total assets measured at fair value	$	812,433	$	373,645	$	—	$	1,186,078	$	572,976	$	461,965	$	—	$	1,034,941
Liabilities:
Acquisition related contingent consideration liabilities	$	—	$	—	$	5,300	$	5,300	$	—	$	—	$	35,000	$	35,000
Deferred compensation liability	—		27,791		—		27,791		—		24,925		—		24,925
Total liabilities measured at fair value	$	—	$	27,791	$	5,300	$	33,091	$	—	$	24,925	$	35,000	$	59,925

The Company holds available-for-sale securities that consist of highly liquid, investment grade debt securities. The Company considers information provided by the Company’s investment accounting and reporting service provider in the measurement of fair value of its debt securities. The investment service provider provides valuation information from an industry-recognized valuation service. Such valuations may be based on trade prices in active markets for identical assets or liabilities (Level 1 inputs) or valuation models using inputs that are observable either directly or indirectly (Level 2 inputs), such as quoted prices for similar assets or liabilities, yield curve, volatility factors, credit spreads, default rates, loss severity, current market and contractual prices for the underlying instruments or debt, broker and dealer quotes, as well as other relevant economic measures. The Company’s deferred compensation plan assets consist primarily of investments in life insurance contracts carried at cash surrender value, which reflects the net asset value of the underlying publicly traded mutual funds. The Company performs control procedures to corroborate the fair value of its holdings, including comparing valuations obtained from its investment service provider to valuations reported by the Company’s asset custodians, validation of pricing sources and models, and review of key model inputs if necessary.

As a result of an acquisition completed in January 2016, the Company recorded $5.3 million in contingent consideration liabilities, the majority of which are payable within 12 months after the acquisition date. The Company reassesses the fair value of any contingent consideration liabilities on a quarterly basis using the income approach. Assumptions used to estimate the acquisition date fair value of the contingent consideration include discount rates ranging from 4% to 6% and the probability of achieving certain milestones. This fair value measurement of the contingent consideration is based on significant inputs not observed in the market and thus represents a Level 3 measurement. Level 3 instruments are valued based on unobservable inputs that are supported by little or no market activity and reflect the Company’s own assumptions in measuring fair value.

Changes in estimated fair value of contingent consideration liabilities during the six months ended July 3, 2016 are as follows (in thousands):



	Contingent Consideration Liability (Level 3 Measurement)
Balance as of January 3, 2016	$	35,000
Additional liability recorded as a result of a current period acquisition	5,300
Cash payments	(35,000		)
Balance as of July 3, 2016	$	5,300

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Debt

6 Months Ended

Jul. 03, 2016

Debt Disclosure [Abstract]

Debt

Convertible Senior Notes

As of July 3, 2016, the Company had outstanding $632.5 million in principal amount of 0% convertible senior notes due June 15, 2019 (2019 Notes) and $517.5 million in principal amount of 0.5% convertible senior notes due June 15, 2021 (2021 Notes).

0% Convertible Senior Notes due 2019 and 0.5% Convertible Senior Notes due 2021

In June 2014, the Company issued $632.5 million aggregate principal amount of 2019 Notes and $517.5 million aggregate principal amount of 2021 Notes. The Company used the net proceeds plus cash on hand to repurchase a portion of the outstanding 2016 Notes in privately negotiated transactions concurrently with the issuance of the 2019 and 2021 Notes. The 2019 and 2021 Notes’ mature on June 15, 2019 and June 15, 2021, respectively, and the implied estimated effective rates of the liability components of the Notes were 2.9% and 3.5%, respectively, assuming no conversion.

Both the 2019 and 2021 Notes will be convertible into cash, shares of common stock, or a combination of cash and shares of common stock, at the Company's election, based on an initial conversion rate, subject to adjustment, of 3.9318 shares per $1,000 principal amount of the notes (which represents an initial conversion price of approximately $254.34 per share), only in the following circumstances and to the following extent: (1) during the five business-day period after any 10 consecutive trading day period (the measurement period) in which the trading price per 2019 and 2021 Note for each day of such measurement period was less than 98% of the product of the last reported sale price of the Company’s common stock and the conversion rate on each such day; (2) during any calendar quarter (and only during that quarter) after the calendar quarter ending September 30, 2014, if the last reported sale price of the Company’s common stock for 20 or more trading days in the period of 30 consecutive trading days ending on the last trading day of the immediately preceding calendar quarter exceeds 130% of the applicable conversion price in effect on the last trading day of the immediately preceding calendar quarter; (3) upon the occurrence of specified events described in the indenture for the 2019 and 2021 Notes; and (4) at any time on or after March 15, 2019 for the 2019 Notes, or March 15, 2021 for the 2021 Notes, through the second scheduled trading day immediately preceding the maturity date.

Neither the 2019 nor the 2021 Notes were convertible as of July 3, 2016 and had no dilutive impact during the three and six months ended July 3, 2016. If the 2019 and 2021 Notes were converted as of July 3, 2016, the if-converted value would not exceed the principal amount.

0.25% Convertible Senior Notes due 2016

In 2011, the Company issued $920.0 million aggregate principal amount of 0.25% convertible senior notes due 2016 (2016 Notes) with a maturity date of March 15, 2016. The effective rate of the liability component was estimated to be 4.5%. Based upon meeting the stock trading price conversion requirement during the three months ended March 30, 2014, the 2016 Notes became convertible on April 1, 2014 through, and including, March 11, 2016. All notes were converted by March 11, 2016.

During the six months ended July 3, 2016, the Company recorded a loss on extinguishment of debt calculated as the difference between the estimated fair value of the debt and the carrying value of the notes as of the settlement date. To measure the fair value of the converted notes as of the settlement date, the applicable interest rate was estimated using Level 2 observable inputs and applied to the converted notes using the same methodology as in the issuance date valuation. The loss recorded on extinguishment of debt for the six months ended July 3, 2016 was immaterial.

The following table summarizes information about the conversion of the 2016 Notes during the six months ended July 3, 2016 (in thousands):



	2016 Notes
Cash paid for principal of notes converted	$	75,543
Conversion value over principal amount paid in shares of common stock	$	63,753
Number of shares of common stock issued upon conversion	409

Summary of Convertible Senior Notes

The following table summarizes information about the equity and liability components of all convertible senior notes outstanding as of the period reported (dollars in thousands). The fair values of the respective notes outstanding were measured based on quoted market prices, and is a Level 2 measurement.



	July 3, 2016			January 3, 2016
Principal amount of convertible notes outstanding	$	1,150,000		$	1,225,547
Unamortized discount of liability component	(120,077		)	(134,969		)
Net carrying amount of liability component	1,029,923			1,090,578
Less: current portion	—			(74,929		)
Long-term debt	$	1,029,923		$	1,015,649
Carrying value of equity component, net of debt issuance cost	$	161,237		$	213,811
Fair value of outstanding notes	$	1,135,147		$	1,456,451
Weighted-average remaining amortization period of discount on the liability component	4.1 years			4.6 years

Other

As of July 3, 2016, the accompanying condensed consolidated balance sheets include $0.5 million and $1.5 million in current and long-term debt, respectively, related to an outstanding line of credit held by Helix.

Share-based Compensation Expense

6 Months Ended

Jul. 03, 2016

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Share-based Compensation Expense

Share-based compensation expense for all stock awards consists of the following (in thousands):



	Three Months Ended						Six Months Ended
	July 3, 2016			June 28, 2015			July 3, 2016			June 28, 2015
Cost of product revenue	$	1,958		$	2,113		$	4,150		$	4,445
Cost of service and other revenue	421			466			853			745
Research and development	10,693			10,747			21,374			22,054
Selling, general and administrative	18,898			19,631			40,885			37,631
Share-based compensation expense before taxes	31,970			32,957			67,262			64,875
Related income tax benefits	(7,667		)	(9,315		)	(15,478		)	(18,428		)
Share-based compensation expense, net of taxes	$	24,303		$	23,642		$	51,784		$	46,447

The assumptions used for the specified reporting periods and the resulting estimates of weighted-average fair value per share for stock purchased under the Employee Stock Purchase Plan (ESPP) during the six months ended July 3, 2016 are as follows:



	Employee Stock Purchase Rights
Risk-free interest rate	0.47		%
Expected volatility	40% - 44%
Expected term	0.5 - 1.0 year
Expected dividends	0		%
Weighted-average fair value per share	$	47.77

As of July 3, 2016, approximately $226.0 million of unrecognized compensation cost related to stock options, restricted stock, and ESPP shares granted to date is expected to be recognized over a weighted-average period of approximately 2.0 years.

Stockholders' Equity

6 Months Ended

Jul. 03, 2016

Equity [Abstract]

Stockholders' Equity

Stockholders’ Equity

As of July 3, 2016, approximately 7.6 million shares remained available for future grants under the 2015 Stock Plan and the 2005 Solexa Equity Plan.

Restricted Stock

The Company’s restricted stock activity and related information for the six months ended July 3, 2016 is as follows (units in thousands):



	Restricted Stock Awards (RSA)	Restricted Stock Units (RSU)		Performance Stock Units (PSU)(1)		Weighted-Average Grant-Date Fair Value per Share
	Restricted Stock Awards (RSA)	Restricted Stock Units (RSU)		Performance Stock Units (PSU)(1)		RSA		RSU		PSU
Outstanding at January 3, 2016	21	2,206		583		$	47.93	$	131.80	$	169.41
Awarded	22	121		12		$	179.00	$	154.96	$	164.66
Vested	—	(321	)	—		$	—	$	82.91	—
Cancelled	—	(153	)	(97	)	$	—	$	135.36	$	163.06
Outstanding at July 3, 2016	43	1,853		498		$	114.59	$	141.46	$	170.54

______________________________________


(1)	The number of units reflect the estimated number of shares to be issued at the end of the performance period.

Stock Options

The Company’s stock option activity under all stock option plans during the six months ended July 3, 2016 is as follows:



	Options (in thousands)		Weighted-Average Exercise Price
Outstanding at January 3, 2016	1,599		$	41.95
Exercised	(331	)	$	30.14
Cancelled	(2	)	$	48.36
Outstanding at July 3, 2016	1,266		$	45.04

At July 3, 2016, outstanding options to purchase 1.3 million shares were exercisable with a weighted-average exercise price per share of $45.09.

Employee Stock Purchase Plan

The price at which common stock is purchased under the ESPP is equal to 85% of the fair market value of the common stock on the first day of the offering period or purchase date, whichever is lower. During the six months ended July 3, 2016, approximately 0.1 million shares were issued under the ESPP. As of July 3, 2016, there were approximately 14.4 million shares available for issuance under the ESPP.

Share Repurchases

On May 1, 2015, the Company’s Board of Directors authorized $150.0 million of repurchases under a Rule 10b5-1 plan. In addition, on October 29, 2015, the Company’s Board of Directors authorized a new discretionary share repurchase program of $250.0 million. During the six months ended July 3, 2016, the Company repurchased approximately 0.7 million shares for $100.0 million in aggregate. Authorizations to repurchase up to an additional $156.1 million of the Company’s common stock remained available as of July 3, 2016.

Income Taxes	6 Months Ended
Income Taxes	Jul. 03, 2016
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company’s effective tax rate may vary from the U.S. federal statutory tax rate due to the change in the mix of earnings in tax jurisdictions with different statutory rates, benefits related to tax credits, and the tax impact of non-deductible expenses and other permanent differences between income before income taxes and taxable income. The effective tax rates for the three and six months ended July 3, 2016 was 25.9% and 25.3%, respectively. For the three and six months ended July 3, 2016, the variance from the U.S. federal statutory tax rate of 35% was primarily attributable to the mix of earnings in jurisdictions with lower statutory tax rates than the U.S. federal statutory tax rate, such as in Singapore and the United Kingdom.

Legal Proceedings	6 Months Ended
Legal Proceedings	Jul. 03, 2016
Commitments and Contingencies Disclosure [Abstract]
Legal Proceedings	Legal Proceedings The Company is involved in various lawsuits and claims arising in the ordinary course of business, including actions with respect to intellectual property, employment, and contractual matters. In connection with these matters, the Company assesses, on a regular basis, the probability and range of possible loss based on the developments in these matters. A liability is recorded in the financial statements if it is believed to be probable that a loss has been incurred and the amount of the loss can be reasonably estimated. Because litigation is inherently unpredictable and unfavorable results could occur, assessing contingencies is highly subjective and requires judgments about future events. The Company regularly reviews outstanding legal matters to determine the adequacy of the liabilities accrued and related disclosures. The amount of ultimate loss may differ from these estimates. Each matter presents its own unique circumstances, and prior litigation does not necessarily provide a reliable basis on which to predict the outcome, or range of outcomes, in any individual proceeding. Because of the uncertainties related to the occurrence, amount, and range of loss on any pending litigation or claim, the Company is currently unable to predict their ultimate outcome, and, with respect to any pending litigation or claim where no liability has been accrued, to make a meaningful estimate of the reasonably possible loss or range of loss that could result from an unfavorable outcome. In the event that opposing litigants or claims ultimately succeed at trial and any subsequent appeals on their claims, any potential loss or charges in excess of any established accruals, individually or in the aggregate, could have a material adverse effect on the Company’s business, financial condition, results of operations, and/or cash flows in the period in which the unfavorable outcome occurs or becomes probable, and potentially in future periods. On July 1, 2016, the Company entered into a Settlement and License Agreement with Enzo Life Sciences, Inc. (Enzo) that settled all claims in the litigation. Pursuant to the terms of the Settlement and License Agreement, the Company paid Enzo a one-time payment of $21.0 million for release of past damages claimed and a fully paid-up non-exclusive license to U.S. Patent No. 7,064,197. None of the parties made any admission of liability in entering into the Settlement and License Agreement. The Company allocated the $21.0 million settlement on a relative fair value basis, resulting in $11.5 million capitalized as an intangible asset and a corresponding gain recorded in legal contingencies for the value of the license, which will be amortized over a period of 7 years on a straight-line basis, and the remaining $9.5 million related to past damages claimed. The fair value of the license and past damages was estimated using a discounted cash flow model, and is considered to be a Level 3 measurement. The $21.0 million settlement liability is included in accounts payable as of July 3, 2016.

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jul. 03, 2016
Accounting Policies [Abstract]
Basis of Presentation	The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements.
Consolidation	The unaudited condensed consolidated financial statements include the accounts of the Company, its wholly-owned subsidiaries, majority-owned or controlled companies, and variable interest entities (VIEs) for which the Company is the primary beneficiary. All intercompany transactions and balances have been eliminated in consolidation. In management’s opinion, the accompanying financial statements reflect all adjustments, consisting of normal recurring adjustments, considered necessary for a fair presentation of the results for the interim periods presented.
Variable Interest Entity	The Company evaluates its ownership, contractual and other interests in entities that are not wholly-owned by the Company to determine if these entities are VIEs, and, if so, whether the Company is the primary beneficiary of the VIE. In determining whether the Company is the primary beneficiary of a VIE and is therefore required to consolidate the VIE, the Company applies a qualitative approach that determines whether it has both (1) the power to direct the activities of the VIE that most significantly impact the VIE’s economic performance and (2) the obligation to absorb losses of, or the rights to receive benefits from, the VIE that could potentially be significant to that VIE. The Company continuously assesses whether it is the primary beneficiary of a VIE as changes to existing relationships or future transactions may result in the consolidation or deconsolidation, as the case may be.
Segment Information	The Company is organized into three operating segments for purposes of recording and reporting its financial results. Two of the operating segments relate to the Company’s consolidated variable interest entities and are immaterial to the financial statements as a whole for all periods presented. Accordingly, the financial results for all operating segments have been reported on an aggregate basis as one reportable segment.
Fiscal Year	The Company’s fiscal year consists of 52 or 53 weeks ending the Sunday closest to December 31, with quarters of 13 or 14 weeks ending the Sunday closest to March 31, June 30, September 30, and December 31. The three and six months ended July 3, 2016 and June 28, 2015 were both 13 weeks.
Reclassifications	Certain prior period amounts have been reclassified to conform to the current period presentation.
Recent Accounting Pronouncements	In March 2016, the Financial Accounting Standards Board issued Accounting Standard Update (ASU) 2016-09, Compensation - Stock Compensation (Topic 718). The new standard requires income tax effects of stock compensation awards to be recognized in the income statement when the awards vest or are settled. The new standard also allows the Company to repurchase more of an employee’s shares for tax withholding purposes without triggering liability accounting and to make a policy election to account for forfeitures as they occur. ASU 2016-09 will be effective for the Company beginning in the first quarter of 2017. The Company is currently evaluating the impact of ASU 2016-09 on its consolidated financial statements. In February 2016, the Financial Accounting Standards Board issued ASU 2016-02, Leases (Topic 842). The new standard requires lessees to recognize most leases on their balance sheets as lease liabilities with corresponding right-of-use assets and eliminates certain real estate-specific provisions. ASU 2016-02 will be effective for the Company beginning in the first quarter of 2019. ASU 2016-02 will be adopted on a modified retrospective transition basis for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. The Company is currently evaluating the impact of ASU 2016-02 on its consolidated financial statements. In May 2014, the Financial Accounting Standards Board issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606). The new standard is based on the principle that revenue should be recognized to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ASU 2014-09 will be effective for the Company beginning in the first quarter of 2018 and allows for a full retrospective or a modified retrospective adoption approach. The Company is currently evaluating the impact of ASU 2014-09 on its consolidated financial statements.
Earnings per Share	Basic earnings per share attributable to Illumina stockholders is computed based on the weighted average number of common shares outstanding during the period. Diluted earnings per share attributable to Illumina stockholders is computed based on the sum of the weighted average number of common shares and potentially dilutive common shares outstanding during the period. Potentially dilutive common shares consist of shares issuable under convertible senior notes, equity awards, and warrants. Convertible senior notes have a dilutive impact when the average market price of the Company’s common stock exceeds the applicable conversion price of the respective notes. Potentially dilutive common shares from equity awards and warrants are determined using the average share price for each period under the treasury stock method. In addition, the following amounts are assumed to be used to repurchase shares: proceeds from exercise of equity awards and warrants; the average amount of unrecognized compensation expense for equity awards; and estimated tax benefits that will be recorded in additional paid-in capital when expenses related to equity awards become deductible. In loss periods, basic net loss per share and diluted net loss per share are identical because the otherwise dilutive potential common shares become anti-dilutive and are therefore excluded.
Derivatives	The Company is exposed to foreign exchange rate risks in the normal course of business. The Company enters into foreign exchange contracts to manage foreign currency risks related to monetary assets and liabilities that are denominated in currencies other than the U.S. dollar. These foreign exchange contracts are carried at fair value in other assets or other liabilities and are not designated as hedging instruments. Changes in the value of the derivative are recognized in other expense, net, along with the remeasurement gain or loss on the foreign currency denominated assets or liabilities.
Warranties	The Company generally provides a one-year warranty on instruments. Additionally, the Company provides a warranty on consumables through the expiration date, which generally ranges from six to twelve months after the manufacture date. At the time revenue is recognized, the Company establishes an accrual for estimated warranty expenses based on historical experience as well as anticipated product performance. The Company periodically reviews its warranty reserve for adequacy and adjusts the warranty accrual, if necessary, based on actual experience and estimated costs to be incurred. Warranty expense is recorded as a component of cost of product revenue.

Basis of Presentation and Summary of Significant Accounting Policies (Tables)

6 Months Ended

Jul. 03, 2016

Accounting Policies [Abstract]

Summary of Calculation of Weighted Average Shares used to Calculate Basic and Diluted Earnings Per Share, Earnings Per Share

The following table presents the calculation of weighted average shares used to calculate basic and diluted earnings per share (in thousands):



	Three Months Ended		Six Months Ended
	July 3, 2016	June 28, 2015	July 3, 2016	June 28, 2015
Weighted average shares outstanding	146,778	144,220	146,822	143,996
Effect of potentially dilutive common shares from:
Convertible senior notes	—	2,194	120	2,185
Equity awards	1,111	2,555	1,181	2,645
Weighted average shares used in calculating diluted earnings per share	147,889	148,969	148,123	148,826
Potentially dilutive shares excluded from calculation due to anti-dilutive effect	699	4	839	3

Summary of Calculation of Weighted Average Shares used to Calculate Basic and Diluted Earnings Per Share, Antidilutive Securities

The following table presents the calculation of weighted average shares used to calculate basic and diluted earnings per share (in thousands):



	Three Months Ended		Six Months Ended
	July 3, 2016	June 28, 2015	July 3, 2016	June 28, 2015
Weighted average shares outstanding	146,778	144,220	146,822	143,996
Effect of potentially dilutive common shares from:
Convertible senior notes	—	2,194	120	2,185
Equity awards	1,111	2,555	1,181	2,645
Weighted average shares used in calculating diluted earnings per share	147,889	148,969	148,123	148,826
Potentially dilutive shares excluded from calculation due to anti-dilutive effect	699	4	839	3

Balance Sheet Account Details (Tables)

6 Months Ended

Jul. 03, 2016

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Summary of Short-term Investments

The following is a summary of short-term investments (in thousands):



	July 3, 2016									January 3, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-sale securities:
Debt securities in government sponsored entities	$	18,141	$	—	$	(28	)	$	18,113	$	14,634	$	—	$	(8	)	$	14,626
Corporate debt securities	325,037		793		(76		)	325,754		422,177		44		(1,127		)	421,094
U.S. Treasury securities	129,265		462		—			129,727		182,144		3		(417		)	181,730
Total available-for-sale securities	$	472,443	$	1,255	$	(104	)	$	473,594	$	618,955	$	47	$	(1,552	)	$	617,450

Summary of Contractual Maturities of Available-for-sale Debt Securities

Contractual maturities of available-for-sale debt securities as of July 3, 2016 were as follows (in thousands):



	Estimated Fair Value
Due within one year	$	160,661
After one but within five years	312,933
Total	$	473,594

Summary of Inventory

Inventory consists of the following (in thousands):



	July 3, 2016		January 3, 2016
Raw materials	$	102,413	$	97,740
Work in process	168,105		138,322
Finished goods	40,846		34,715
Total inventory	$	311,364	$	270,777

Summary of Property and Equipment

Property and equipment, net consists of the following (in thousands):



	July 3, 2016			January 3, 2016
Leasehold improvements	$	191,384		$	178,019
Machinery and equipment	250,412			224,158
Computer hardware and software	149,071			136,550
Furniture and fixtures	20,387			18,539
Building	7,670			7,670
Construction in progress	194,237			44,501
Total property and equipment, gross	813,161			609,437
Accumulated depreciation	(301,807		)	(266,743		)
Total property and equipment, net	$	511,354		$	342,694

Summary of Changes in Goodwill

Changes in the Company’s goodwill balance during the six months ended July 3, 2016 are as follows (in thousands):



	Goodwill
Balance as of January 3, 2016	$	752,629
Current period acquisitions	23,366
Balance as of July 3, 2016	$	775,995

Summary of Accrued Liabilities

Accrued liabilities consist of the following (in thousands):



	July 3, 2016		January 3, 2016
Accrued compensation expenses	$	112,824	$	120,662
Deferred revenue, current portion	110,497		96,654
Accrued taxes payable	40,158		44,159
Customer deposits	8,388		20,901
Acquisition related contingent liability, current portion	6,529		35,000
Other	51,930		69,468
Total accrued liabilities	$	330,326	$	386,844

Summary of Changes in Reserve for Product Warranties

Changes in the Company’s reserve for product warranties during the three and six months ended July 3, 2016 and June 28, 2015 are as follows (in thousands):



	Three Months Ended						Six Months Ended
	July 3, 2016			June 28, 2015			July 3, 2016			June 28, 2015
Balance at beginning of period	$	15,820		$	15,991		$	16,717		$	15,616
Additions charged to cost of product revenue	6,672			6,924			13,323			13,821
Repairs and replacements	(6,813		)	(6,550		)	(14,361		)	(13,072		)
Balance at end of period	$	15,679		$	16,365		$	15,679		$	16,365

Summary of Changes in Facility Exit Obligation Related to the Former Headquarters Lease

Changes in the Company’s facility exit obligation related to its former headquarters lease during the three and six months ended July 3, 2016 and June 28, 2015 are as follows (in thousands):



	Three Months Ended						Six Months Ended
	July 3, 2016			June 28, 2015			July 3, 2016			June 28, 2015
Balance at beginning of period	$	21,362		$	36,819		$	22,160		$	37,700
Adjustment to facility exit obligation	(26		)	657			21			657
Accretion of interest expense	328			729			663			1,336
Cash payments	(1,107		)	(1,528		)	(2,287		)	(3,016		)
Balance at end of period	$	20,557		$	36,677		$	20,557		$	36,677

Summary of Activity of Redeemable Noncontrolling Interests

The activity of the redeemable noncontrolling interests during the six months ended July 3, 2016 is as follows (in thousands):



	Redeemable Noncontrolling Interests
Balance as of January 3, 2016	$	32,546
Vesting of redeemable equity awards	1,031
Net loss attributable to noncontrolling interests	(5,270		)
Adjustment up to the redemption value	5,426
Balance as of July 3, 2016	$	33,733

Fair Value Measurements (Tables)

6 Months Ended

Jul. 03, 2016

Fair Value Disclosures [Abstract]

Summary of Hierarchy for Assets and Liabilities Measured at Fair Value on a Recurring Basis

The following table presents the Company’s hierarchy for assets and liabilities measured at fair value on a recurring basis as of July 3, 2016 and January 3, 2016 (in thousands):



	July 3, 2016								January 3, 2016
	Level 1		Level 2		Level 3		Total		Level 1		Level 2		Level 3		Total
Assets:
Money market funds (cash equivalents)	$	682,706	$	—	$	—	$	682,706	$	391,246	$	—	$	—	$	391,246
Debt securities in government-sponsored entities	—		18,113		—		18,113		—		14,626		—		14,626
Corporate debt securities	—		325,754		—		325,754		—		421,094		—		421,094
U.S. Treasury securities	129,727		—		—		129,727		181,730		—		—		181,730
Deferred compensation plan assets	—		29,778		—		29,778		—		26,245		—		26,245
Total assets measured at fair value	$	812,433	$	373,645	$	—	$	1,186,078	$	572,976	$	461,965	$	—	$	1,034,941
Liabilities:
Acquisition related contingent consideration liabilities	$	—	$	—	$	5,300	$	5,300	$	—	$	—	$	35,000	$	35,000
Deferred compensation liability	—		27,791		—		27,791		—		24,925		—		24,925
Total liabilities measured at fair value	$	—	$	27,791	$	5,300	$	33,091	$	—	$	24,925	$	35,000	$	59,925

Summary of Changes in Estimated Fair Value of Contingent Consideration Liabilities

Changes in estimated fair value of contingent consideration liabilities during the six months ended July 3, 2016 are as follows (in thousands):



	Contingent Consideration Liability (Level 3 Measurement)
Balance as of January 3, 2016	$	35,000
Additional liability recorded as a result of a current period acquisition	5,300
Cash payments	(35,000		)
Balance as of July 3, 2016	$	5,300

Debt (Tables)

6 Months Ended

Jul. 03, 2016

Debt Disclosure [Abstract]

Summary of Conversion of 2016 Notes

The following table summarizes information about the conversion of the 2016 Notes during the six months ended July 3, 2016 (in thousands):



	2016 Notes
Cash paid for principal of notes converted	$	75,543
Conversion value over principal amount paid in shares of common stock	$	63,753
Number of shares of common stock issued upon conversion	409

Summary of Information about Equity and Liability Components of Convertible Senior Notes Outstanding

The following table summarizes information about the equity and liability components of all convertible senior notes outstanding as of the period reported (dollars in thousands). The fair values of the respective notes outstanding were measured based on quoted market prices, and is a Level 2 measurement.



	July 3, 2016			January 3, 2016
Principal amount of convertible notes outstanding	$	1,150,000		$	1,225,547
Unamortized discount of liability component	(120,077		)	(134,969		)
Net carrying amount of liability component	1,029,923			1,090,578
Less: current portion	—			(74,929		)
Long-term debt	$	1,029,923		$	1,015,649
Carrying value of equity component, net of debt issuance cost	$	161,237		$	213,811
Fair value of outstanding notes	$	1,135,147		$	1,456,451
Weighted-average remaining amortization period of discount on the liability component	4.1 years			4.6 years

Share-based Compensation Expense (Tables)

6 Months Ended

Jul. 03, 2016

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of Share-based Compensation Expense for all Stock Awards

Share-based compensation expense for all stock awards consists of the following (in thousands):



	Three Months Ended						Six Months Ended
	July 3, 2016			June 28, 2015			July 3, 2016			June 28, 2015
Cost of product revenue	$	1,958		$	2,113		$	4,150		$	4,445
Cost of service and other revenue	421			466			853			745
Research and development	10,693			10,747			21,374			22,054
Selling, general and administrative	18,898			19,631			40,885			37,631
Share-based compensation expense before taxes	31,970			32,957			67,262			64,875
Related income tax benefits	(7,667		)	(9,315		)	(15,478		)	(18,428		)
Share-based compensation expense, net of taxes	$	24,303		$	23,642		$	51,784		$	46,447

Summary of Assumptions used to Estimate the Weighted-Average Fair Value Per Share for Stock Purchase under the Employee Stock Purchase Plan

The assumptions used for the specified reporting periods and the resulting estimates of weighted-average fair value per share for stock purchased under the Employee Stock Purchase Plan (ESPP) during the six months ended July 3, 2016 are as follows:



	Employee Stock Purchase Rights
Risk-free interest rate	0.47		%
Expected volatility	40% - 44%
Expected term	0.5 - 1.0 year
Expected dividends	0		%
Weighted-average fair value per share	$	47.77

Stockholders' Equity (Tables)

6 Months Ended

Jul. 03, 2016

Equity [Abstract]

Summary of Restricted Stock Activity and Related Information, Restricted Stock

The Company’s restricted stock activity and related information for the six months ended July 3, 2016 is as follows (units in thousands):



	Restricted Stock Awards (RSA)	Restricted Stock Units (RSU)		Performance Stock Units (PSU)(1)		Weighted-Average Grant-Date Fair Value per Share
	Restricted Stock Awards (RSA)	Restricted Stock Units (RSU)		Performance Stock Units (PSU)(1)		RSA		RSU		PSU
Outstanding at January 3, 2016	21	2,206		583		$	47.93	$	131.80	$	169.41
Awarded	22	121		12		$	179.00	$	154.96	$	164.66
Vested	—	(321	)	—		$	—	$	82.91	—
Cancelled	—	(153	)	(97	)	$	—	$	135.36	$	163.06
Outstanding at July 3, 2016	43	1,853		498		$	114.59	$	141.46	$	170.54

______________________________________


(1)	The number of units reflect the estimated number of shares to be issued at the end of the performance period.

Summary of Restricted Stock Activity and Related Information, Performance Units

The Company’s restricted stock activity and related information for the six months ended July 3, 2016 is as follows (units in thousands):



	Restricted Stock Awards (RSA)	Restricted Stock Units (RSU)		Performance Stock Units (PSU)(1)		Weighted-Average Grant-Date Fair Value per Share
	Restricted Stock Awards (RSA)	Restricted Stock Units (RSU)		Performance Stock Units (PSU)(1)		RSA		RSU		PSU
Outstanding at January 3, 2016	21	2,206		583		$	47.93	$	131.80	$	169.41
Awarded	22	121		12		$	179.00	$	154.96	$	164.66
Vested	—	(321	)	—		$	—	$	82.91	—
Cancelled	—	(153	)	(97	)	$	—	$	135.36	$	163.06
Outstanding at July 3, 2016	43	1,853		498		$	114.59	$	141.46	$	170.54

______________________________________


(1)	The number of units reflect the estimated number of shares to be issued at the end of the performance period.

Summary of Stock Option Activity Under all Stock Option Plans

The Company’s stock option activity under all stock option plans during the six months ended July 3, 2016 is as follows:



	Options (in thousands)		Weighted-Average Exercise Price
Outstanding at January 3, 2016	1,599		$	41.95
Exercised	(331	)	$	30.14
Cancelled	(2	)	$	48.36
Outstanding at July 3, 2016	1,266		$	45.04

Basis of Presentation and Summary of Significant Accounting Policies - Summary of Calculation of Weighted Average Shares used to Calculate Basic and Diluted Earnings Per Share (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jul. 03, 2016	Jun. 28, 2015	Jul. 03, 2016	Jun. 28, 2015
Weighted average shares used to calculate basic and diluted earnings per share
Weighted average shares outstanding	146,778	144,220	146,822	143,996
Effect of potentially dilutive common shares from:
Convertible senior notes		2,194	120	2,185
Equity awards	1,111	2,555	1,181	2,645
Weighted average shares used in calculating diluted earnings per share	147,889	148,969	148,123	148,826
Potentially dilutive shares excluded from calculation due to anti-dilutive effect	699	4	839	3

Balance Sheet Account Details - Summary of Short-term Investments (Details) - USD ($) $ in Thousands	Jul. 03, 2016	Jan. 03, 2016
Available-for-sale securities:
Amortized Cost	$ 472,443	$ 618,955
Gross Unrealized Gains	1,255	47
Gross Unrealized Losses	(104)	(1,552)
Estimated Fair Value	473,594	617,450
Debt securities in government sponsored entities [Member]
Available-for-sale securities:
Amortized Cost	18,141	14,634
Gross Unrealized Losses	(28)	(8)
Estimated Fair Value	18,113	14,626
Corporate debt securities [Member]
Available-for-sale securities:
Amortized Cost	325,037	422,177
Gross Unrealized Gains	793	44
Gross Unrealized Losses	(76)	(1,127)
Estimated Fair Value	325,754	421,094
U.S. Treasury securities [Member]
Available-for-sale securities:
Amortized Cost	129,265	182,144
Gross Unrealized Gains	462	3
Gross Unrealized Losses		(417)
Estimated Fair Value	$ 129,727	$ 181,730

Balance Sheet Account Details - Summary of Contractual Maturities of Available-for-sale Debt Securities (Details) $ in Thousands	Jul. 03, 2016 USD ($)
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Due within one year	$ 160,661
After one but within five years	312,933
Total	$ 473,594

Balance Sheet Account Details - Narrative - Strategic Investments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 03, 2016	Jun. 28, 2015	Jul. 03, 2016	Jun. 28, 2015	Apr. 14, 2016	Jan. 03, 2016
Schedule of Investments [Line Items]
Cost-method investment gain				$ 15.1
Other commitment					$ 100.0
Callable period			10 years
Capital commitment draw down allowed			$ 40.0
Cost-Method Investee [Member]
Schedule of Investments [Line Items]
Revenue from transactions with Company's cost-method investments in non-publicly traded companies	$ 16.5	$ 14.1	29.6	$ 31.3
Other Assets [Member]
Schedule of Investments [Line Items]
Company's cost-method investments in non-publicly traded companies	56.9		56.9			$ 56.6
Equity method investments	3.2		3.2
Cash and Cash Equivalents [Member]
Schedule of Investments [Line Items]
Equity method investments	$ 3.1		$ 3.1

Balance Sheet Account Details - Summary of Inventory (Details) - USD ($) $ in Thousands	Jul. 03, 2016	Jan. 03, 2016
Inventory [Abstract]
Raw materials	$ 102,413	$ 97,740
Work in process	168,105	138,322
Finished goods	40,846	34,715
Total inventory	$ 311,364	$ 270,777

Balance Sheet Account Details - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	Jul. 03, 2016	Jan. 03, 2016
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 813,161	$ 609,437
Accumulated depreciation	301,807	266,743
Total property and equipment, net	511,354	342,694
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	191,384	178,019
Machinery and equipment
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	250,412	224,158
Computer hardware and software
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	149,071	136,550
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	20,387	18,539
Building
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	7,670	7,670
Construction in progress
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 194,237	$ 44,501

Balance Sheet Account Details - Narrative - Property and Equipment (Details) $ in Millions	6 Months Ended
	Jul. 03, 2016 USD ($)
Property, Plant and Equipment [Line Items]
Accrued expenditures included in capital expenditures	$ 106.2
Construction in progress
Property, Plant and Equipment [Line Items]
Accrued expenditures included in capital expenditures	$ 84.9

Balance Sheet Account Details - Summary of Changes in Goodwill (Details) $ in Thousands	6 Months Ended
	Jul. 03, 2016 USD ($)
Goodwill [Roll Forward]
Beginning balance	$ 752,629
Current period acquisitions	23,366
Ending balance	$ 775,995

Balance Sheet Account Details - Narrative - Goodwill (Details) $ in Millions	1 Months Ended
	Jan. 31, 2016 USD ($) business
Goodwill and Intangible Assets Disclosure [Abstract]
Number of acquisitions closed \| business	2
Upfront cash payments, equity instruments and certain contingent consideration provisions \| $	$ 17.8

Balance Sheet Account Details - Narrative - Derivatives (Details) - USD ($) $ in Millions	Jul. 03, 2016	Jan. 03, 2016
Not Designated as Hedging Instrument [Member] \| Foreign Exchange Forward [Member]
Derivative [Line Items]
Derivative, notional amount	$ 45.8	$ 61.3

Balance Sheet Account Details - Summary of Accrued Liabilities (Details) - USD ($) $ in Thousands	Jul. 03, 2016	Jan. 03, 2016
Accrued Liabilities, Current [Abstract]
Accrued compensation expenses	$ 112,824	$ 120,662
Deferred revenue, current portion	110,497	96,654
Accrued taxes payable	40,158	44,159
Customer deposits	8,388	20,901
Acquisition related contingent liability, current portion	6,529	35,000
Other	51,930	69,468
Total accrued liabilities	$ 330,326	$ 386,844

Balance Sheet Account Details - Narrative - Warranties (Details)	6 Months Ended
	Jul. 03, 2016
Instruments [Member]
Product Warranty Liability [Line Items]
Warranty period	1 year
Consumables [Member] \| Minimum [Member]
Product Warranty Liability [Line Items]
Warranty period	6 months
Consumables [Member] \| Maximum [Member]
Product Warranty Liability [Line Items]
Warranty period	12 months

Balance Sheet Account Details - Summary of Changes in Reserve for Product Warranties (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 03, 2016	Jun. 28, 2015	Jul. 03, 2016	Jun. 28, 2015
Reserve for product warranties [Roll Forward]
Balance at beginning of period	$ 15,820	$ 15,991	$ 16,717	$ 15,616
Additions charged to cost of product revenue	6,672	6,924	13,323	13,821
Repairs and replacements	(6,813)	(6,550)	(14,361)	(13,072)
Balance at end of period	$ 15,679	$ 16,365	$ 15,679	$ 16,365

Balance Sheet Account Details - Summary of Changes in Facility Exit Obligation Related to the Former Headquarters Lease (Details) - Facility Exit Obligation [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 03, 2016	Jun. 28, 2015	Jul. 03, 2016	Jun. 28, 2015
Headquarter Facility Exit Obligation [Roll Forward]
Balance at beginning of period	$ 21,362	$ 36,819	$ 22,160	$ 37,700
Adjustment to facility exit obligation	(26)	657	21	657
Accretion of interest expense	328	729	663	1,336
Cash payments	(1,107)	(1,528)	(2,287)	(3,016)
Balance at end of period	$ 20,557	$ 36,677	$ 20,557	$ 36,677

Balance Sheet Account Details - Narrative - Leases (Details) - USD ($) $ in Millions		6 Months Ended
	Apr. 05, 2016	Jul. 03, 2016
March 2016 Lease Agreements [Member]
Operating Leased Assets [Line Items]
Future minimum payments to be received under sublease		$ 51.2
Operating lease term		8 years
April 2016 Lease Agreements [Member]
Operating Leased Assets [Line Items]
Capital lease term	10 years
Future minimum payment due for lease addition in period	$ 127.4
Project construction costs incurred by landlord		$ 65.0

Balance Sheet Account Details - Narrative - Investment in Consolidated Variable Interest Entities (Details) - USD ($) shares in Millions		3 Months Ended		6 Months Ended
	Jul. 05, 2016	Jul. 03, 2016	Apr. 03, 2016	Jul. 03, 2016	Jan. 03, 2016	Jul. 31, 2015	Jun. 28, 2015	Dec. 28, 2014
Variable Interest Entity [Line Items]
Income Attributable to Illumina Stockholders for Earnings per Share		$ 1,600,000
Contributions from noncontrolling interest owners				$ 80,000,000
Cash and cash equivalents attributable to variable interest entities		951,662,000		951,662,000	$ 768,770,000		$ 591,057,000	$ 636,154,000
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents attributable to variable interest entities		$ 123,600,000		$ 123,600,000
GRAIL, Inc. [Member] \| Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Equity ownership interest percentage		52.00%		52.00%
Series A financing			$ 120,000,000.0
Amount contributed			40,000,000.0
Deemed dividend		$ 9,500,000
Deemed dividend, tax effect		$ 9,600,000
Contributions from noncontrolling interest owners			$ 80,000,000.0
Percentage of entity's losses absorbed		90.00%		90.00%
Helix Holdings I, LLC [Member] \| Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Equity ownership interest percentage		50.00%		50.00%		50.00%
Noncontrolling shareholders interest percentage		50.00%		50.00%
Subsequent Event [Member] \| GRAIL, Inc. [Member] \| Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Percentage of entity's losses absorbed	50.00%
GRAIL Class B [Member] \| GRAIL, Inc. [Member] \| Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Stock exchanged (in shares)			112.5
GRAIL Class A-1 Convertible [Member] \| GRAIL, Inc. [Member] \| Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Stock exchanged (in shares)		97.5
Illumina Class B [Member] \| GRAIL, Inc. [Member] \| Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Stock exchanged (in shares)		97.5

Balance Sheet Account Details - Summary of Activity of Redeemable Noncontrolling Interests (Details) $ in Thousands	6 Months Ended
	Jul. 03, 2016 USD ($)
Increase (Decrease) in Redeemable Noncontrolling Interests [Roll Forward]
Balance as of January 3, 2016	$ 32,546
Vesting of redeemable equity awards	1,031
Net loss attributable to noncontrolling interests	(5,270)
Adjustment up to the redemption value	5,426
Balance as of July 3, 2016	$ 33,733

Fair Value Measurements - Summary of Hierarchy for Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jul. 03, 2016	Jan. 03, 2016
Assets:
Available-for-sale securities	$ 473,594	$ 617,450
Debt securities in government sponsored entities [Member]
Assets:
Available-for-sale securities	18,113	14,626
Corporate debt securities [Member]
Assets:
Available-for-sale securities	325,754	421,094
U.S. Treasury securities [Member]
Assets:
Available-for-sale securities	129,727	181,730
Fair Value, Measurements, Recurring [Member]
Assets:
Deferred compensation plan assets	29,778	26,245
Total assets measured at fair value	1,186,078	1,034,941
Liabilities:
Acquisition related contingent consideration liabilities	5,300	35,000
Deferred compensation liability	27,791	24,925
Total liabilities measured at fair value	33,091	59,925
Fair Value, Measurements, Recurring [Member] \| Debt securities in government sponsored entities [Member]
Assets:
Available-for-sale securities	18,113	14,626
Fair Value, Measurements, Recurring [Member] \| Corporate debt securities [Member]
Assets:
Available-for-sale securities	325,754	421,094
Fair Value, Measurements, Recurring [Member] \| U.S. Treasury securities [Member]
Assets:
Available-for-sale securities	129,727	181,730
Fair Value, Measurements, Recurring [Member] \| Money market funds (cash equivalents) [Member]
Assets:
Money market funds (cash equivalents)	682,706	391,246
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Assets:
Total assets measured at fair value	812,433	572,976
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| U.S. Treasury securities [Member]
Assets:
Available-for-sale securities	129,727	181,730
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Money market funds (cash equivalents) [Member]
Assets:
Money market funds (cash equivalents)	682,706	391,246
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Assets:
Deferred compensation plan assets	29,778	26,245
Total assets measured at fair value	373,645	461,965
Liabilities:
Deferred compensation liability	27,791	24,925
Total liabilities measured at fair value	27,791	24,925
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Debt securities in government sponsored entities [Member]
Assets:
Available-for-sale securities	18,113	14,626
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Corporate debt securities [Member]
Assets:
Available-for-sale securities	325,754	421,094
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member]
Liabilities:
Acquisition related contingent consideration liabilities	5,300	35,000
Total liabilities measured at fair value	$ 5,300	$ 35,000

Fair Value Measurements - Narrative (Details) - Contingent Consideration Liability [Member] $ in Thousands	6 Months Ended
	Jul. 03, 2016 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Additional liability recorded as a result of a current period acquisition	$ 5,300
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	4.00%
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	6.00%

Fair Value Measurements - Summary of Changes in Estimated Fair Value of Contingent Consideration Liabilities (Details) - Contingent Consideration Liability [Member] $ in Thousands	6 Months Ended
	Jul. 03, 2016 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 35,000
Additional liability recorded as a result of a current period acquisition	5,300
Cash payments	(35,000)
Ending balance	$ 5,300

Debt - Narrative (Details) - Convertible Senior Notes [Member]	1 Months Ended	6 Months Ended
	Jun. 29, 2014 USD ($) $ / shares	Jul. 03, 2016 USD ($) day	Dec. 31, 2011 USD ($)
2019 Notes [Member]
Debt Instrument [Line Items]
Principal amount \| $	$ 632,500,000	$ 632,500,000
Interest rate on convertible senior notes		0.00%
Effective interest rate used to measure fair value of converted notes upon conversion	2.90%
Conversion rate	0.0039318
Conversion price (in dollars per share) \| $ / shares	$ 254.34
Threshold note trading days		5
Threshold consecutive note trading days		10 days
Threshold percentage of note price trigger		98.00%
Threshold common stock trading days		20
Threshold consecutive common stock trading days		30 days
Threshold percentage of common stock price trigger		130.00%
2021 Notes [Member]
Debt Instrument [Line Items]
Principal amount \| $	$ 517,500,000	$ 517,500,000
Interest rate on convertible senior notes		0.50%
Effective interest rate used to measure fair value of converted notes upon conversion	3.50%
Conversion rate	0.0039318
Conversion price (in dollars per share) \| $ / shares	$ 254.34
Threshold note trading days		5
Threshold consecutive note trading days		10 days
Threshold percentage of note price trigger		98.00%
Threshold common stock trading days		20
Threshold consecutive common stock trading days		30 days
Threshold percentage of common stock price trigger		130.00%
2016 Notes [Member]
Debt Instrument [Line Items]
Principal amount \| $			$ 920,000,000
Interest rate on convertible senior notes			0.25%
Effective interest rate used to measure fair value of converted notes upon conversion			4.50%

Debt - Summary of Conversion of 2016 Notes (Details) - Convertible Senior Notes [Member] - 2016 Notes [Member] shares in Thousands, $ in Thousands	6 Months Ended
	Jul. 03, 2016 USD ($) shares
Extinguishment of Debt [Line Items]
Cash paid for principal of notes converted	$ 75,543
Conversion value over principal amount paid in shares of common stock	$ 63,753
Number of shares of common stock issued upon conversion \| shares	409

Debt - Summary of Information about Equity and Liability Components of Convertible Senior Notes Outstanding (Details) - USD ($) $ in Thousands	6 Months Ended
	Jul. 03, 2016	Jun. 28, 2015	Jan. 03, 2016
Summarized information about equity and liability components of convertible senior notes
Less: current portion	$ (511)		$ (74,929)
Long-term debt	1,031,370		1,015,649
Convertible Senior Notes [Member]
Summarized information about equity and liability components of convertible senior notes
Principal amount of convertible notes outstanding	1,150,000		1,225,547
Unamortized discount of liability component	(120,077)		(134,969)
Net carrying amount of liability component	1,029,923		1,090,578
Less: current portion			(74,929)
Long-term debt	1,029,923		1,015,649
Carrying value of equity component, net of debt issuance cost	$ 161,237		213,811
Weighted-average remaining amortization period of discount on the liability component	4 years 1 month	4 years 7 months
Fair Value, Inputs, Level 2 [Member] \| Convertible Senior Notes [Member]
Summarized information about equity and liability components of convertible senior notes
Fair value of outstanding notes	$ 1,135,147		$ 1,456,451

Debt - Other (Details) - USD ($) $ in Thousands	Jul. 03, 2016	Jan. 03, 2016
Line of Credit Facility [Line Items]
Long-term debt, current portion	$ 511	$ 74,929
Long-term debt	1,031,370	$ 1,015,649
Helix Holdings I, LLC [Member] \| Line of Credit [Member]
Line of Credit Facility [Line Items]
Long-term debt, current portion	500
Long-term debt	$ 1,500

Share-based Compensation Expense - Summary of Share-based Compensation Expense for all Stock Awards (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 03, 2016	Jun. 28, 2015	Jul. 03, 2016	Jun. 28, 2015
Share-based Compensation
Share-based compensation expense before taxes	$ 31,970	$ 32,957	$ 67,262	$ 64,875
Related income tax benefits	(7,667)	(9,315)	(15,478)	(18,428)
Share-based compensation expense, net of taxes	24,303	23,642	51,784	46,447
Cost of product revenue [Member]
Share-based Compensation
Share-based compensation expense before taxes	1,958	2,113	4,150	4,445
Cost of service and other revenue [Member]
Share-based Compensation
Share-based compensation expense before taxes	421	466	853	745
Research and development [Member]
Share-based Compensation
Share-based compensation expense before taxes	10,693	10,747	21,374	22,054
Selling, general and administrative [Member]
Share-based Compensation
Share-based compensation expense before taxes	$ 18,898	$ 19,631	$ 40,885	$ 37,631

Share-based Compensation Expense - Summary of Assumptions used to Estimate the Weighted-Average Fair Value Per Share for Stock Purchase under the Employee Stock Purchase Plan (Details) - Employee Stock [Member]	6 Months Ended
	Jul. 03, 2016 $ / shares
Assumptions used to estimate the fair value per share of employee stock purchase rights granted
Risk-free interest rate	0.47%
Expected volatility, minimum	40.00%
Expected volatility, maximum	44.00%
Expected dividends	0.00%
Weighted-average fair value per share (in dollars per share)	$ 47.77
Minimum [Member]
Assumptions used to estimate the fair value per share of employee stock purchase rights granted
Expected term	6 months
Maximum [Member]
Assumptions used to estimate the fair value per share of employee stock purchase rights granted
Expected term	1 year

Share-based Compensation Expense - Narrative (Details) $ in Millions	6 Months Ended
	Jul. 03, 2016 USD ($)
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Unrecognized compensation cost related to stock options, restricted stock, and ESPP shares granted to date	$ 226.0
Weighted-average period of unrecognized compensation cost related to stock options, restricted stock, and ESPP shares granted to date	2 years

Stockholders' Equity - Narrative (Details) shares in Millions	Jul. 03, 2016 shares
2015 Illumina and 2005 Solexa Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for issuance (in shares)	7.6

Stockholders' Equity - Summary of Restricted Stock Activity and Related Information (Details) shares in Thousands	6 Months Ended
	Jul. 03, 2016 $ / shares shares
Restricted Stock Awards (RSA) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding at period start (in shares) \| shares	21
Awarded (in shares) \| shares	22
Outstanding at period end (in shares) \| shares	43
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted-Average Grant Date Fair Value per Share, Outstanding at period start (in dollars per share) \| $ / shares	$ 47.93
Weighted-Average Grant Date Fair Value per Share, Awarded (in dollars per share) \| $ / shares	179.00
Weighted-Average Grant Date Fair Value per Share, Outstanding at period end (in dollars per share) \| $ / shares	$ 114.59
Restricted Stock Units (RSU) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding at period start (in shares) \| shares	2,206
Awarded (in shares) \| shares	121
Vested (in shares) \| shares	(321)
Cancelled (in shares) \| shares	(153)
Outstanding at period end (in shares) \| shares	1,853
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted-Average Grant Date Fair Value per Share, Outstanding at period start (in dollars per share) \| $ / shares	$ 131.80
Weighted-Average Grant Date Fair Value per Share, Awarded (in dollars per share) \| $ / shares	154.96
Weighted-Average Grant Date Fair Value per Share, Vested (in dollars per share) \| $ / shares	82.91
Weighted-Average Grant Date Fair Value per Share, Cancelled (in dollars per share) \| $ / shares	135.36
Weighted-Average Grant Date Fair Value per Share, Outstanding at period end (in dollars per share) \| $ / shares	$ 141.46
Performance Stock Units (PSU) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding at period start (in shares) \| shares	583
Awarded (in shares) \| shares	12
Cancelled (in shares) \| shares	(97)
Outstanding at period end (in shares) \| shares	498
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted-Average Grant Date Fair Value per Share, Outstanding at period start (in dollars per share) \| $ / shares	$ 169.41
Weighted-Average Grant Date Fair Value per Share, Awarded (in dollars per share) \| $ / shares	164.66
Weighted-Average Grant Date Fair Value per Share, Cancelled (in dollars per share) \| $ / shares	163.06
Weighted-Average Grant Date Fair Value per Share, Outstanding at period end (in dollars per share) \| $ / shares	$ 170.54

Stockholders' Equity - Summary of Stock Option Activity Under all Stock Option Plans (Details) shares in Thousands	6 Months Ended
	Jul. 03, 2016 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, Outstanding at period start (in shares) \| shares	1,599
Options, Exercised (in shares) \| shares	(331)
Options, Cancelled (in shares) \| shares	(2)
Options, Outstanding at period end (in shares) \| shares	1,266
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-Average Exercise Price, Options, Outstanding at period start (in dollars per share) \| $ / shares	$ 41.95
Weighted-Average Exercise Price, Options, Exercised (in dollars per share) \| $ / shares	30.14
Weighted-Average Exercise Price, Options, Cancelled (in dollars per share) \| $ / shares	48.36
Weighted-Average Exercise Price, Options, Outstanding at period end (in dollars per share) \| $ / shares	$ 45.04

Stockholders' Equity - Narrative - Stock Options (Details) shares in Millions	Jul. 03, 2016 $ / shares shares
Equity [Abstract]
Stock options exercisable (in shares) \| shares	1.3
Stock options exercisable outstanding weighted-average exercise price per share (in dollars per share) \| $ / shares	$ 45.09

Stockholders' Equity - Narrative - Employee Stock Purchase Plan (Details) - Employee Stock [Member] shares in Millions	6 Months Ended
	Jul. 03, 2016 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Specified percentage of the fair market value of the common stock on the first or last day of the offering period whichever is lower at which stock is purchased	85.00%
Total shares issued under the ESPP (in shares)	0.1
Shares available for issuance (in shares)	14.4

Stockholders' Equity - Narrative - Share Repurchases (Details) - USD ($) $ in Thousands, shares in Millions	6 Months Ended
	Jul. 03, 2016	Jun. 28, 2015	Oct. 29, 2015	May 01, 2015
Class of Stock [Line Items]
Common stock repurchases	$ 100,000	$ 34,753
Common Stock [Member]
Class of Stock [Line Items]
Repurchase of common shares (in shares)	0.7
Common stock repurchases	$ 100,000
Additional amount authorized to repurchase	$ 156,100
Common Stock [Member] \| Rule 10b5-1 Share Repurchase Plan [Member]
Class of Stock [Line Items]
Stock repurchase program, authorized amount				$ 150,000
Common Stock [Member] \| October 2015 Share Repurchase Plan [Member]
Class of Stock [Line Items]
Stock repurchase program, authorized amount			$ 250,000

Income Taxes - Narrative (Details)	3 Months Ended	6 Months Ended
Income Taxes - Narrative (Details)	Jul. 03, 2016	Jul. 03, 2016
Income Tax Disclosure [Abstract]
Effective tax rate	25.90%	25.30%
U.S. federal statutory tax rate		35.00%

Legal Proceedings - Narrative (Details) $ in Millions	6 Months Ended
Legal Proceedings - Narrative (Details) $ in Millions	Jul. 03, 2016 USD ($)
Loss Contingencies [Line Items]
Litigation settlement amount	$ 21.0
Amortization period of intangible asset	7 years
Accrued legal contingencies	$ 21.0
Finite-Lived Intangible Assets [Member]
Loss Contingencies [Line Items]
Litigation settlement amount	11.5
Release Of Past Damages [Member]
Loss Contingencies [Line Items]
Litigation settlement amount	$ 9.5