Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2019	Apr. 29, 2019
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	CSLT
Entity Registrant Name	CASTLIGHT HEALTH, INC.
Entity Central Index Key	0001433714
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Small Business	false
Class A
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		35,117,853
Class B
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		108,842,540

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 66,338	$ 66,005
Marketable securities	0	11,327
Accounts receivable and other, net	34,699	26,816
Prepaid expenses and other current assets	4,351	3,680
Total current assets	105,388	107,828
Property and equipment, net	3,754	3,963
Restricted cash, non-current	1,325	1,325
Deferred commissions	19,067	20,142
Deferred professional service costs	9,672	10,133
Intangible assets, net	15,333	16,209
Goodwill	91,785	91,785
Operating lease right-of-use assets, net	15,989
Other assets	2,209	2,129
Total assets	264,522	253,514
Current liabilities:
Accounts payable	8,760	9,556
Accrued expenses and other current liabilities	13,025	15,454
Accrued compensation	5,005	5,975
Deferred revenue	23,774	20,193
Operating lease liabilities	5,928
Total current liabilities	56,492	51,178
Deferred revenue, non-current	944	1,030
Debt, non-current	2,789	3,254
Operating lease liabilities, non-current	13,428
Other liabilities, non-current	1,040	3,381
Total liabilities	74,693	58,843
Commitments and contingencies
Stockholders’ equity:
Common stock	14	14
Additional paid-in capital	615,394	609,697
Accumulated other comprehensive loss	0	0
Accumulated deficit	(425,579)	(415,040)
Total stockholders’ equity	189,829	194,671
Total liabilities and stockholders’ equity	$ 264,522	$ 253,514

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($)
shares in Thousands, $ in Thousands

3 Months Ended

Mar. 31, 2019

Mar. 31, 2018

Revenue:

Total revenue, net

$ 35,490

$ 36,479

Cost of revenue:

Total cost of revenue

14,110

14,943

Gross profit

21,380

21,536

Operating expenses:

Sales and marketing

^[1]

9,215

13,912

Research and development

^[1]

15,725

15,371

General and administrative

^[1]

7,293

6,825

Total operating expenses

32,233

36,108

Operating loss

(10,853)

(14,572)

Other income, net

314

128

Net loss

$ (10,539)

$ (14,444)

Net loss per share, basic and diluted (in usd per share)

$ (0.07)

$ (0.11)

Weighted-average shares used to compute basic and diluted net loss per share (in shares)

143,000

134,994

Subscription

Revenue:

Total revenue, net

$ 33,806

$ 32,989

Cost of revenue:

Total cost of revenue

^[1]

8,166

9,174

Professional services and other

Revenue:

Total revenue, net

1,684

3,490

Cost of revenue:

Total cost of revenue

^[1]

$ 5,944

$ 5,769

[1]	Includes stock-based compensation expense as follows: Three Months Ended March 31, 2019 2018Cost of revenue: Cost of subscription$219 $242Cost of professional services and other265 301Sales and marketing627 1,138Research and development1,704 1,654General and administrative1,162 1,257

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Subscription
Stock-based compensation expense	$ 219	$ 242
Professional services and other
Stock-based compensation expense	265	301
Sales and marketing
Stock-based compensation expense	627	1,138
Research and development
Stock-based compensation expense	1,704	1,654
General and administrative
Stock-based compensation expense	$ 1,162	$ 1,257

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net loss	$ (10,539)	$ (14,444)
Other comprehensive income:
Net change in unrealized gain on available-for-sale marketable securities	0	2
Other comprehensive income	0	2
Comprehensive loss	$ (10,539)	$ (14,442)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Class A and B Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2017		134,539,275
Beginning balance at Dec. 31, 2017	$ 211,557	$ 13	$ 586,900	$ (22)	$ (375,334)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		747,311
Exercise of stock options, net (in shares)		309,242
Exercise of stock options, net	490		490
Stock-based compensation	4,633		4,633
Comprehensive loss	(14,442)			2	(14,444)
Ending balance (in shares) at Mar. 31, 2018		135,595,828
Ending balance at Mar. 31, 2018	202,238	$ 13	592,023	(20)	(389,778)
Beginning balance (in shares) at Dec. 31, 2018		141,927,205
Beginning balance at Dec. 31, 2018	$ 194,671	$ 14	609,697	0	(415,040)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		967,712
Exercise of stock options, net (in shares)	1,060,870	1,060,870
Exercise of stock options, net	$ 1,680		1,680
Stock-based compensation	4,017		4,017
Comprehensive loss	(10,539)			0	(10,539)
Ending balance (in shares) at Mar. 31, 2019		143,955,787
Ending balance at Mar. 31, 2019	$ 189,829	$ 14	$ 615,394	$ 0	$ (425,579)

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating activities:
Net loss	$ (10,539)	$ (14,444)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,344	1,860
Stock-based compensation	3,977	4,592
Amortization and impairment of deferred commissions	2,491	2,853
Amortization and impairment of deferred professional service costs	969	946
Non-cash operating lease expense	1,282	0
Lease exit and related charges	0	916
Accretion and amortization of marketable securities	(126)	(131)
Changes in operating assets and liabilities:
Accounts receivable and other, net	(7,883)	(11,196)
Deferred commissions	(1,416)	(1,171)
Deferred professional service costs	(469)	(742)
Prepaid expenses and other assets	(751)	206
Accounts payable	(849)	1,783
Operating lease liabilities	(1,382)	0
Accrued expenses and other liabilities	(1,304)	(1,237)
Deferred revenue	3,495	3,183
Accrued compensation	(970)	(6,390)
Net cash used in operating activities	(12,131)	(18,972)
Investing activities:
Purchase of property and equipment	(204)	(388)
Purchase of marketable securities	0	(10,025)
Maturities of marketable securities	11,453	15,750
Net cash provided by investing activities	11,249	5,337
Financing activities:
Proceeds from exercise of stock options	1,680	490
Principal payments on long-term debt	(465)	0
Net cash provided by financing activities	1,215	490
Net increase (decrease) in cash, cash equivalents and restricted cash	333	(13,145)
Cash, cash equivalents and restricted cash at beginning of period	67,330	62,644
Cash, cash equivalents and restricted cash at end of period	67,663	49,499
Reconciliation of cash, cash equivalents and restricted cash:
Total cash, cash equivalents and restricted cash	$ 67,330	$ 62,644

Organization and Description of Business	3 Months Ended
Organization and Description of Business	Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Description of Business	Organization and Description of Business Castlight Health, Inc. (“Castlight” or “the Company”) offers a comprehensive software-as-a-service platform that simplifies health benefits navigation for millions of employees. The Castlight platform matches employees to the best resources their employers make available to them, whether they are healthy, actively seeking medical care, or managing a condition, and motivates them to take the best steps for their health. Castlight helps employers generate more value from their benefits investments by helping to improve outcomes, lower health care costs, and increase benefits satisfaction. The Company was incorporated in the State of Delaware in January 2008. The Company's principal executive offices are located in San Francisco, California.

Accounting Standards and Significant Accounting Policies

3 Months Ended

Mar. 31, 2019

Accounting Policies [Abstract]

Accounting Standards and Significant Accounting Policies

Basis of Presentation and Principles of Consolidation

The accompanying unaudited condensed consolidated financial statements include Castlight and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. In the opinion of management, the information herein reflects all adjustments, consisting only of normal recurring adjustments except as otherwise noted, considered necessary for a fair statement of results of operations, financial position, stockholders’ equity and cash flows. The results for the interim periods presented are not necessarily indicative of the results expected for any future period. The following information should be read in conjunction with the audited financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018.

Other than described below, there have been no changes to our significant accounting policies described in our Annual Report that have had a material impact on our consolidated financial statements and related notes.

Use of Estimates

The preparation of condensed consolidated financial statements in conformity with GAAP requires the Company to make certain estimates, judgments and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements, as well as the reported amounts of revenue and expenses during the reporting period. These estimates include, but are not limited to the determination of:

•Variable consideration included in the transaction price of the Company’s contracts with customers;

•The standalone selling price of the performance obligations in the Company’s contracts with customers;

•Assumptions used in the valuation of certain equity awards;

•The amortization period for deferred commissions and deferred professional services costs; and


•	Assumptions used in the calculation of right-of-use (“ROU”) assets and lease liabilities for operating leases, including lease terms and the Company’s incremental borrowing rate.

Actual results could differ from those estimates, and such differences could be material to the Company’s consolidated financial position and results of operations.

Summary of Significant Accounting Policies

Leases

The Company determines if an arrangement is a lease and its classification at lease inception. Operating lease liabilities are recognized at the commencement date of the lease based on the present value of lease payments over the lease term. The Company uses its incremental borrowing rate based on the information available at the lease commencement date to compute the present value of lease payments when the implicit rate is not readily determinable. ROU assets are measured at lease inception based on the initial measurement of the lease liability, plus any prepaid lease amounts, less any lease incentives. The Company does not recognize ROU assets or lease liabilities for leases with a term of 12 months or less. Lease terms do not include options to extend or terminate the lease unless it is reasonably certain that the option will be exercised. Generally, lease expense for lease payments is recognized on a straight-line basis over the lease term. The Company's lease agreements have both lease and non-lease components. The Company has elected to account for the non-lease components of its leases as part of their related lease components.

Concentrations of Risk and Significant Customers

No single direct customer accounted for more than 10% of total revenue or accounts receivable for the three months ended March 31, 2019. Castlight had one channel partner that represented approximately 24% of total revenue for three months ended March 31, 2019, and approximately 23% of accounts receivable as of March 31, 2019.

Recently Adopted Accounting Pronouncements

Effective January 1, 2019, the Company adopted Accounting Standards Update (“ASU”) 2016-02, Leases, and subsequent amendments ("ASC 842") using the modified retrospective method, and chose to apply the provisions at the beginning of the period of adoption. The guidance requires lessees to put all leases that have a term of more than one year on their balance sheets, whether operating or financing, while continuing to recognize the expenses on their income statements. The guidance states that a lessee would recognize a lease liability for the obligation to make lease payments and a right-of-use ("ROU") asset for the right to use the underlying asset for the lease term.

As a result of the adoption of ASC 842 as of January 1, 2019, reporting periods beginning on and after January 1, 2019 are presented under ASC 842, while prior period amounts were not adjusted and continue to be reported in accordance with prior accounting guidance under ASC 840. In addition, the Company elected the package of practical expedients permitted under the transition guidance within the new standard, which among other things, allowed the Company to carry forward the historical lease classification. As a result of the adoption of the new lease accounting guidance, the Company recognized on January 1, 2019 an operating lease ROU asset of approximately $17.3 million and an operating lease liability of approximately $20.7 million. The difference between the operating lease ROU asset and lease liability resulted from the reclass of the deferred rent liability to the operating lease ROU asset. The standard did not materially impact the Company’s condensed consolidated statement of operations and had no impact on the cash flows. See Note 10 - Leases for more information on leases.

Recently Issued Accounting Pronouncements

The Company considers the applicability and impact of all ASUs issued by the FASB. The Company determined that the ASUs issued by the FASB in the first quarter of 2019 are either not applicable or are expected to have minimal impact on the Company's condensed consolidated financial results.

Revenue, Deferred Revenue, Contract Balances and Performance Obligations	3 Months Ended
	Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
Revenue, Deferred Revenue, Contract Balances and Performance Obligations	Revenue, Deferred Revenue, Contract Balances and Performance Obligations The Company sells to customers based in the United States through direct sales and indirect channels. Indirect channel revenue represented approximately 26% and 10% of the Company’s total revenue for the three months ended March 31, 2019 and 2018, respectively. Deferred revenue as of March 31, 2019 and December 31, 2018 was $24.7 million and $21.2 million, respectively. Contract assets as of March 31, 2019 and December 31, 2018 were $1.2 million and $1.0 million, respectively. $11.2 million and $15.9 million of revenue was recognized during the three months ended March 31, 2019 and 2018, respectively, that was included in the Company’s deferred revenue balances at the beginning of the respective periods. The Company recorded favorable cumulative catch-up adjustments to revenue arising from changes in estimates of transaction price of $1.4 million during the three months ended March 31, 2019. Cumulative catch-up adjustments arising from changes in estimates of transaction price were immaterial during the three months ended March 31, 2018. The aggregate balance of remaining performance obligations from non-cancelable contracts with customers as of March 31, 2019 was $145.4 million. The Company expects to recognize approximately 70% of this balance over the next 12 months, with the remaining balance recognized thereafter. Remaining performance obligations are defined as deferred revenue and amounts yet to be billed for the non-cancelable portion of contracts.

Deferred Costs

3 Months Ended

Mar. 31, 2019

Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]

Deferred Costs

Changes in the balance of total deferred commissions and total deferred professional service costs during the three months ended March 31, 2019 are as follows (in thousands):



	As of December 31, 2018				Expense recognized			As of March 31, 2019
	As of December 31, 2018		Additions		Expense recognized			As of March 31, 2019
Deferred commissions	$	20,142	$	1,416	$	(2,491	)	$	19,067
Deferred professional service costs	10,133		508		(969		)	9,672
Total deferred commissions and professional service costs	$	30,275	$	1,924	$	(3,460	)	$	28,739

These costs are reviewed for impairment periodically, and no material impairment charges were recorded for the three months ended March 31, 2019 and 2018.

Goodwill and Intangible Assets

3 Months Ended

Mar. 31, 2019

Goodwill and Intangible Assets Disclosure [Abstract]

Goodwill and Intangible Assets

Goodwill

Currently, all of the Company’s goodwill relates to the acquisition of Jiff. The excess of purchase consideration over the fair value of net tangible and identifiable intangible assets acquired was recorded as goodwill. There were no changes to goodwill for the three months ended March 31, 2019.

Intangible assets, net

The following tables set forth the fair value components of identifiable acquired intangible assets (dollars in thousands):



	March 31, 2019
	Useful Life			Gross		Accumulated Amortization			Net
Customer relationships	10			$	10,900	$	(2,180	)	$	8,720
Developed technology	5			10,600		(4,240		)	6,360
Backlog	3			1,500		(1,314		)	186
Other acquired intangible assets	1	-	3	900		(833		)	67
Total identifiable intangible assets				$	23,900	$	(8,567	)	$	15,333



	December 31, 2018
	Useful Life			Gross		Accumulated Amortization			Net
Customer relationships	10			$	10,900	$	(1,908	)	$	8,992
Developed technology	5			10,600		(3,710		)	6,890
Backlog	3			1,500		(1,256		)	244
Other acquired intangible assets	1	-	3	900		(817		)	83
Total identifiable intangible assets				$	23,900	$	(7,691	)	$	16,209

Amortization expense from acquired intangible assets for the three months ended March 31, 2019 and 2018 was $0.9 million and $1.1 million, respectively. Amortization expense is included in cost of subscription, sales and marketing, and general and administrative expenses.

Estimated amortization expense for acquired intangible assets for the following five years and thereafter is as follows (in thousands):



Remainder of 2019	$	2,629
2020	3,242
2021	3,210
2022	1,620
2023	1,090
Thereafter	3,542
Total estimated amortization expense	$	15,333

Marketable Securities

3 Months Ended

Mar. 31, 2019

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

All of the Company’s cash equivalents and marketable securities are classified as “available-for-sale” securities. These securities are reported at fair value, with the related unrealized gains and losses included in accumulated other comprehensive income, a component of stockholders’ equity, except for money market mutual funds, where gains and losses are included in the results of operation.

As of March 31, 2019 and December 31, 2018, respectively, marketable securities consisted of the following (in thousands):



	As of March 31, 2019
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
U.S. treasury securities	$	3,138	$	—	$	—	$	3,138
U.S. agency obligations	16,706		—		—		16,706
Money market mutual funds	7,623		—		—		7,623
Included in cash and cash equivalents	$	27,467	$	—	$	—	$	27,467



	As of December 31, 2018
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
U.S. treasury securities	$	7,980	$	—	$	—	$	7,980
U.S. agency obligations	18,158		—		—		18,158
Money market mutual funds	7,115		—		—		7,115
	33,253		—		—		33,253
Included in cash and cash equivalents	21,926		—		—		21,926
Included in marketable securities	$	11,327	$	—	$	—	$	11,327

Fair Value Measurements

3 Months Ended

Mar. 31, 2019

Fair Value Disclosures [Abstract]

Fair Value Measurements

The Company measures its financial assets and liabilities at fair value at each reporting period using a fair value hierarchy that requires that the Company maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. A financial instrument’s classification within the fair value hierarchy is based upon the lowest level of input that is significant to the fair value measurement. Three levels of inputs may be used to measure fair value:

Level 1—Observable inputs that reflect quoted prices (unadjusted) for identical assets or liabilities in active markets.

Level 2—Include other inputs that are directly or indirectly observable in the marketplace.

Level 3—Unobservable inputs that are supported by little or no market activity.

The fair value of marketable securities included in the Level 2 category is based on observable inputs, such as quoted prices for similar assets at the measurement date; quoted prices in markets that are not active; or other inputs that are observable, either directly or indirectly. These values were obtained from a third-party pricing service and were evaluated using pricing models that vary by asset class and may incorporate available trade, bid and other market information and price quotes from well-established third party pricing vendors and broker-dealers.

There have been no changes in valuation techniques in the periods presented. There were no significant transfers between fair value measurement levels as of March 31, 2019 and December 31, 2018. As of March 31, 2019 and December 31, 2018, there were no securities within Level 3 of the fair value hierarchy.

The following tables present information about the Company’s assets and liabilities that are measured at fair value on a recurring basis using the above input categories (in thousands):



	As of March 31, 2019
	Level 1		Level 2		Total
Cash equivalents:
U.S. agency obligations	$	—	$	16,706	$	16,706
U.S. treasury securities	—		3,138		3,138
Money market mutual funds	7,623		—		7,623
	$	7,623	$	19,844	$	27,467



	As of December 31, 2018
	Level 1		Level 2		Total
Cash equivalents:
U.S. agency obligations	$	—	$	14,811	$	14,811
Money market mutual funds	7,115		—		7,115
Marketable securities:
U.S. treasury securities	—		7,980		7,980
U.S. agency obligations	—		3,347		3,347
	$	7,115	$	26,138	$	33,253

Gross unrealized gains and losses for cash equivalents and marketable securities as of March 31, 2019 and December 31, 2018 were not material. The Company does not believe the unrealized losses represent other-than-temporary impairments based on the Company’s evaluation of available evidence as of March 31, 2019 and December 31, 2018.

There were no realized gains or losses during the three months ended March 31, 2019. Marketable securities on the balance sheets consist of securities with original or remaining maturities at the time of purchase of greater than three months, and the remainder of the securities is reflected in cash and cash equivalents. All of the Company’s securities as of March 31, 2019 and December 31, 2018 mature within one year.

- 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

Property and Equipment

3 Months Ended

Mar. 31, 2019

Property, Plant and Equipment [Abstract]

Property and Equipment

Property and equipment consisted of the following (in thousands):



	As of
	March 31, 2019			December 31, 2018
Leasehold improvements	$	3,102		$	3,102
Computer equipment	6,931			6,860
Software	1,097			1,097
Internal-use software	2,925			2,925
Furniture and equipment	1,072			1,018
Total	15,127			15,002
Accumulated depreciation	(11,373		)	(11,039		)
Property and equipment, net	$	3,754		$	3,963

Depreciation and amortization expense for the three months ended March 31, 2019 and 2018 was $0.5 million and $0.7 million, respectively. Depreciation and amortization are recorded on a straight-line basis.

Debt

3 Months Ended

Mar. 31, 2019

Debt Disclosure [Abstract]

Debt

Term Loan

In connection with the Company’s acquisition of Jiff, on April 3, 2017, the Company, Jiff and Silicon Valley Bank (the “Bank”) agreed to refinance the existing term loan facility owed by Jiff to the Bank (the “Loan Agreement”) for approximately $5.6 million (the “Term Loan”). The Term Loan requires interest-only payments for the period May 2017 through September 2018, followed by 36 monthly payments of principal and interest. Obligations under the Term Loan accrue interest at a floating per annum rate equal to the greater of (A) the prime rate as published in the money rates section of The Wall Street Journal (“Prime Rate”) minus 1% or (B) 0%. Interest on the Term Loan is payable monthly. The maturity date of the Term Loan is September 1, 2021.

In addition to principal and interest payments, the Company is also required to pay $0.5 million as final payment on the earlier of maturity, termination or prepayment of the Term Loan. The Company accrues for the final payment over the life of the Term Loan using the effective interest method.

The future maturities of the Term Loan by year as of March 31, 2019 are as follows (in thousands):



Remainder of 2019	$	1,394
2020	1,859
2021⁽¹⁾	1,395
Total future maturities of debt	$	4,648
Less current maturities⁽²⁾	(1,859		)
Debt, non-current	$	2,789

⁽¹⁾Excludes the $0.5 million required to be paid as final payment on the earlier of maturity, termination or prepayment of the Term Loan.

⁽²⁾ Classified within accrued expenses and other current liabilities on the condensed consolidated balance sheet as of March 31, 2019.

Revolving Line of Credit

The Loan Agreement also provides for an up to $25 million revolving credit facility (the “Revolving Line”). As of March 31, 2019, no borrowings have been made under the Revolving Line. The Revolving Line expired on April 3, 2019, its termination date.

In relation to the Loan Agreement, the Company is subject to certain financial and reporting covenants. As of March 31, 2019, none of the financial covenants, which require the Company to maintain a certain minimum liquidity ratio, are applicable. The Company was in compliance with all reporting covenants in the Loan Agreement related to the outstanding principal balance as of March 31, 2019.

Leases

3 Months Ended

Mar. 31, 2019

Leases [Abstract]

Leases

The Company’s principal commitments primarily consist of obligations under leases for office space and co-location facilities for data center capacity. The leases expire at various dates through 2025 and, in some cases, include renewal options. The exercise of the option is at the sole discretion of the Company. The Company subleases certain office facilities to third parties. These leases are classified as operating leases. The Company does not have any short-term or finance leases. Information about these operating leases is disclosed in the following table (dollars in thousands):



	Three Months Ended March 31, 2019
Lease cost:
Operating lease cost	$	1,649
Variable lease cost ⁽¹⁾	151
Sublease income	(616		)
Total lease cost	$	1,184

Other information:
Operating cash flows used in the measurement of operating lease liabilities	$	1,749
Weighted-average remaining lease term - operating leases (in years)	3.5
Weighted-average discount rate - operating leases	7.45		%

⁽¹⁾Includes variable payments such as common area maintenance, property taxes and insurance.

Maturities of Lease Liabilities

As of March 31, 2019, the future minimum lease payments under non-cancellable operating leases are as follows (in thousands):



Remainder of 2019	$	5,336
2020	6,524
2021	5,355
2022	3,050
2023	677
2024 and later	1,111
Total lease payments	22,053
Less: Interest	(2,697		)
Present value of lease liabilities	$	19,356
Less: current portion	(5,928		)
Operating lease liabilities, non-current	$	13,428

Contingencies	3 Months Ended
Contingencies	Mar. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Contingencies	Contingencies Legal Matters From time to time, the Company may become subject to other legal proceedings, claims or litigation arising in the ordinary course of business. In addition, the Company may receive letters alleging infringement of patents or other intellectual property rights. If an unfavorable outcome were to occur in litigation, the impact could be material to the Company’s business, financial condition, cash flow or results of operations, depending on the specific circumstances of the outcome. The Company accrues for loss contingencies when it is both probable that it will incur the loss and when it can reasonably estimate the amount of the loss or range of loss.

Stock Compensation

3 Months Ended

Mar. 31, 2019

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

Stock Compensation

Restricted Stock Units

A summary of restricted stock unit activity for the three months ended March 31, 2019 is as follows:



	Number of Shares Outstanding		Weighted- Average Grant Date Fair Value
Balance as of December 31, 2018	9,528,602		$	3.54
Restricted Stock Units granted	1,189,450		$	3.40
Restricted Stock Units vested	(967,712	)	$	3.89
Restricted Stock Units forfeited and canceled ⁽¹⁾	(655,982	)	$	3.54
Balance as of March 31, 2019	9,094,358		$	3.48

⁽¹⁾ Includes PSUs that were granted in the prior year, which were canceled because performance targets were not achieved.

As of March 31, 2019, there was a total of $29.1 million in unrecognized compensation cost related to restricted stock units and performance stock units, which is expected to be recognized over a weighted-average period of approximately 2.7 years.

Stock Options

A summary of stock option activity for the three months ended March 31, 2019 is as follows:



	Options Outstanding		Weighted- Average Exercise Price		Aggregate Intrinsic Value (in thousands)
Balance as of December 31, 2018	6,265,223		$	2.65	$	3,499
Stock option grants	200,000		$	3.22
Stock options exercised	(1,060,870	)	$	1.58
Stock options forfeited and canceled	(21,987	)	$	3.04
Balance as of March 31, 2019	5,382,366		$	2.88	$	8,811

The total grant-date fair value of stock options granted during the three months ended March 31, 2019 and 2018 was $0.4 million and $0.3 million, respectively.

The fair value of each option grant was estimated on the date of grant using the Black-Scholes option-valuation model with the following assumptions and fair value per share:



	Three Months Ended March 31, 2019
	2019	2018
Volatility	57%	57%
Expected life (in years)	6.06	6.06
Risk-free interest rate	2.57%	2.72	%	-	2.74%
Dividend yield	—%	—%

As of March 31, 2019, the Company had $1.2 million in unrecognized compensation cost related to non-vested stock options, which is expected to be recognized over a weighted-average period of approximately 2.5 years.

Stockholders' Equity	3 Months Ended
Stockholders' Equity	Mar. 31, 2019
Equity [Abstract]
Stockholders’ Equity	Stockholders’ Equity Common Stock As of March 31, 2019, the Company had 36,137,783 shares of Class A common stock and 107,818,004 shares of Class B common stock outstanding.

Income Taxes	3 Months Ended
Income Taxes	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The effective tax rate for each of the three month periods ended March 31, 2019 and 2018 was zero percent, primarily as a result of the estimated tax loss for the year and the change in valuation allowance. At March 31, 2019, all unrecognized tax benefits are subject to a full valuation allowance and, if recognized, will not affect the effective tax rate.

Net Loss per Share

3 Months Ended

Mar. 31, 2019

Earnings Per Share [Abstract]

Net Loss per Share

Basic net loss per share is computed by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period. Diluted net loss per share is computed by giving effect to all potential shares of common stock, including Preferred Stock and outstanding stock options and warrants, to the extent dilutive. Basic and diluted net loss per share was the same for each period presented as the inclusion of all potential shares of common stock outstanding would have been anti-dilutive.

Net loss is allocated based on the contractual participation rights of the Class A and Class B common stock as if the earnings for the year have been distributed. As the liquidation and dividend rights are identical, the net loss is allocated on a proportionate basis.

The following table presents the calculation of basic and diluted net loss per share for the Company’s common stock (in thousands, except per share data):



	Three Months Ended March 31,
	2019						2018
	Class A			Class B			Class A			Class B
Net loss	$	(2,741	)	$	(7,798	)	$	(5,646	)	$	(8,798	)
Weighted-average shares used to compute basic and diluted net loss per share	37,189			105,811			52,764			82,230
Basic and diluted net loss per share	$	(0.07	)	$	(0.07	)	$	(0.11	)	$	(0.11	)

The following securities were excluded from the calculation of diluted net loss per share for common stock because their effect would have been anti-dilutive for the periods presented (in thousands):



	Three Months Ended March 31,
	2019	2018
Stock options and restricted stock units	14,477	20,601
Warrants	115	115
Total	14,592	20,716

Accounting Standards and Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2019

Accounting Policies [Abstract]

Basis of Presentation and Principles of Consolidation

The accompanying unaudited condensed consolidated financial statements include Castlight and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. In the opinion of management, the information herein reflects all adjustments, consisting only of normal recurring adjustments except as otherwise noted, considered necessary for a fair statement of results of operations, financial position, stockholders’ equity and cash flows. The results for the interim periods presented are not necessarily indicative of the results expected for any future period. The following information should be read in conjunction with the audited financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018.

Other than described below, there have been no changes to our significant accounting policies described in our Annual Report that have had a material impact on our consolidated financial statements and related notes.

Use of Estimates

The preparation of condensed consolidated financial statements in conformity with GAAP requires the Company to make certain estimates, judgments and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements, as well as the reported amounts of revenue and expenses during the reporting period. These estimates include, but are not limited to the determination of:

•Variable consideration included in the transaction price of the Company’s contracts with customers;

•The standalone selling price of the performance obligations in the Company’s contracts with customers;

•Assumptions used in the valuation of certain equity awards;

•The amortization period for deferred commissions and deferred professional services costs; and


•	Assumptions used in the calculation of right-of-use (“ROU”) assets and lease liabilities for operating leases, including lease terms and the Company’s incremental borrowing rate.

Actual results could differ from those estimates, and such differences could be material to the Company’s consolidated financial position and results of operations.

Leases

The Company determines if an arrangement is a lease and its classification at lease inception. Operating lease liabilities are recognized at the commencement date of the lease based on the present value of lease payments over the lease term. The Company uses its incremental borrowing rate based on the information available at the lease commencement date to compute the present value of lease payments when the implicit rate is not readily determinable. ROU assets are measured at lease inception based on the initial measurement of the lease liability, plus any prepaid lease amounts, less any lease incentives. The Company does not recognize ROU assets or lease liabilities for leases with a term of 12 months or less. Lease terms do not include options to extend or terminate the lease unless it is reasonably certain that the option will be exercised. Generally, lease expense for lease payments is recognized on a straight-line basis over the lease term. The Company's lease agreements have both lease and non-lease components. The Company has elected to account for the non-lease components of its leases as part of their related lease components.

Recently Adopted Accounting Pronouncements and Recently Issued Accounting Pronouncements

Recently Adopted Accounting Pronouncements

Effective January 1, 2019, the Company adopted Accounting Standards Update (“ASU”) 2016-02, Leases, and subsequent amendments ("ASC 842") using the modified retrospective method, and chose to apply the provisions at the beginning of the period of adoption. The guidance requires lessees to put all leases that have a term of more than one year on their balance sheets, whether operating or financing, while continuing to recognize the expenses on their income statements. The guidance states that a lessee would recognize a lease liability for the obligation to make lease payments and a right-of-use ("ROU") asset for the right to use the underlying asset for the lease term.

As a result of the adoption of ASC 842 as of January 1, 2019, reporting periods beginning on and after January 1, 2019 are presented under ASC 842, while prior period amounts were not adjusted and continue to be reported in accordance with prior accounting guidance under ASC 840. In addition, the Company elected the package of practical expedients permitted under the transition guidance within the new standard, which among other things, allowed the Company to carry forward the historical lease classification. As a result of the adoption of the new lease accounting guidance, the Company recognized on January 1, 2019 an operating lease ROU asset of approximately $17.3 million and an operating lease liability of approximately $20.7 million. The difference between the operating lease ROU asset and lease liability resulted from the reclass of the deferred rent liability to the operating lease ROU asset. The standard did not materially impact the Company’s condensed consolidated statement of operations and had no impact on the cash flows. See Note 10 - Leases for more information on leases.

Recently Issued Accounting Pronouncements

The Company considers the applicability and impact of all ASUs issued by the FASB. The Company determined that the ASUs issued by the FASB in the first quarter of 2019 are either not applicable or are expected to have minimal impact on the Company's condensed consolidated financial results.

Deferred Costs (Tables)

3 Months Ended

Mar. 31, 2019

Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]

Changes in Balance of Total Deferred Commissions and Total Deferred Professional Service Costs

Changes in the balance of total deferred commissions and total deferred professional service costs during the three months ended March 31, 2019 are as follows (in thousands):



	As of December 31, 2018				Expense recognized			As of March 31, 2019
	As of December 31, 2018		Additions		Expense recognized			As of March 31, 2019
Deferred commissions	$	20,142	$	1,416	$	(2,491	)	$	19,067
Deferred professional service costs	10,133		508		(969		)	9,672
Total deferred commissions and professional service costs	$	30,275	$	1,924	$	(3,460	)	$	28,739

Goodwill and Intangible Assets (Tables)

3 Months Ended

Mar. 31, 2019

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of Finite-Lived Intangible Assets

The following tables set forth the fair value components of identifiable acquired intangible assets (dollars in thousands):



	March 31, 2019
	Useful Life			Gross		Accumulated Amortization			Net
Customer relationships	10			$	10,900	$	(2,180	)	$	8,720
Developed technology	5			10,600		(4,240		)	6,360
Backlog	3			1,500		(1,314		)	186
Other acquired intangible assets	1	-	3	900		(833		)	67
Total identifiable intangible assets				$	23,900	$	(8,567	)	$	15,333



	December 31, 2018
	Useful Life			Gross		Accumulated Amortization			Net
Customer relationships	10			$	10,900	$	(1,908	)	$	8,992
Developed technology	5			10,600		(3,710		)	6,890
Backlog	3			1,500		(1,256		)	244
Other acquired intangible assets	1	-	3	900		(817		)	83
Total identifiable intangible assets				$	23,900	$	(7,691	)	$	16,209

Schedule of Finite-Lived Intangible Assets, Future Amortization Expense

Estimated amortization expense for acquired intangible assets for the following five years and thereafter is as follows (in thousands):



Remainder of 2019	$	2,629
2020	3,242
2021	3,210
2022	1,620
2023	1,090
Thereafter	3,542
Total estimated amortization expense	$	15,333

Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2019

Investments, Debt and Equity Securities [Abstract]

Available-for-sale Securities

As of March 31, 2019 and December 31, 2018, respectively, marketable securities consisted of the following (in thousands):



	As of March 31, 2019
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
U.S. treasury securities	$	3,138	$	—	$	—	$	3,138
U.S. agency obligations	16,706		—		—		16,706
Money market mutual funds	7,623		—		—		7,623
Included in cash and cash equivalents	$	27,467	$	—	$	—	$	27,467



	As of December 31, 2018
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
U.S. treasury securities	$	7,980	$	—	$	—	$	7,980
U.S. agency obligations	18,158		—		—		18,158
Money market mutual funds	7,115		—		—		7,115
	33,253		—		—		33,253
Included in cash and cash equivalents	21,926		—		—		21,926
Included in marketable securities	$	11,327	$	—	$	—	$	11,327

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2019

Fair Value Disclosures [Abstract]

Fair Value, Assets Measured on Recurring Basis

The following tables present information about the Company’s assets and liabilities that are measured at fair value on a recurring basis using the above input categories (in thousands):



	As of March 31, 2019
	Level 1		Level 2		Total
Cash equivalents:
U.S. agency obligations	$	—	$	16,706	$	16,706
U.S. treasury securities	—		3,138		3,138
Money market mutual funds	7,623		—		7,623
	$	7,623	$	19,844	$	27,467



	As of December 31, 2018
	Level 1		Level 2		Total
Cash equivalents:
U.S. agency obligations	$	—	$	14,811	$	14,811
Money market mutual funds	7,115		—		7,115
Marketable securities:
U.S. treasury securities	—		7,980		7,980
U.S. agency obligations	—		3,347		3,347
	$	7,115	$	26,138	$	33,253

Property and Equipment (Tables)

3 Months Ended

Mar. 31, 2019

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment

Property and equipment consisted of the following (in thousands):



	As of
	March 31, 2019			December 31, 2018
Leasehold improvements	$	3,102		$	3,102
Computer equipment	6,931			6,860
Software	1,097			1,097
Internal-use software	2,925			2,925
Furniture and equipment	1,072			1,018
Total	15,127			15,002
Accumulated depreciation	(11,373		)	(11,039		)
Property and equipment, net	$	3,754		$	3,963

Debt (Tables)

3 Months Ended

Mar. 31, 2019

Debt Disclosure [Abstract]

Schedule of Maturities of Long-term Debt

The future maturities of the Term Loan by year as of March 31, 2019 are as follows (in thousands):



Remainder of 2019	$	1,394
2020	1,859
2021⁽¹⁾	1,395
Total future maturities of debt	$	4,648
Less current maturities⁽²⁾	(1,859		)
Debt, non-current	$	2,789

⁽¹⁾Excludes the $0.5 million required to be paid as final payment on the earlier of maturity, termination or prepayment of the Term Loan.

⁽²⁾ Classified within accrued expenses and other current liabilities on the condensed consolidated balance sheet as of March 31, 2019.

Leases (Tables)

3 Months Ended

Mar. 31, 2019

Leases [Abstract]

Information About Operating Leases

Information about these operating leases is disclosed in the following table (dollars in thousands):



	Three Months Ended March 31, 2019
Lease cost:
Operating lease cost	$	1,649
Variable lease cost ⁽¹⁾	151
Sublease income	(616		)
Total lease cost	$	1,184

Other information:
Operating cash flows used in the measurement of operating lease liabilities	$	1,749
Weighted-average remaining lease term - operating leases (in years)	3.5
Weighted-average discount rate - operating leases	7.45		%

⁽¹⁾Includes variable payments such as common area maintenance, property taxes and insurance.

Maturities of Lease Liabilities

As of March 31, 2019, the future minimum lease payments under non-cancellable operating leases are as follows (in thousands):



Remainder of 2019	$	5,336
2020	6,524
2021	5,355
2022	3,050
2023	677
2024 and later	1,111
Total lease payments	22,053
Less: Interest	(2,697		)
Present value of lease liabilities	$	19,356
Less: current portion	(5,928		)
Operating lease liabilities, non-current	$	13,428

Stock Compensation (Tables)

3 Months Ended

Mar. 31, 2019

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

Schedule of Other Share-based Compensation, Activity

A summary of restricted stock unit activity for the three months ended March 31, 2019 is as follows:



	Number of Shares Outstanding		Weighted- Average Grant Date Fair Value
Balance as of December 31, 2018	9,528,602		$	3.54
Restricted Stock Units granted	1,189,450		$	3.40
Restricted Stock Units vested	(967,712	)	$	3.89
Restricted Stock Units forfeited and canceled ⁽¹⁾	(655,982	)	$	3.54
Balance as of March 31, 2019	9,094,358		$	3.48

⁽¹⁾ Includes PSUs that were granted in the prior year, which were canceled because performance targets were not achieved.

Schedule of Share-based Compensation, Stock Options, Activity

A summary of stock option activity for the three months ended March 31, 2019 is as follows:



	Options Outstanding		Weighted- Average Exercise Price		Aggregate Intrinsic Value (in thousands)
Balance as of December 31, 2018	6,265,223		$	2.65	$	3,499
Stock option grants	200,000		$	3.22
Stock options exercised	(1,060,870	)	$	1.58
Stock options forfeited and canceled	(21,987	)	$	3.04
Balance as of March 31, 2019	5,382,366		$	2.88	$	8,811

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions

The fair value of each option grant was estimated on the date of grant using the Black-Scholes option-valuation model with the following assumptions and fair value per share:



	Three Months Ended March 31, 2019
	2019	2018
Volatility	57%	57%
Expected life (in years)	6.06	6.06
Risk-free interest rate	2.57%	2.72	%	-	2.74%
Dividend yield	—%	—%

Net Loss per Share (Tables)

3 Months Ended

Mar. 31, 2019

Earnings Per Share [Abstract]

Calculation of Basic and Diluted Earnings per Share

The following table presents the calculation of basic and diluted net loss per share for the Company’s common stock (in thousands, except per share data):



	Three Months Ended March 31,
	2019						2018
	Class A			Class B			Class A			Class B
Net loss	$	(2,741	)	$	(7,798	)	$	(5,646	)	$	(8,798	)
Weighted-average shares used to compute basic and diluted net loss per share	37,189			105,811			52,764			82,230
Basic and diluted net loss per share	$	(0.07	)	$	(0.07	)	$	(0.11	)	$	(0.11	)

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share

The following securities were excluded from the calculation of diluted net loss per share for common stock because their effect would have been anti-dilutive for the periods presented (in thousands):



	Three Months Ended March 31,
	2019	2018
Stock options and restricted stock units	14,477	20,601
Warrants	115	115
Total	14,592	20,716

Accounting Standards and Significant Accounting Policies - Concentrations of Risk and Significant Customers (Details) - Largest Channel Partner - Customer Concentration Risk	3 Months Ended
	Mar. 31, 2019
Total Revenue
Concentration Risk [Line Items]
Concentration risk, percentage	24.00%
Accounts Receivable
Concentration Risk [Line Items]
Concentration risk, percentage	23.00%

Accounting Standards and Significant Accounting Policies - Recently Adopted Accounting Pronouncements (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease ROU asset	$ 15,989
Operating lease liability	$ 19,356
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease ROU asset		$ 17,300
Operating lease liability		$ 20,700

Revenue, Deferred Revenue, Contract Balances and Performance Obligations - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Concentration Risk [Line Items]
Deferred revenue	$ 24.7		$ 21.2
Contract with customer, asset, net	1.2		$ 1.0
Contract with customer liability, revenue recognized	11.2	$ 15.9
Contract with customer, liability, cumulative catch-up adjustment to revenue, change in estimate of transaction price	$ 1.4	$ 0.0
Indirect Channel \| Customer Concentration Risk \| Sales Revenue, Net
Concentration Risk [Line Items]
Concentration risk, percentage	26.00%	10.00%

Revenue, Deferred Revenue, Contract Balances and Performance Obligations - Performance Obligations (Details) $ in Millions	Mar. 31, 2019 USD ($)
Revenue from Contract with Customer [Abstract]
Revenue, remaining performance obligation	$ 145.4
Revenue, remaining performance obligation, percent	70.00%
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, period	12 months

Deferred Costs (Details) - USD ($)	3 Months Ended
Deferred Costs (Details) - USD ($)	Mar. 31, 2019	Mar. 31, 2018
Deferred costs, capitalized prepaid, and other assets disclosure [Roll Forward]
Deferred commissions, beginning	$ 20,142,000
Deferred commissions, additions	1,416,000
Deferred commissions, expense recognized	(2,491,000)
Deferred commissions, ending	19,067,000
Deferred professional service costs, beginning	10,133,000
Deferred professional service costs, additions	508,000
Deferred professional service costs, expense recognized	(969,000)
Deferred professional service costs, ending	9,672,000
Total deferred commissions and professional service costs, beginning	30,275,000
Total deferred commissions and professional service costs, additions	1,924,000
Total deferred commissions and professionals service costs, expense recognized	(3,460,000)
Total deferred commissions and professional service costs, ending	28,739,000
Deferred costs, impairment charges	$ 0	$ 0

Goodwill and Intangible Assets - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Changes in goodwill	$ 0
Amortization expense	$ 900,000	$ 1,100,000

Goodwill and Intangible Assets - Schedule of Finite-Lived Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Finite-lived Intangible Assets [Roll Forward]
Gross	$ 23,900	$ 23,900
Accumulated Amortization	(8,567)	(7,691)
Net	$ 15,333	$ 16,209
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Useful Life	10 years	10 years
Finite-lived Intangible Assets [Roll Forward]
Gross	$ 10,900	$ 10,900
Accumulated Amortization	(2,180)	(1,908)
Net	$ 8,720	$ 8,992
Developed technology
Finite-Lived Intangible Assets [Line Items]
Useful Life	5 years	5 years
Finite-lived Intangible Assets [Roll Forward]
Gross	$ 10,600	$ 10,600
Accumulated Amortization	(4,240)	(3,710)
Net	$ 6,360	$ 6,890
Backlog
Finite-Lived Intangible Assets [Line Items]
Useful Life	3 years	3 years
Finite-lived Intangible Assets [Roll Forward]
Gross	$ 1,500	$ 1,500
Accumulated Amortization	(1,314)	(1,256)
Net	186	244
Other acquired intangible assets
Finite-lived Intangible Assets [Roll Forward]
Gross	900	900
Accumulated Amortization	(833)	(817)
Net	$ 67	$ 83
Other acquired intangible assets \| Minimum
Finite-Lived Intangible Assets [Line Items]
Useful Life	1 year	1 year
Other acquired intangible assets \| Maximum
Finite-Lived Intangible Assets [Line Items]
Useful Life	3 years	3 years

Goodwill and Intangible Assets - Schedule of Finite-Lived Intangible Assets, Future Amortization Expense (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Remainder of 2019	$ 2,629
2020	3,242
2021	3,210
2022	1,620
2023	1,090
Thereafter	3,542
Net	$ 15,333	$ 16,209

Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 27,467	$ 33,253
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	27,467	33,253
Included in cash and cash equivalents
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		21,926
Unrealized Gains		0
Unrealized Losses		0
Fair Value		21,926
Included in marketable securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		11,327
Unrealized Gains		0
Unrealized Losses		0
Fair Value		11,327
U.S. treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,138	7,980
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	3,138	7,980
U.S. agency obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	16,706	18,158
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	16,706	18,158
Money market mutual funds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,623	7,115
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	$ 7,623	$ 7,115

Fair Value Measurements - Summary of Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 27,467	$ 33,253
U.S. agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	16,706	18,158
U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	3,138	7,980
Money market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	7,623	7,115
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	27,467	33,253
Fair Value, Measurements, Recurring \| U.S. agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	16,706	14,811
Marketable securities		3,347
Fair Value, Measurements, Recurring \| U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	3,138
Marketable securities		7,980
Fair Value, Measurements, Recurring \| Money market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	7,623	7,115
Fair Value, Measurements, Recurring \| Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	7,623	7,115
Fair Value, Measurements, Recurring \| Level 1 \| U.S. agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Marketable securities		0
Fair Value, Measurements, Recurring \| Level 1 \| U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0
Marketable securities		0
Fair Value, Measurements, Recurring \| Level 1 \| Money market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	7,623	7,115
Fair Value, Measurements, Recurring \| Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	19,844	26,138
Fair Value, Measurements, Recurring \| Level 2 \| U.S. agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	16,706	14,811
Marketable securities		3,347
Fair Value, Measurements, Recurring \| Level 2 \| U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	3,138
Marketable securities		7,980
Fair Value, Measurements, Recurring \| Level 2 \| Money market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 0	$ 0

Fair Value Measurements - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
Fair Value Measurements - Narrative (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Debt securities, available-for-sale, realized gain (loss)	$ 0
Debt securities available-for-sale securities, maturity period	1 year	1 year

Property and Equipment - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property and equipment	$ 15,127	$ 15,002
Accumulated depreciation	(11,373)	(11,039)
Property and equipment, net	3,754	3,963
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment	3,102	3,102
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment	6,931	6,860
Software
Property, Plant and Equipment [Line Items]
Property and equipment	1,097	1,097
Internal-use software
Property, Plant and Equipment [Line Items]
Property and equipment	2,925	2,925
Furniture and equipment
Property, Plant and Equipment [Line Items]
Property and equipment	$ 1,072	$ 1,018

Property and Equipment - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 0.5	$ 0.7

Debt - Narrative (Details) - USD ($)	Apr. 03, 2017	Mar. 31, 2019
Line of Credit Facility [Line Items]
Long-term debt	$ 5,600,000	$ 4,648,000
Debt instrument, term	36 months
Early repayment of senior debt	$ 500,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Borrowings made		$ 0
Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 25,000,000
Interest Rate Option A
Line of Credit Facility [Line Items]
Spread on variable rate	1.00%
Interest Rate Option B
Line of Credit Facility [Line Items]
Debt instrument, interest rate, stated percentage	0.00%

Debt - Future Maturities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Apr. 03, 2017
Debt Disclosure [Abstract]
Remainder of 2019	$ 1,394
2020	1,859
2021	1,395
Total future maturities of debt	4,648		$ 5,600
Less current maturities	(1,859)
Debt, non-current	$ 2,789	$ 3,254
Early repayment of senior debt			$ 500

Leases - Information About Operating Leases (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Lease cost:
Operating lease cost	$ 1,649
Variable lease cost	151
Sublease income	(616)
Total lease cost	1,184
Other information:
Operating cash flows used in the measurement of operating lease liabilities	$ 1,749
Weighted-average remaining lease term - operating leases (in years)	3 years 186 days
Weighted-average discount rate - operating leases	7.45%

Leases - Maturities of Lease Liabilities (Details) $ in Thousands	Mar. 31, 2019 USD ($)
Leases [Abstract]
Remainder of 2019	$ 5,336
2020	6,524
2021	5,355
2022	3,050
2023	677
2024 and later	1,111
Total lease payments	22,053
Less: Interest	(2,697)
Present value of lease liabilities	19,356
Less: current portion	(5,928)
Operating lease liabilities, non-current	$ 13,428

Stock Compensation - Summary of Restricted Stock Unit Activity (Details) - Restricted Stock Units	3 Months Ended
	Mar. 31, 2019 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Balance as of beginning of period (in shares) \| shares	9,528,602
Restricted Stock Units granted (in shares) \| shares	1,189,450
Restricted Stock Units vested (in shares) \| shares	(967,712)
Restricted Stock Units forfeited and canceled (in shares) \| shares	(655,982)
Balance as of end of period (in shares) \| shares	9,094,358
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Balance as of beginning of period (in usd per share) \| $ / shares	$ 3.54
Restricted Stock Units granted (in usd per share) \| $ / shares	3.40
Restricted Stock Units vested (in usd per share) \| $ / shares	3.89
Restricted stock units forfeited and canceled (in usd per share) \| $ / shares	3.54
Balance as of end of period (in usd per share) \| $ / shares	$ 3.48

Stock Compensation - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock granted, value, share-based compensation, gross	$ 0.4	$ 0.3
Employee service share-based compensation, nonvested awards, compensation not yet recognized, stock options	1.2
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost	$ 29.1
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized, period for recognition	2 years 255 days
Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized, period for recognition	2 years 182 days

Stock Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Options Outstanding
Balance as of beginning of period (in shares)	6,265,223
Stock options grants (in shares)	200,000
Stock options exercised (in shares)	(1,060,870)
Stock options forfeited and canceled (in shares)	(21,987)
Balance as of end of period (in shares)	5,382,366
Weighted- Average Exercise Price
Balance as of beginning of period (in usd per share)	$ 2.65
Stock options grants (in usd per share)	3.22
Stock options exercised (in usd per share)	1.58
Stock options forfeited and canceled (in usd per share)	3.04
Balance as of end of period (in usd per share)	$ 2.88
Aggregate Intrinsic Value (in thousands)
Aggregate Intrinsic Value (in thousands)	$ 8,811	$ 3,499

Stock Compensation - Assumptions Related to Share-based Compensation (Details) - Stock Option	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Volatility	57.00%	57.00%
Expected life (in years)	6 years 22 days	6 years 22 days
Risk-free interest rate	2.57%
Dividend yield	0.00%	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate		2.72%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate		2.74%

Stockholders' Equity (Details)	Mar. 31, 2019 shares
Class A
Class of Stock [Line Items]
Common stock, shares, outstanding	36,137,783
Class B
Class of Stock [Line Items]
Common stock, shares, outstanding	107,818,004

Income Taxes (Details)	3 Months Ended
Income Taxes (Details)	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Effective income tax rate reconciliation, percent	0.00%

Net Loss per Share - Calculation of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Class of Stock [Line Items]
Net loss	$ (10,539)	$ (14,444)
Weighted-average shares used to compute basic and diluted net loss per share (in shares)	143,000	134,994
Basic and diluted net loss per share (in usd per share)	$ (0.07)	$ (0.11)
Class A
Class of Stock [Line Items]
Net loss	$ (2,741)	$ (5,646)
Weighted-average shares used to compute basic and diluted net loss per share (in shares)	37,189	52,764
Basic and diluted net loss per share (in usd per share)	$ (0.07)	$ (0.11)
Class B
Class of Stock [Line Items]
Net loss	$ (7,798)	$ (8,798)
Weighted-average shares used to compute basic and diluted net loss per share (in shares)	105,811	82,230
Basic and diluted net loss per share (in usd per share)	$ (0.07)	$ (0.11)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Net Loss per Share - Summary of Antidilutive Securities (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from the calculation of diluted net loss per share	14,592	20,716
Stock options and restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from the calculation of diluted net loss per share	14,477	20,601
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from the calculation of diluted net loss per share	115	115

Label	Element	Value
Restricted Cash	us-gaap_RestrictedCash	$ 1,325,000
Restricted Cash	us-gaap_RestrictedCash	$ 1,325,000