Cornerstone OnDemand (CSOD) 10-K 26 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2018	Feb. 20, 2019	Jun. 30, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Trading Symbol	CSOD
Entity Registrant Name	CORNERSTONE ONDEMAND INC
Entity Central Index Key	1,401,680
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		59,100,210
Entity Public Float			$ 1,303,889,877
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Assets
Cash and cash equivalents	$ 183,596	$ 393,576
Short-term investments	204,732	169,551
Accounts receivable, net	125,300	154,428
Deferred commissions, current portion	24,467	42,806
Prepaid expenses and other current assets	34,940	21,754
Total current assets	573,035	782,115
Capitalized software development costs, net	45,416	37,431
Deferred commissions, net of current portion	45,444	0
Property and equipment, net	77,254	20,817
Long-term investments	1,250	96,949
Intangible assets, net	13,867	0
Goodwill	47,453	25,894
Other assets, net	3,437	3,984
Total Assets	807,156	967,190
Liabilities:
Accounts payable	11,921	17,637
Accrued expenses	68,331	57,528
Deferred revenue, current portion	312,526	311,997
Convertible notes, net	0	248,025
Other liabilities	7,645	9,051
Total current liabilities	400,423	644,238
Convertible notes, net	288,967	285,168
Other liabilities, non-current	2,484	1,498
Deferred revenue, net of current portion	13,275	14,166
Facility financing obligation	46,100	0
Total liabilities	751,249	945,070
Commitments and contingencies (Note 16)
Stockholders’ Equity:
Common stock, $0.0001 par value; 1,000,000 shares authorized, 58,886 and 57,512 shares issued and outstanding at December 31, 2018 and 2017, respectively	6	6
Additional paid-in capital	585,387	536,951
Accumulated deficit	(529,962)	(515,054)
Accumulated other comprehensive income	476	217
Total stockholders’ equity	55,907	22,120
Total Liabilities and Stockholders’ Equity	$ 807,156	$ 967,190

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Common stock par value (usd per share)	$ 0.0001	$ 0.0001
Common stock authorized (in shares)	1,000,000,000	1,000,000,000
Common stock issued (in shares)	58,886,000	57,512,000
Common stock outstanding (in shares)	58,886,000	57,512,000

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Revenue	$ 537,891	$ 481,985	$ 423,124
Cost of revenue	144,349	142,867	135,752
Gross profit	393,542	339,118	287,372
Operating expenses:
Sales and marketing	224,635	240,271	225,781
Research and development	76,981	61,975	46,977
General and administrative	90,749	84,589	70,956
Restructuring	8,946	1,539	0
Total operating expenses	401,311	388,374	343,714
(Loss) income from operations	(7,769)	(49,256)	(56,342)
Other income (expense):
Interest income	7,796	2,951	1,702
Interest expense	(28,176)	(14,762)	(12,924)
Other, net	(3,098)	1,478	1,934
Other income (expense), net	(23,478)	(10,333)	(9,288)
Loss before income tax provision	(31,247)	(59,589)	(65,630)
Income tax provision	(2,595)	(1,746)	(1,207)
Net loss	$ (33,842)	$ (61,335)	$ (66,837)
Net loss per share — basic and diluted (usd per share)	$ (0.58)	$ (1.07)	$ (1.20)
Weighted average common shares outstanding, basic and diluted (in shares)	58,159	57,262	55,595

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net loss	$ (33,842)	$ (61,335)	$ (66,837)
Other comprehensive income, net of tax:
Foreign currency translation adjustment	(210)	(3,795)	3,748
Net change in unrealized gains (losses) on investments	469	(434)	88
Other comprehensive income (loss), net of tax	259	(4,229)	3,836
Total comprehensive loss	$ (33,583)	$ (65,564)	$ (63,001)

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital (Deficit)	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2015		54,704
Beginning balance at Dec. 31, 2015	$ 7,822	$ 5	$ 394,089	$ (386,882)	$ 610
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon the exercise of options (in shares)		978
Issuance of common stock upon the exercise of options	18,905	$ 1	18,904
Vesting of restricted stock units (in shares)		699
Shares issued under employee stock purchase plan (in shares)		135
Shares issued under employee stock purchase plan	4,286		4,286
Stock-based compensation	58,951		58,951
Net loss	(66,837)			(66,837)
Other comprehensive income (loss), net of tax	3,836				3,836
Ending balance (in shares) at Dec. 31, 2016		56,516
Ending balance at Dec. 31, 2016	26,963	$ 6	476,230	(453,719)	4,446
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon the exercise of options (in shares)		414
Issuance of common stock upon the exercise of options	6,777		6,777
Vesting of restricted stock units (in shares)		1,035
Shares issued under employee stock purchase plan (in shares)		182
Shares issued under employee stock purchase plan	$ 5,621		5,621
Repurchase of common stock (in shares)	(635)
Repurchase of common stock	$ (22,599)		(22,599)
Stock-based compensation	70,922		70,922
Net loss	(61,335)			(61,335)
Other comprehensive income (loss), net of tax	(4,229)				(4,229)
Ending balance (in shares) at Dec. 31, 2017		57,512
Ending balance at Dec. 31, 2017	$ 22,120	$ 6	536,951	(515,054)	217
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon the exercise of options (in shares)	1,472	1,474
Issuance of common stock upon the exercise of options	$ 47,816		47,816
Vesting of restricted stock units (in shares)		1,370
Shares issued under employee stock purchase plan (in shares)		181
Shares issued under employee stock purchase plan	$ 6,422		6,422
Repurchase of common stock (in shares)	(1,651)
Repurchase of common stock	$ (77,401)		(77,401)
Stock-based compensation	71,599		71,599
Net loss	(33,842)			(33,842)
Other comprehensive income (loss), net of tax	259				259
Ending balance (in shares) at Dec. 31, 2018		58,886
Ending balance at Dec. 31, 2018	$ 55,907	$ 6	$ 585,387	$ (529,962)	$ 476

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net loss	$ (33,842)	$ (61,335)	$ (66,837)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	35,260	35,377	32,392
Accretion of debt discount and amortization of debt issuance costs	8,929	9,833	9,130
Purchased investment premium, net of amortization	(160)	1,135	240
Net foreign currency gain	(440)	(2,461)	(7)
Stock-based compensation expense	66,557	65,924	54,699
Write-off of capitalized software	0	1,339	0
Deferred income taxes	(123)	52	(736)
Changes in operating assets and liabilities:
Accounts receivable	27,199	(14,317)	(38,092)
Deferred commissions	(15,316)	(5,249)	(2,543)
Prepaid expenses and other assets	(11,443)	(2,704)	(3,623)
Accounts payable	(5,496)	(6,820)	5,939
Accrued expenses	9,291	8,530	3,727
Deferred revenue	10,803	35,829	43,379
Other liabilities	(1,212)	2,377	(2,416)
Net cash provided by operating activities	90,253	67,510	35,252
Cash flows from investing activities:
Purchases of investments	(125,109)	(323,413)	(210,534)
Maturities of investments	185,733	314,418	151,533
Capital expenditures	(14,895)	(7,100)	(6,228)
Capitalized software costs	(25,515)	(20,571)	(16,409)
Cash paid for acquisition, net of cash acquired	(41,090)	0	0
Net cash used in investing activities	(20,876)	(36,666)	(81,638)
Cash flows from financing activities:
Payments of debt issuance costs and proceeds from convertible notes	(152)
Payments of debt issuance costs and proceeds from convertible notes		285,077	0
Repayment of debt	(253,000)	0	0
Principal payments under capital lease obligations	0	0	(33)
Proceeds from employee stock plans	54,402	12,509	23,548
Repurchases of common stock	(79,266)	(20,734)	0
Net cash (used in) provided by financing activities	(278,016)	276,852	23,515
Effect of exchange rate changes on cash and cash equivalents	(1,341)	2,580	(1,520)
Net (decrease) increase in cash and cash equivalents	(209,980)	310,276	(24,391)
Cash and cash equivalents at beginning of period	393,576	83,300	107,691
Cash and cash equivalents at end of period	183,596	393,576	83,300
Supplemental cash flow information:
Cash paid for interest	13,628	3,841	3,796
Cash paid for income taxes	1,859	2,243	2,334
Proceeds from employee stock plans received in advance of stock issuance	642	575	489
Non-cash investing and financing activities:
Assets acquired under capital leases and other financing arrangements	47,070	3,467	0
Capitalized assets financed by accounts payable and accrued expenses	1,566	1,829	2,080
Capitalized stock-based compensation	5,042	4,998	4,252
Deferred debt issuance costs included in accrued expenses	0	152	0
Unsettled share repurchase in other liabilities	$ 0	$ 1,866	$ 0

Organization

Organization	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	ORGANIZATION Company Overview Cornerstone OnDemand, Inc. (“Cornerstone” or the “Company”) was incorporated on May 24, 1999 in the state of Delaware and began its principal operations in November 1999 . The Company is a leading global provider of learning and human capital management software, delivered as Software-as-a-Service (“SaaS”). The Company helps organizations around the globe recruit, train and manage their employees. It is one of the world’s largest cloud computing companies. The Company's human capital management platform combines the world’s leading unified talent management solutions with state-of-the-art analytics and HR administration solutions to enable organizations to manage the entire employee lifecycle. Its focus on continuous learning and development helps organizations to empower employees to realize their potential and drive success. The Company works with clients across all geographies, verticals and market segments. Its Recruiting, Learning, Performance and HR Administration suites help with sourcing, recruiting and onboarding new hires; managing training and development requirements; nurturing knowledge sharing and collaboration among employees; goal setting reviews, competency management and continuous feedback; linking compensation to performance; identifying development plans based on performance gaps; streamlining employee data management, self-service and compliance reporting; and then utilizing state-of-the-art analytics capabilities to make smarter, more-informed decisions using data from across the platform for talent mobility, engagement and development so that HR and leadership can focus on strategic initiatives to help their organization succeed. The Company’s management has determined that the Company operates in one segment as it only reports financial information on an aggregate and consolidated basis to the Company’s chief executive officer, who is the Company’s chief operating decision maker.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation and Principles of Consolidation The accompanying consolidated financial statements are presented in accordance with accounting standards generally accepted in the United States of America (“GAAP”), and include the accounts of Cornerstone OnDemand, Inc. and its wholly owned subsidiaries. All significant inter-company transactions and balances have been eliminated in consolidation. Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Actual results could differ from those estimates. On an on-going basis, management evaluates its estimates, including among others those related to: (i) the realization of tax assets and estimates of tax liabilities and reserves, (ii) the recognition and disclosure of contingent liabilities, (iii) the evaluation of revenue recognition criteria, including the determination of standalone value and estimates of the selling price of multiple-deliverables in the Company’s revenue arrangements, (iv) fair values of investments in marketable securities and strategic investments carried at fair value, (v) the fair values of acquired assets and assumed liabilities in business combinations, (vi) the useful lives of property and equipment, capitalized software and intangible assets, (vii) impairment of long-lived assets, (viii) the period of amortization of the commission payments to record to expense and (ix) determination of the number of shares that are probable of vesting for performance-based restricted stock unit awards. These estimates are based on historical data and experience, as well as various other factors that management believes to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying value of assets and liabilities that are not readily apparent from other sources. The Company engages third-party valuation specialists to assist with the allocation of the purchase price in business combinations. Such estimates required the selection of appropriate valuation methodologies and models and significant judgment in evaluating ranges of assumptions and financial inputs. Business Combinations The results of businesses acquired in a business combination are included in the Company’s consolidated financial statements from the date of the acquisition. Purchase accounting results in assets and liabilities of an acquired business being recorded at their estimated fair values on the acquisition date. Any excess consideration over the fair value of assets acquired and liabilities assumed is recognized as goodwill. The Company performs valuations of assets acquired and liabilities assumed for an acquisition and allocates the purchase price to its respective net tangible and intangible assets. The Company engages the assistance of valuation specialists in concluding on fair value measurements in connection with determining fair values of assets acquired and liabilities assumed in a business combination. Revenue Recognition Effective January 1, 2018, the Company adopted the guidance under Topic 606 on a modified retrospective approach. All balances reported prior to this date are presented under Topic 605. Refer to the discussion under Recently Adopted Accounting Pronouncements below to understand the impacts of adopting Topic 606 on our financial statements. The Company derives its revenue from the following sources: Subscriptions to the Company’s products and other offerings on a recurring basis Clients pay subscription fees for access to the Company’s enterprise human capital management platform, other products and support on a recurring basis. Fees are based on a number of factors, including the number of products purchased, which may include e-learning content, and the number of users having access to a product. The Company generally recognizes revenue from subscriptions ratably over the term of the agreements beginning on the date the subscription service is made available to the client. Subscription agreements are typically three years, billed annually in advance, and non-cancelable, with payment due within 30 days of the invoice date. Professional services and other The Company offers its clients and implementation partners assistance in implementing its products and optimizing their use. Professional services include application configuration, system integration, business process re-engineering, change management and training services. Services are generally billed up-front on a fixed fee basis and to a lesser degree on a time-and-material basis. These services are generally purchased as part of a subscription arrangement and are typically performed within the first several months of the arrangement. Clients may also purchase professional services at any other time. The Company generally recognizes revenue from fixed fee professional services contracts as services are performed based on the proportion performed to date relative to the total expected services to be performed. Revenue associated with time-and-material contracts are recorded as such time-and-materials are incurred. The Company recognizes revenue from contracts with customers based on the following five steps: 1) Identification of the contract, or contracts, with a customer 2) Identification of all performance obligations in the contract 3) Determination of the transaction price 4) Allocation of the transaction price to the performance obligations in the contract 5) Recognition of revenue as the Company satisfies a performance obligation The Company identifies enforceable contracts with a customer when the agreement is signed. The Company accounts for individual performance obligations separately if they are distinct. The transaction price is generally based on fixed fees stated in the contract. The Company excludes from the transaction price any amounts relating to taxes from product sales which are collected from customers and remitted to governmental authorities. If the contract contains a single performance obligation, the entire transaction price is allocated to the single performance obligation. Contracts that contain multiple performance obligations require an allocation of the transaction price to each performance obligation based on a relative standalone selling price basis. The Company is not able to directly observe a standalone selling price for its performance obligations, as the performance obligations are sold separately and within a sufficiently narrow price range only infrequently, and because management has determined that there are no third-party offerings reasonably comparable to the Company’s products. Accordingly, total contract values are allocated to subscriptions to the products and professional services based on the standalone selling price (“SSP”). The determination of SSP requires the Company to make certain estimates and judgments. The Company considers numerous factors, including the nature and complexity of the performance obligations themselves; the geography, market conditions and competitive landscape for the sale; internal costs; and pricing and discounting practices. The Company updates its estimates of SSP on an ongoing basis through internal periodic reviews and as events or circumstances may require. Revenue is recognized at the time the related performance obligation is satisfied by transferring a promised service to a customer. The Company satisfies performance obligations over time. In a limited number of cases, the client’s intended use of a product requires contractually specified enhancements to its underlying features and functionality. In some of these cases, revenue is recognized as a combined single performance obligation on a straight-line basis from the point at which access to the enhanced product(s) have been provided, through the remaining term of the agreement. In other cases where the enhancement is not contractually specified by the customer for its initial use, revenue is recognized separately for the enhancement and the product as a second distinct performance obligation. In such cases where a second performance obligation exists, the enhancement revenue is recognized based on a SSP allocation on a straight-line basis once access to the enhancement has been provided, through the remaining term of the agreement. For arrangements in which the Company resells third-party e-learning training content to clients, revenue is recognized in accordance with accounting guidance as to when to report gross revenue as a principal or report net revenue as an agent. The Company typically recognizes third-party content revenue at the gross amount invoiced to clients as (i) the Company is primarily responsible for hosting the content on the Company's platform for the term of the agreement, (ii) the Company controls the content before access is provided to the customer, and (iii) the Company typically has discretion to establish the price charged. Deferred Revenue The Company records amounts that have been invoiced to its clients in accounts receivable and in either deferred revenue or revenue depending on whether the revenue recognition criteria described above have been met. Deferred revenue that will be recognized during the succeeding twelve-month period from the respective balance sheet date is recorded as current deferred revenue and the remaining portion is recorded as noncurrent. The decrease in the deferred revenue balance for the year ended December 31, 2018 is primarily driven by $301.6 million of revenue recognized that were included in the deferred revenue balances as of January 1, 2018 offset by invoices billed in advance of satisfying performance obligations in accordance with contract payment terms. Transaction Price Allocated to Remaining Performance Obligations As of December 31, 2018 , approximately $876.0 million of revenue is expected to be recognized from remaining performance obligations. This amount mainly comprises subscription revenue, with less than 10% attributable to professional services and other revenue. The Company expects to recognize revenue on approximately two thirds of these remaining performance obligations over the next 18 months , with the balance recognized thereafter. The estimated revenues from the remaining performance obligations do not include uncommitted contract amounts such as (i) amounts which are cancelable by the client without any significant penalty, (ii) future billings for time-and-material contracts, and (iii) amounts associated with optional renewal periods. Sales Commission The Company defers commissions paid to its sales force and related payroll taxes as these amounts are incremental costs of obtaining a contract with a customer and are recoverable from future revenue due to the non-cancelable client agreements that gave rise to the commissions. Commissions for initial contracts are deferred on the consolidated balance sheets and amortized on a straight-line basis over a period of benefit that has been determined to be six years. The Company took into consideration technology and other factors in estimating the benefit period. Sales commissions for renewal contracts are deferred and amortized on a straight-line basis over the related contract renewal period. Amortization expense is included in sales and marketing expenses in the accompanying consolidated statements of operations. The Company generally commences payment of commissions within 45 to 75 days after execution of client agreements. During the years ended December 31, 2018 , 2017 and 2016 , the Company deferred $65.3 million , $48.2 million and $33.3 million , respectively, of commissions on the consolidated balance sheets. During the years ended December 31, 2018 , 2017 and 2016 , the Company recognized $37.9 million , $41.7 million and $33.0 million in commissions expense to sales and marketing expense, respectively. As of December 31, 2018 and 2017 , deferred commissions on the Company’s consolidated balance sheets totaled $69.9 million and $42.8 million , respectively. Impact of New Standard on Financial Statement Line Items The following tables summarize the effect of the adoption of Topic 606 on the Company’s select line items, included in the consolidated condensed financial statements as of and for the year ended December 31, 2018 , as if the previous accounting was in effect (in thousands). December 31, 2018 Consolidated Condensed Balance Sheet As Reported Impacts of Adoption Without Adoption Assets Deferred commissions, current portion $ 24,467 $ 30,624 $ 55,091 Deferred commissions, non-current 45,444 (45,444 ) — Liabilities Accrued expenses 68,331 (1,697 ) 66,634 Deferred revenue, current portion 312,526 6,751 319,277 Stockholders’ Equity Accumulated deficit (529,962 ) (19,874 ) (549,836 ) Year Ended December 31, 2018 Consolidated Condensed Statement of Operations As Reported Impacts of Adoption Without Adoption Revenue $ 537,891 $ (696 ) $ 537,195 Operating expenses: Sales and marketing 224,635 (992 ) 223,643 Net loss (33,842 ) 296 (33,546 ) Net loss per share, basic and diluted (0.58 ) (0.58 ) Weighted average common shares outstanding, basic and diluted 58,159 58,159 The adoption of Topic 606 had no impact to net cash provided by or used in operating, investing or financing activities in the Company’s consolidated statements of cash flows for the year ended December 31, 2018. Cost of Revenue Cost of revenue consists primarily of costs related to hosting our products and delivery of professional services, and includes the following: • personnel and related expenses, including stock-based compensation; • expenses for network-related infrastructure and IT support; • delivery of contracted professional services and on-going client support staff; • payments to external service providers contracted to perform implementation services; • depreciation of data centers and amortization of capitalized software costs, developed technology software license rights, content and licensing fees and referral fees. In addition, the Company allocates a portion of overhead, such as rent, IT costs, depreciation and amortization and employee benefits costs, to cost of revenue based on headcount. Costs associated with providing professional services are recognized as incurred when the services are performed. Out-of-pocket travel costs related to the delivery of professional services are typically reimbursed by the client and are accounted for as both revenue and cost of revenue in the period in which the cost is incurred. Research and Development Research and development expenses consist primarily of personnel and related expenses for the Company’s research and development staff, including salaries, benefits, bonuses and stock-based compensation; the cost of certain third-party service providers; and allocated overhead. Research and development expenses, other than software development costs qualifying for capitalization, are expensed as incurred. Advertising Advertising expenses for 2018 , 2017 and 2016 were $7.1 million , $9.0 million and $6.6 million , respectively, and are expensed as incurred and is recorded within Sales and Marketing in the accompanying consolidated statements of operations. Stock-Based Compensation The Company accounts for stock-based awards granted to employees and directors by recording compensation expense based on the awards’ estimated fair values. The Company grants stock options and restricted stock units that vest over time based on the continuing employment of the employee, as well as restricted stock units that vest based on meeting certain performance targets. The Company estimates the fair value of its restricted stock units based on the closing price of its common stock as of the date of grant. The Company estimates the fair value of its stock options as of the date of grant using the Black-Scholes option-pricing model. Determining the fair value of stock options under this model requires judgment, including estimating (i) the value per share of the Company's common stock, (ii) volatility, (iii) the term of the awards, (iv) the dividend yield and (v) the risk-free interest rate. The assumptions used in calculating the fair value of stock based awards represent the Company’s best estimates, based on management’s judgment and subjective future expectations. These estimates involve inherent uncertainties. If any of the assumptions used in the model change significantly, stock-based compensation recorded for future awards may differ materially from that recorded for awards granted previously. Beginning in 2017, the Company began estimating expected volatility based solely on its historical volatility as a public company. In previous years, the Company estimated this using the average volatility of similar publicly traded companies as sufficient trading history of the Company’s stock was not available. For purposes of determining the expected term of the awards in the absence of sufficient historical data relating to stock option exercises for the Company, it applies a simplified approach in which the expected term of an award is presumed to be the mid-point between the vesting date and the expiration date of the award. The risk-free interest rate for periods within the expected life of an award, as applicable, is based on the United States Treasury yield curve in effect during the period the award was granted. The estimated dividend yield is zero, as the Company has not declared dividends in the past and does not currently intend to declare dividends in the foreseeable future. The following information represents the weighted average of the assumptions used in the Black-Scholes option-pricing model for stock options granted during each of the last three years: For the Years Ended December 31, 2018 2017 2016 Risk-free interest rate n/a n/a 1.4 % Expected term (in years) n/a n/a 5.8 Estimated dividend yield n/a n/a — % Estimated volatility n/a n/a 48.8 % Once the Company has determined the estimated fair value of its stock-based awards, it recognizes the portion of that value that corresponds to the portion of the award that is ultimately expected to vest, taking estimated forfeitures into account. This amount is recognized as an expense over the vesting period of the award using the straight-line method for awards which contain only service conditions, and using the graded vesting method based upon the probability of the performance condition being met for awards which contain performance conditions. The Company estimates forfeitures based upon its historical experience and for each period, the Company reviews the estimated forfeiture rate and makes changes as factors affecting the forfeiture rate calculations and assumptions change. In addition, the Company has issued performance-based restricted stock units that vest based upon continued service over the vesting term and achievement of certain performance goals, established by the Board of Directors, for a predetermined period. The fair value of the performance-based awards are determined based upon the closing price of the Company’s common stock on the date of the grant and the Company recognizes the fair value of awards only if it is probable the performance condition will be met. For performance-based awards, the fair value is not determined until all of the terms and conditions of the award are established. Due to the full valuation allowance provided on its net deferred tax assets, the Company has not recorded any significant tax benefit attributable to stock-based compensation expense as of December 31, 2018 , 2017 and 2016. Capitalized Software Costs The Company capitalizes the costs associated with software developed or obtained for internal use, including costs incurred in connection with the development of its products, when the preliminary project stage is completed, management has decided to make the project a part of its future offering and the software will be used to perform the function intended. These capitalized costs include external direct costs of materials and services consumed in developing or obtaining internal-use software, personnel and related expenses for employees who are directly associated with and who devote time to internal-use software projects and, when material, interest costs incurred during the development. Capitalization of these costs ceases once the project is substantially complete and the software is ready for its intended purpose. Costs incurred for upgrades and enhancements to the products are also capitalized. Post-configuration training and maintenance costs are expensed as incurred. Capitalized software costs are amortized to cost of revenue using the straight-line method over an estimated useful life of the software, which is typically three years , commencing when the software is ready for its intended use. The Company does not transfer ownership of or lease its software to its clients. During the years ended December 31, 2018 , 2017 and 2016 , the Company capitalized $31.6 million , $24.3 million and $20.9 million , respectively, of software development costs to the consolidated balance sheets. During the years ended December 31, 2018 , 2017 and 2016 , the Company amortized $23.5 million , $17.6 million and $13.2 million to cost of revenue, respectively. Based on the Company’s capitalized software costs at December 31, 2018 , estimated amortization expense of $22.3 million , $13.5 million , $4.6 million and $0.1 million is expected to be recognized in 2019 , 2020 , 2021 and 2022 , respectively. Comprehensive Loss Comprehensive loss encompasses all changes in equity other than those arising from transactions with stockholders, and consists of net loss, currency translation adjustments and unrealized gains or losses on investments. For the years ended December 31, 2018 , 2017 and 2016 , accumulated other comprehensive income (loss) comprised a cumulative translation adjustment and also included net unrealized gains (losses) on investments. Income Taxes The Company uses the liability method of accounting for income taxes. Under the liability method, deferred taxes are determined based on the temporary differences between the financial statement and tax bases of assets and liabilities, using tax rates expected to be in effect during the years in which the bases differences are expected to reverse. A valuation allowance is recorded when it is more likely than not that some of the deferred tax assets will not be realized. In determining the need for valuation allowances, the Company considers projected future taxable income and future reversals of existing taxable differences. The Company has recorded a full valuation allowance to reduce its United States, United Kingdom, New Zealand, Hong Kong and Brazil net deferred tax assets to zero, as it has determined that it is not more likely than not that any of these net deferred tax assets will be realized. The Company has assessed its income tax positions and recorded tax benefits for all years subject to examination, based upon its evaluation of the facts, circumstances and information available at each period end. For those tax positions where the Company has determined there is a greater than 50% likelihood that a tax benefit will be sustained, the Company has recorded the largest amount of tax benefit that may potentially be realized upon ultimate settlement with a taxing authority that has full knowledge of all relevant information. For those income tax positions where it is determined there is less than 50% likelihood that a tax benefit will be sustained, no tax benefit has been recognized. Cash and Cash Equivalents The Company considers cash and cash equivalents to include short-term, highly liquid investments that are readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value, including investments with original or remaining maturities from the date of purchase of three months or less. At December 31, 2018 and 2017 , cash and cash equivalents consisted of cash balances of $54.4 million and $24.7 million , respectively, money market funds backed by U.S. treasury securities of $129.2 million and $358.9 million , respectively, and certificates of deposit of $0.0 million and $10.0 million , respectively. Investments in Marketable Securities During the year ended December 31, 2018 the Company prospectively adopted ASU 2016-01, which requires equity securities to be measured at fair value and recognize any changes in fair value within the consolidated statements of operations. The adoption of this standard did not have a material impact on the Company’s consolidated financial statements. The cost of marketable securities sold is determined based on the specific identification method and any realized gains or losses on the sale of investments are reflected as a component of interest income or expense. In addition, the Company classifies marketable securities as current or non-current based upon the maturity dates of the securities. At December 31, 2018 and 2017 , the Company had $204.7 million and $263.5 million , respectively, of investments in marketable securities. Strategic Investments The Company has invested in equity securities of multiple privately-held companies. The Company accounted for each of these investment using the cost method of accounting, as the Company does not have significant influence or a controlling financial interest over these entities. These investments are subject to periodic impairment reviews and are considered to be impaired when a decline in fair value is judged to be other-than-temporary. These investments are included in long-term investments on the consolidated balance sheets, and any impairment losses are recorded in other, net in the accompanying consolidated statements of operations. Allowance for Doubtful Accounts The Company bases its allowance for doubtful accounts on its historical collection experience and a review in each period of the status of the then-outstanding accounts receivable. A reconciliation of the beginning and ending amount of allowance for doubtful accounts for the years ended December 31, 2018 , 2017 and 2016 , is as follows (in thousands): 2018 2017 2016 Beginning balance, January 1 $ 7,478 $ 3,532 $ 2,578 Additions and adjustments 1,691 7,680 3,165 Write-offs (6,740 ) (3,734 ) (2,211 ) Ending balance, December 31 $ 2,429 $ 7,478 $ 3,532 The Company recognized bad debt expense of $0.8 million , $1.4 million and $0.8 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. Property and Equipment, Net Property and equipment are recorded at historical cost, less accumulated depreciation and amortization. Depreciation is computed using the straight-line method based upon the estimated useful lives of the assets, generally two to seven years (See Note 7 ). Leasehold improvements are depreciated on a straight-line basis over the shorter of their estimated useful lives or lease terms. Repair and maintenance costs are charged to expense as incurred, while renewals and improvements are capitalized. Impairment of Long Lived Assets The Company evaluates the recoverability of its long-lived assets with finite useful lives, including intangible assets, for impairment whenever events or changes in circumstances indicate that the carrying amounts may not be recoverable. Such triggering events or changes in circumstances may include: a significant decrease in the market price of a long-lived asset, a significant adverse change in the extent or manner in which a long-lived asset is being used, a significant adverse change in legal factors or in the business climate, the impact of competition or other factors that could affect the value of a long-lived asset, a significant adverse deterioration in the amount of revenue or cash flows expected to be generated from an asset group, an accumulation of costs significantly in excess of the amount originally expected for the acquisition or development of a long-lived asset, current or future operating or cash flow losses that demonstrate continuing losses associated with the use of a long-lived asset, or a current expectation that, more likely than not, a long-lived asset will be sold or otherwise disposed of significantly before the end of its previously estimated useful life. The Company performs impairment testing at the asset group level that represents the lowest level for which identifiable cash flows are largely independent of the cash flows of other assets and liabilities. If events or changes in circumstances indicate that the carrying amount of an asset group may not be recoverable and the expected undiscounted future cash flows attributable to the asset group are less than the carrying amount of the asset group, an impairment loss equal to the excess of the asset’s carrying value over its fair value is recorded. Fair value is determined based upon estimated undiscounted future cash flows. There were no impairment charges related to identifiable long lived assets in the year ended December 31, 2018 . During the year ended December 31, 2017 , the Company determined that previously capitalized software costs were impaired resulting in the write-off of $1.3 million , which was recorded in research and development expense in the accompanying consolidated statements of operations. Intangible Assets Identifiable intangible assets primarily consist of acquisition-related intangibles. The Company determines the appropriate useful life of its intangible assets by performing an analysis of expected cash flows of the acquired assets. Intangible assets are amortized over their estimated useful lives ranging from three to six years, generally using the straight-line method which approximates the pattern in which the economic benefits are consumed. Goodwill Goodwill is not amortized, but instead is required to be tested for impairment annually and under certain circumstances. The Company performs such testing of goodwill in the fourth quarter of each year, or as events occur or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying amount. Events or changes in circumstances which could trigger an impairment review include a significant adverse change in legal factors or in the business climate, an adverse action or assessment by a regulator, unanticipated competition, a loss of key personnel, significant changes in the manner of the Company’s use of the acquired assets or the strategy for the Company’s overall business, significant negative industry or economic trends, or significant underperformance relative to expected historical or projected future results of operations. As part of the annual impairment test, the Company may conduct an assessment of qualitative factors to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount. Based on the results of the qualitative assessment, no impairment of goodwill existed at December 31, 2018 or 2017 . Convertible Notes In June 2013, the Company issued 1.50% convertible notes due July 1, 2018 with a principal amount of $253.0 million (the “2018 Notes”). In December 2017, the Company issued 5.75% senior convertible notes due July 1, 2021 with a principal amount of $300.0 million (the “2021 Notes”). In accounting for the 2018 Notes at issuance, the Company separated the 2018 Notes into debt and equity components pursuant to the accounting standards for convertible debt instruments that may be fully or partially settled in cash upon conversion. The fair value of the debt component was estimated using an interest rate, with terms similar to the 2018 Notes, excluding the conversion feature. The carrying amount of the liability component was calculated by measuring the fair value of similar liabilities that do not have an associated convertible feature. The excess of the principal amount of the 2018 Notes over the fair value of the debt component was recorded as a debt discount and a corresponding increase in additional paid-in capital. The debt discount is accreted to interest expense over the term of the 2018 Notes using the interest method. The equity component of the 2018 Notes recorded to additional paid-in capital is not to be remeasur

Business Acquisitions

Business Acquisitions	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Business Acquisitions	BUSINESS ACQUISITIONS Workpop Inc. On September 10, 2018, the Company completed the acquisition of Workpop Inc. (“Workpop”), a privately held company. Workpop is a robust web and mobile solution for candidates and hiring managers in service-based industries. The acquisition was completed pursuant to a merger whereby Workpop became a wholly-owned subsidiary of the Company. In connection with the merger, the Company paid cash consideration of approximately $18.2 million . The Company acquired Workpop to leverage and develop new web and mobile recruiting products as part of the Cornerstone Recruiting suite. The Company had a $0.5 million cost basis investment in Workpop prior to the acquisition. As part of the acquisition of Workpop, the Company received a return of its investment with an immaterial loss, which is included in general and administrative expenses in the consolidated statements of operations. The acquisition has been accounted for under the acquisition method of accounting for business combinations with the Company as the accounting acquirer in accordance with ASC 805, Business Combinations . As such, the Workpop assets acquired and liabilities assumed are recorded at their acquisition-date fair values. Acquisition-related transaction costs of $0.5 million are not included as a component of consideration transferred, but are accounted for as an expense in the period in which the costs are incurred. Accordingly, these acquisition-related transaction costs have been included in general and administrative expenses in the consolidated statements of operations. Any excess of the acquisition consideration over the fair value of assets acquired and liabilities assumed is allocated to goodwill. Goodwill is attributable primarily to expected benefits, including the acquired workforce, from combining Workpop with the Company. Upon the filing of the Company's 2018 tax returns, it expects all of the acquired goodwill to be deductible for tax purposes. The Company’s allocation of the total purchase price consideration as of September 10, 2018 is summarized below (in thousands): Fair Value Cash and cash equivalents $ 115 Other assets 68 Intangible assets - developed technology 7,500 Goodwill 10,525 Total purchase price $ 18,208 The fair value of the developed technology is being amortized on a straight-line basis over 3 years , which is the expected useful life of the asset. Pro forma results of operations have not been presented because the effects of this acquisition is not material to the Company's financial results. Grovo Learning, Inc. On November 9, 2018, the Company completed the acquisition of Grovo Learning, Inc. (“Grovo”), a privately held company. Grovo helps learning and development teams engage employees and drive their business forward by delivering an evolving library of customizable Microlearning® content. The acquisition was completed pursuant to a merger whereby Grovo became a wholly-owned subsidiary of the Company. In connection with the merger, the Company paid cash consideration of approximately $22.9 million . The Company acquired Grovo to expand its Cornerstone Content Anytime subscription offerings which are accessed through the Cornerstone Learning suite. The acquisition has been accounted for under the acquisition method of accounting for business combinations with the Company as the accounting acquirer in accordance with ASC 805, Business Combinations . As such, the Grovo assets acquired and liabilities assumed are recorded at their acquisition-date fair values. Acquisition-related transaction costs of $0.6 million are not included as a component of consideration transferred, but are accounted for as an expense in the period in which the costs are incurred. Accordingly, these acquisition-related transaction costs have been included in general and administrative expenses in the consolidated statements of operations. Any excess of the acquisition consideration over the fair value of assets acquired and liabilities assumed is allocated to goodwill. Goodwill is attributable primarily to expected benefits, including the acquired workforce, from combining Grovo with the Company. Upon the filing of the Company's 2018 tax returns, it expects all of the acquired goodwill to be deductible for tax purposes. The Company’s allocation of the total purchase price consideration as of November 9, 2018 is summarized below (in thousands): Fair Value Cash and cash equivalents 508 Accounts receivable 761 Property and equipment, net 51,967 Other current and noncurrent assets 1,001 Intangible assets - content library 4,700 Intangible assets - developed technology 2,500 Goodwill 11,034 Facility financing obligation (46,100 ) Accounts payable, accrued expenses, and other liabilities, current and noncurrent (3,465 ) Net assets acquired 22,906 The Company acquired a property lease and related leasehold improvements whereby it was deemed, for accounting purposes only, to be the owner of the entire project. In connection with the Company’s accounting for this transaction, the Company capitalized $51.1 million as a build-to-suit property within property and equipment, net, and recognized a corresponding facility financing lease obligation for approximately $46.1 million . Expected future lease payments under the build-to-suit lease as of December 31, 2018 are included in Note 16 - Commitments and Contingencies . The fair value of the building asset is being amortized on a straight-line basis over 25 years , which is the expected useful life of the asset. The fair value of the content library is being amortized on a straight-line basis over 6 years, which is the expected useful life of the asset. The fair value of the developed technology is being amortized on a straight-line basis over 3 years , which is the expected useful life of the asset. Pro forma results of operations have not been presented because the effects of this acquisition is not material to the Company's financial results.

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Net Loss Per Share	NET LOSS PER SHARE The following table presents the Company's basic and diluted net loss per share (in thousands, except per share amounts): For the Years Ended December 31, 2018 * 2017 2016 Net loss $ (33,842 ) $ (61,335 ) $ (66,837 ) Weighted-average shares of common stock outstanding 58,159 57,262 55,595 Net loss per share — basic and diluted $ (0.58 ) $ (1.07 ) $ (1.20 ) * See Note 2 for summary of adjustments in relation to the adoption of ASC 606. The potential shares of common stock that would have a dilutive impact are computed using the treasury stock method or the if-converted method, as applicable. At December 31, 2018 , 2017 and 2016 , the following potential shares were excluded from the computation of diluted net loss per share because their effect would have been anti-dilutive (in thousands): December 31, 2018 2017 2016 Options to purchase common stock, restricted stock units and performance-based restricted stock units 9,869 10,143 10,635 Shares issuable pursuant to employee stock purchase plan 97 114 89 Convertible notes 7,143 11,825 4,682 Common stock warrants 936 4,682 4,682 Total shares excluded from net loss per share 18,045 26,764 20,088

Investments

Investments	12 Months Ended
	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Investments	INVESTMENTS Investments in Marketable Securities The Company’s investments in available-for-sale marketable securities are made pursuant to its investment policy, which has established guidelines relative to the diversification of the Company’s investments and their maturities, with the principal objective of capital preservation and maintaining liquidity that is sufficient to meet cash flow requirements. The following is a summary of investments in marketable securities, including those that meet the definition of a cash equivalent, as of December 31, 2018 (in thousands): December 31, 2018 Amortized Cost Basis Unrealized Gains Unrealized Losses Fair Value Cash Equivalent Investments Money market funds $ 129,321 $ — $ — $ 129,321 $ 129,321 $ — Corporate bonds 58,115 — (82 ) 58,033 — 58,033 U.S. treasury securities 138,826 — (100 ) 138,726 — 138,726 Commercial paper $ 7,973 $ — $ — $ 7,973 $ — $ 7,973 $ 334,235 $ — $ (182 ) $ 334,053 $ 129,321 $ 204,732 The following is a summary of investments in marketable securities, including those that meet the definition of a cash equivalent, as of December 31, 2017 (in thousands): December 31, 2017 Amortized Cost Basis Unrealized Gains Unrealized Losses Fair Value Cash Equivalent Investments Money market funds $ 358,859 $ — $ — $ 358,859 $ 358,859 $ — Certificate of deposits 10,000 — — 10,000 10,000 — Corporate bonds 74,868 — (220 ) 74,648 — 74,648 U.S. treasury securities 189,310 — (430 ) 188,880 — 188,880 $ 633,037 $ — $ (650 ) $ 632,387 $ 368,859 $ 263,528 As of December 31, 2018 , the Company’s investment in corporate bonds and U.S. treasury securities had a weighted-average maturity date of approximately two months . Unrealized gains and losses on investments were not significant individually or in aggregate, and the Company does not believe the unrealized losses represent other-than-temporary impairments as of December 31, 2018 .

Intangible Assets and Goodwill

Intangible Assets and Goodwill	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets and Goodwill	INTANGIBLE ASSETS AND GOODWILL Finite-lived Intangibles The Company has finite-lived intangible assets, which are amortized over their estimated useful lives on a straight-line basis. The following table presents the gross carrying amount and accumulated amortization of finite-lived intangible assets as of December 31, 2018 and 2017 (in thousands): December 31, 2018 December 31, 2017 Gross Accumulated Net Gross Accumulated Net Developed technology $ 39,984 $ (30,817 ) $ 9,167 $ 29,984 $ (29,984 ) $ — Content library 4,700 — 4,700 — — — Total $ 44,684 $ (30,817 ) $ 13,867 $ 29,984 $ (29,984 ) $ — During 2018, the Company recorded additional finite-lived intangible assets totaling $7.5 million and $7.2 million , related to developed technology from the acquisitions of Workpop Inc. and Grovo Learning, Inc, respectively. (see Note 3 ). Total amortization expense from finite-lived intangible assets was $0.8 million , $7.4 million and $9.3 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. The amortization expense recognized was related to developed technology and was recorded in cost of revenue. The following table presents the Company's estimate of remaining amortization expense for finite-lived intangible assets that existed as of December 31, 2018 (in thousands): 2019 2020 2021 2022 2023 and thereafter Estimated remaining amortization expense $ 4,188 $ 4,188 $ 3,355 $ 855 $ 1,281 The Company evaluates the recoverability of its long-lived assets with finite useful lives, including intangible assets, for impairment whenever events or changes in circumstances indicate that the carrying amounts may not be recoverable. There were no impairment charges related to identifiable intangible assets in the years ended December 31, 2018 , 2017 and 2016 . Goodwill The carrying amount of goodwill as of December 31, 2018 was $47.5 million . Additions in 2018 of $20.8 million resulted from the acquisitions of Workpop Inc. and Grovo Learning, Inc. The carrying amount of goodwill as of December 31, 2017 was $25.9 million . Based on the results of the annual impairment test, no impairment of goodwill existed at December 31, 2018 or 2017 .

Other Balance Sheet Amounts

Other Balance Sheet Amounts	12 Months Ended
	Dec. 31, 2018
Balance Sheet Related Disclosures [Abstract]
Other Balance Sheet Amounts	OTHER BALANCE SHEET AMOUNTS The balance of property and equipment, net is as follows (in thousands): Useful Life December 31, 2018 2017 Computer equipment and software 3 – 5 years $ 52,055 $ 38,838 Build to suit property 25 years 51,058 — Furniture and fixtures 7 years 4,367 3,855 Leasehold improvements 2 – 6 years 9,987 10,046 Renovation in progress n/a 1,984 58 119,451 52,797 Less: accumulated depreciation and amortization (42,197 ) (31,980 ) Total property and equipment, net $ 77,254 $ 20,817 Depreciation expense for the years ended December 31, 2018 , 2017 and 2016 was $10.2 million , $10.3 million , $9.9 million , respectively. The balance of accrued expenses is as follows (in thousands): December 31, 2018 2017 Accrued compensation $ 31,799 $ 23,056 Accrued commissions 13,856 12,401 Other accrued expenses 14,051 19,071 Accrued interest $ 8,625 $ 3,000 Total accrued expenses $ 68,331 $ 57,528

Fair Value of Financial Instrum

Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	FAIR VALUE OF FINANCIAL INSTRUMENTS Fair value represents the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Observable inputs are based on market data obtained from independent sources. The fair value hierarchy is based on the following three levels of inputs, of which the first two are considered observable and the last one is considered unobservable: • Level 1 – Quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. • Level 2 – Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. • Level 3 – Unobservable inputs. Assets and liabilities measured at fair value on a recurring basis included the following as of December 31, 2018 and 2017 (in thousands): December 31, 2018 December 31, 2017 Fair Value Level 1 Level 2 Level 3 Fair Value Level 1 Level 2 Level 3 Cash equivalents $ 129,172 $ 129,172 $ — $ 368,859 $ 358,859 $ 10,000 $ — Corporate bonds 58,033 — 58,033 — 74,648 — 74,648 — U.S. treasury securities 138,726 — 138,726 — 188,880 — 188,880 — Commercial paper 7,973 — 7,973 — — — — — $ 333,904 $ 129,172 $ 204,732 $ — $ 632,387 $ 358,859 $ 273,528 $ — At December 31, 2018 and 2017 , cash equivalents of $129.2 million and $358.9 million , respectively, consisted of money market funds with original maturity dates of three months or less backed by U.S. Treasury bills. As of December 31, 2018 , corporate bonds, U.S. treasury securities and commercial paper were classified within Level 2 of the fair value hierarchy. The bonds were valued using information obtained from pricing services, which obtained quoted market prices from a variety of industry data providers, security master files from large financial institutions, and other third-party sources. The Company performed supplemental analysis to validate information obtained from its pricing services. As of December 31, 2018 , no adjustments were made to such pricing information. Convertible Notes The Company’s 2021 Notes described below, are shown in the accompanying consolidated balance sheets at their original issuance value, net of unamortized discount and debt issuance costs, and are not remeasured to fair value each period. The approximate fair value of the Company’s 2021 Notes as of December 31, 2018 was $415 million . The fair value of the 2021 Notes was estimated on the basis of quoted market prices of similar instruments, which, due to the lack of trading activity, are considered Level 2 in the fair value hierarchy.

Debt and Other Financing Arrang

Debt and Other Financing Arrangements	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Debt and Other Financing Arrangements	DEBT AND OTHER FINANCING ARRANGEMENTS 2018 Convertible Notes In 2013, the Company issued convertible notes (the “2018 Notes”) raising gross proceeds of $253.0 million . The 2018 Notes bore interest at a rate of 1.50% per year payable semi-annually in arrears on January 1 and July 1 of each year, commencing January 1, 2014. On July 1, 2018, the 2018 Notes matured and the $253.0 million principal amount due was repaid. The 2018 Notes are no longer outstanding. In accounting for the 2018 Notes at issuance, the Company separated the 2018 Notes into debt and equity components pursuant to the accounting standards for convertible debt instruments that may be fully or partially settled in cash upon conversion. The fair value of the debt component was estimated using an interest rate for nonconvertible debt, with terms similar to the 2018 Notes, excluding the conversion feature. The excess of the principal amount of the 2018 Notes over the fair value of the debt component was recorded as a debt discount and a corresponding increase in additional paid-in capital. The debt discount was accreted to interest expense over the term of the 2018 Notes using the interest method. The amount recorded to additional paid-in capital was not to be remeasured as long as it continues to meet the conditions for equity classification. Upon issuance of the $253.0 million of 2018 Notes, the Company recorded $214.3 million to debt and $38.7 million to additional paid-in capital for the debt discount. The Company incurred transaction costs of approximately $7.3 million related to the issuance of the 2018 Notes. In accounting for these costs, the Company allocated the costs to the debt and equity components in proportion to the allocation of proceeds from the issuance of the 2018 Notes to such components. Transaction costs allocated to the debt component of $6.2 million are deferred and amortized to interest expense over the term of the 2018 Notes. The transaction costs allocated to the equity component of $1.1 million were recorded to additional paid-in capital. 2021 Senior Convertible Notes In December 2017, the Company issued $300.0 million principal amount of 5.75% senior convertible notes (the “2021 Notes”) for a purchase price equal to 98% of the principal amount, raising net proceeds of $294.0 million . The 2021 Notes are governed by an Indenture, dated December 8, 2017 between the Company and U.S. Bank National Association, as trustee (the “2017 Indenture”). The 2021 Notes mature on July 1, 2021, unless earlier repurchased or converted, and bear interest at a rate of 5.75% per year payable semi-annually in arrears on January 1 and July 1 of each year, commencing January 1, 2018. The 2021 Notes are convertible at an initial conversion rate of 23.8095 shares of the Company’s common stock per $1,000 principal amount of the 2021 Notes, which represents an initial conversion price of $42.00 per share, subject to adjustment for anti-dilutive issuances, voluntary increases in the conversion rate and make-whole adjustments upon a fundamental change. A fundamental change includes a change in control, delisting of the Company’s common stock and a liquidation of the Company. Upon conversion, the Company will deliver the applicable number of the Company’s common stock and cash in lieu of any fractional shares. Holders of the 2021 Notes may convert their 2021 Notes at any time prior to the close of business on the scheduled trading day immediately preceding the maturity date, subject to a restricted period through December 2018. The holders of the 2021 Notes may require the Company to repurchase all or a portion of their 2021 Notes at a cash repurchase price equal to 100% of the principal amount of the Notes being repurchased, plus the remaining scheduled interest through and including the maturity date, upon a fundamental change and events of default, including non-payment of interest or principal and other obligations under the 2017 Indenture. The 2021 Notes were issued at a two percent discount and were accounted for as debt upon issuance. The Company recorded $300.0 million of debt and $6.0 million for the debt discount. The debt discount is accreted to interest expense over the term of the 2021 Notes using the interest method. The Company incurred debt issuance costs of $9.2 million that were deferred and will be amortized to interest expense over the term of the 2021 Notes. The Company agreed to register the resale of the 2021 Notes and the shares of common stock issuable upon conversion of the 2021 Notes. A registration statement on Form S-3 relating to such securities was filed with the U.S. Securities and Exchange Commission by the Company on August 7, 2018. 2018 Notes and 2021 Notes The net carrying amounts of the liability components of the 2018 Notes and 2021 Notes as of December 31, 2018 and 2017 consists of the following (in thousands): December 31, 2018 December 31, 2017 Principal amount $ 300,000 $ 553,000 Unamortized debt discount (4,348 ) (10,190 ) Net carrying amount before unamortized debt issuance costs 295,652 542,810 Unamortized debt issuance costs (6,685 ) (9,617 ) Net carrying value $ 288,967 $ 533,193 The effective interest rate of the liability component is 6.4% for the 2021 Notes. The following table presents the interest expense recognized related to the 2018 Notes and the 2021 Notes for years ended December 31, 2018 , 2017 and 2016 (in thousands): Years Ended December 31, 2018 2017 2016 Contractual interest expense at 1.50% and 5.75% per annum $ 19,147 $ 4,897 $ 3,795 Amortization of debt issuance costs 3,086 1,472 1,263 Accretion of debt discount 5,843 8,360 7,867 Total $ 28,076 $ 14,729 $ 12,925 Net proceeds of approximately $245.7 million and $284.9 million from the 2018 Notes and the 2021 Notes, respectively. The Company used approximately $49.5 million of the net proceeds of the 2018 Notes offering to pay the cost of the Note Hedges described below, which was partially offset by $23.2 million of the proceeds from the Company’s sale of the Warrants also described below. Note Hedges Concurrent with the 2018 Notes that were issued in 2013, the Company entered into note hedges (the “Note Hedges”) with certain bank counterparties, with respect to its common stock. The Company paid $49.5 million for the Note Hedges. The Note Hedges cover approximately 4.7 million shares of the Company’s common stock at a strike price of $54.04 per share and were exercisable by the Company upon conversion of the 2018 Notes. The Note Hedges were intended to reduce the potential economic dilution upon conversion of the 2018 Notes in the event that the fair value per share of the Company’s common stock at the time of exercise was greater than the conversion price of the 2018 Notes. On July 1, 2018, the Note Hedges expired upon the maturity of the 2018 Notes. Warrants Separately and concurrently with the entry by the Company into the Note Hedges in 2013, the Company entered into warrant transactions, whereby it sold warrants to the same bank counterparties as the Note Hedges to acquire up to 4.7 million shares of the Company’s common stock at a strike price of $80.06 per share (the “Warrants”), subject to anti-dilution adjustments. The Company received proceeds of $23.2 million from the sale of the Warrants. The Warrants expire at various dates during 2018 and 2019. As of December 31, 2018 , 3.7 million shares of the Warrants expired and 0.9 million shares were outstanding. If the fair value per share of the Company’s common stock exceeds the strike price of the Warrants, the Warrants will reduce diluted earnings per share to the extent that the calculation does not have an anti-dilutive effect. The amounts paid and received for the Note Hedges and the Warrants have been recorded in additional paid-in capital. The fair value of the Note Hedges was not and the Warrants are not remeasured through earnings each reporting period.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Stockholders' Equity	STOCKHOLDERS ’ EQUITY Capitalization As of December 31, 2018 , the Company’s authorized stock consists of 1,000,000,000 shares of common stock, par value of $0.0001 per share, and 50,000,000 shares of preferred stock, par value of $0.0001 per share. No shares of preferred stock were issued or outstanding at December 31, 2018 and 2017. Share Repurchase Program In November 2017, the Company’s board of directors authorized a $100.0 million share repurchase program of its common stock. The Company may repurchase its common stock for cash in the open market in accordance with applicable securities laws. During the year ended December 31, 2018 , the Company repurchased 1.7 million shares of its common stock at an average cost of $46.85 per share for a total expenditure of $77.4 million , which completed the share repurchase program. The following is a summary of the Company's stock repurchases under its $100.0 million share repurchase program as of December 31, 2018 (in thousands, except per share information): Period # of Shares Repurchased Average Price per Share Total Expenditures November 8, 2017 - December 31, 2017 635 $ 35.55 $ 22,599 January 1, 2018 - March 31, 2018 423 $ 37.84 16,024 April 1, 2018 - June 30, 2018 444 $ 46.66 20,718 July 1, 2018 - September 30, 2018 300 $ 53.82 16,143 October 1, 2018 - December 31, 2018 484 $ 50.59 24,516 Total 2,286 $ 43.71 $ 100,000

Stock-Based Awards

Stock-Based Awards	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Awards	STOCK-BASED AWARDS 1999 and 2009 Plans In November 1999, the Company adopted the 1999 Stock Plan (“1999 Plan”) as amended. In January 2009, the Company adopted the 2009 Plan (“2009 Plan”) as amended. Stock options granted under the 1999 and 2009 Plans may be incentive stock options or non-statutory stock options. At December 31, 2018 , no new shares are issuable under the 1999 and 2009 Plans. 2010 Plan In March 2011, upon the completion of the Company’s initial public offering, the Company adopted the 2010 Plan and determined that it will no longer grant any additional awards under the 1999 Plan and the 2009 Plan. However, the 1999 Plan and the 2009 Plan continue to govern the terms and conditions of the outstanding awards previously granted under each respective plan. Upon the adoption of the 2010 Plan, the maximum aggregate number of shares issuable thereunder was 3,680,480 shares, plus (i) any shares subject to stock options or similar awards granted under the 1999 Plan or 2009 Plan prior to March 16, 2011 that expire or otherwise terminate without having been exercised in full and (ii) shares issued pursuant to awards granted under the 1999 Plan and 2009 Plan that are forfeited to or repurchased by the Company after March 16, 2011, with the maximum number of shares to be added to the 2010 Plan from the 1999 Plan and 2009 Plan equal to 5,614,369 shares of common stock. In addition, the number of shares available for issuance under the 2010 Plan will be annually increased on the first day of each fiscal year beginning with 2012, by an amount equal to the lesser of 5,500,000 shares, 4.5% of the outstanding shares of the Company’s common stock as of the last day of the immediately preceding fiscal year, or such other amount as the Company’s Board of Directors determines. Shares issued pursuant to awards under the 2010 Plan that are repurchased by the Company or that expire or are forfeited, as well as shares used to pay the exercise price of an award or to satisfy the minimum tax withholding obligations related to an award, will become available for future grant or sale under the 2010 Plan. In addition, to the extent that an award is paid out in cash rather than shares, such cash payment will not reduce the number of shares available for issuance under the 2010 Plan. The 2010 Plan permits the grant of incentive stock options to employees and the grant of non-statutory stock options, restricted stock, restricted stock units, stock appreciation rights, performance units and performance shares to the Company’s employees, directors and consultants. Under the 2010 Plan, 4,145,181 shares remained available for issuance, at December 31, 2018 . Stock Options The exercise price of stock options granted under the 2010 Plan must equal at least the fair market value of the Company’s common stock on the date of grant. The term of an incentive stock option may not exceed ten years ; provided, however, that an incentive stock option held by a participant who owns more than 10% of the total combined voting power of all classes of the Company’s stock, may not have a term in excess of five years and must have an exercise price of at least 110% of the fair market value of the Company’s common stock on the grant date. Restricted Stock Units The Company may also grant restricted stock units under the 2010 Plan. The fair value of each restricted stock unit granted is equal to the grant date fair market value of the Company’s common stock. The payment of restricted stock units may be in the form of cash, shares, or in a combination thereof, as determined by the Board of Directors. During 2018 , the Company granted 2,227,182 restricted stock units under the 2010 Plan, containing service conditions. Performance Units/Performance Shares The Company may also grant performance units and performance shares under the 2010 Plan. Performance units and performance shares are awards that will result in a payment to a participant only if performance goals for a predetermined period, established by the Board of Directors, are achieved or the awards otherwise vest. The fair value of each performance unit and performance share awarded is equal to the grant date fair value of the Company’s common stock when the performance goals are defined solely by reference to the Company’s own operations. The fair value of each performance unit and performance award that contain performance goals tied to performance of the Company’s common stock is estimated using a Monte-Carlo simulation. The payment of performance units and performance shares may be in the form of cash, shares, or a combination thereof, as determined by the Board of Directors. Employee Stock Purchase Plan Under the Company’s 2010 Employee Stock Purchase Plan (“ESPP”) eligible employees are granted the right to purchase shares at the lower of 85% of the fair value of the stock at the time of grant or 85% of the fair value at the time of exercise. The right to purchase shares is granted twice yearly for six month offering periods in June and December and exercisable on or about the succeeding December and June, respectively, on each year. Under the ESPP, 3,438,935 shares remained available for issuance, at December 31, 2018 . The Company recognized compensation expense related to the ESPP of $1.9 million , $1.6 million and $1.4 million for the years ended December 31, 2018 , 2017 and 2016, respectively. Stock Options The Company has granted stock options, which vest upon meeting service conditions. The following table summarizes the stock option activity which contain only service conditions, under the Company’s 1999, 2009 and 2010 Plans (in thousands, except per share and term information): Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (1) Outstanding, December 31, 2017 5,432 $ 32.73 5.3 $ 42,282 Granted — — Exercised (1,472 ) 32.48 Forfeited (132 ) 44.59 Outstanding, December 31, 2018 3,828 32.41 4.1 70,436 Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term Aggregate Intrinsic Value (1) Exercisable at December 31, 2018 3,777 $ 32.38 4.0 $ 69,658 Vested and expected to vest at December 31, 2018 3,826 32.41 4.1 70,405 (1) Based on the Company’s closing stock price of $50.43 on December 31, 2018 and $35.33 on December 31, 2017. The following table summarizes information about stock options, which contain only service conditions, under the Company’s equity incentive plans at December 31, 2018 (in thousands except term information): Options Outstanding at December 31, 2018 Options Exercisable at December 31, 2018 Number of Options Weighted Average Remaining Contractual Term (in years) Number of Options Weighted Average Remaining Contractual Term (in years) Range of Exercise Prices $0.34 to $1.65 29 1.2 29 1.2 $5.93 to $8.88 618 1.9 617 1.9 $12.54 to $15.41 119 2.7 119 2.7 $16.24 to $18.82 223 3.0 223 3.0 $20.85 to $23.94 398 3.4 398 3.4 $27.55 to $31.44 129 4.7 129 4.7 $31.64 to $36.15 546 5.5 495 5.5 $38.03 to $45.76 656 4.9 656 4.9 $46.20 to $56.05 1,110 4.8 1,110 4.8 3,828 4.1 3,776 4.0 The total intrinsic value of options exercised during the years ended December 31, 2018 , 2017 and 2016 was $25.8 million , $9.2 million and $18.2 million , respectively. The total grant date fair value of stock options vested during the years ended December 31, 2018 , 2017 and 2016 was $5.5 million , $15.4 million and $24.3 million , respectively. The Company recognized compensation expense related to stock options of $4.8 million , $14.0 million and $23.0 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. Unrecognized compensation expense relating to stock options was $0.6 million at December 31, 2018 which is expected to be recognized over a weighted-average period of 0.7 years. The aggregate grant date fair value of stock options granted for the year ended December 31, 2016 was $1.8 million . There were no stock options granted for the years ended December 31, 2018 and 2017 . Restricted Stock Units Restricted stock unit activity for the year ended December 31, 2018 under the Company’s equity incentive plans is summarized as follows (shares in thousands): Number of Shares Weighted Average Grant Date Fair Value Outstanding at December 31, 2017 3,790 $ 37.22 Granted 2,227 46.17 Forfeited (530 ) 39.07 Vested (1,370 ) 36.87 Outstanding at December 31, 2018 4,117 $ 41.94 The weighted-average grant date fair value of the restricted stock units granted during the years ended December 31, 2018 , 2017 and 2016 was $46.17 , $37.99 and $37.49 , respectively. The total fair value of restricted stock units vested as of the vesting dates during the years ended December 31, 2018 , 2017 and 2016 was $49.9 million , $37.2 million and $24.7 million . The Company recognized compensation expense related to restricted stock units of $53.2 million , $44.1 million and $31.9 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. Unrecognized compensation expense related to unissued shares of the Company’s common stock subject to unvested restricted stock units was $127.8 million at December 31, 2018 , which is expected to be recognized as expense over the weighted-average period of 2.9 years. Performance-Based Restricted Stock Units The Compensation Committee designed an annual equity compensation structure to further align the compensation levels of certain executives to the performance of the Company through the issuance of performance-based restricted stock units. The number of shares of the Company’s common stock issuable upon the vesting of these performance-based restricted stock unit awards is based upon the Company meeting composite revenue and cash flow growth targets determined at the time of their grant. The total amount of compensation expense recognized is based on the number of shares that the Company determines are probable of vesting. The estimate will be made each reporting period and determined by the Company’s actual and projected revenue and cash flow performance and other factors that may impact the likelihood of vesting. The compensation expense will be recognized over the vesting term of the awards. The following table summarizes the Company’s issuances of awards under the new compensation award structure at December 31, 2018 : Grant Date Performance Measures Vesting Term Performance Period # of Shares at Target # of Shares at Maximum Grant Date Fair Value per share # of Shares Outstanding at Target # of Shares Outstanding at Maximum July 2016 (1) (a) the Company meeting certain revenue and cash flow targets through December 31, 2018 and (b) the recipient continuing to provide services to the Company through the end of June 2019 Three years Fiscal years 2016, 2017 and 2018 166,600 499,800 $ 38.67 — — March 2017 (a) the Company meeting certain revenue and cash flow targets through December 31, 2019 and (b) the recipient continuing to provide services to the Company through the end of March 2020 Three years Fiscal years 2017, 2018 and 2019 185,270 555,810 $ 41.73 149,490 448,470 February 2018 (a) the Company meeting certain combined subscription revenue and unlevered cash flow margin targets for the year ending December 31, 2020 and (b) the recipient continuing to provide services to the Company through the end of February 2021 Three years Fiscal year 2020 121,764 304,410 $ 40.64 121,764 304,410 February 2018 (a) the Company meeting certain combined subscription revenue and unlevered cash flow margin targets for each of the years ending December 31, 2020, December 31, 2021, and December 31, 2022 and (b) the recipient continuing to provide services to the Company through each respective vest date at the end of February 2020, 2021 and 2022 Five years (2) Fiscal years 2020, 2021 and 2022 411,412 1,028,530 $ 40.64 411,412 1,028,530 April 2018 (a) the Company meeting certain combined subscription revenue and unlevered cash flow margin targets for the year ending December 31, 2020 and (b) the recipient continuing to provide services to the Company through the beginning of April 2021 Three years Fiscal year 2020 3,572 8,930 $ 39.54 3,572 8,930 April 2018 (a) the Company meeting certain combined subscription revenue and unlevered cash flow margin targets for each of the years ending December 31, 2020, December 31, 2021, and December 31, 2022 and (b) the recipient continuing to provide services to the Company through each respective vest date at the beginning of April 2020, 2021 and 2022 Five years (2) Fiscal years 2020, 2021 and 2022 53,572 133,930 $ 39.54 53,572 133,930 (1) In December 2018, based on the performance of the Company’s results for certain revenue and cash flow targets, the Company determined it had not achieved the required performance level for the performance-based awards granted in July 2016, which resulted in none of the shares being issued. (2) One-third of the total eligible shares shall vest on each of the third, fourth and fifth anniversaries of the grant date. This award is a one-time equity award intended to cover expected grant levels over a three-year period. In exchange, the Compensation Committee does not plan to grant any additional equity awards to recipients of this award until 2021. The Company recognized compensation expense related to all performance-based awards in the aggregate amount of $5.5 million , $11.2 million and $2.6 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. Unrecognized compensation expense related to unvested performance-based restricted stock units was $18.4 million at December 31, 2018 , which is expected to be recognized as expense over the weighted-average period of 3.0 years. Stock-Based Compensation Stock-based compensation expense related to stock options, restricted stock units, the ESPP and performance-based restricted stock units is included in the following line items in the accompanying consolidated statements of operations for the years ended December 31, 2018 , 2017 and 2016 (in thousands): Years Ended December 31, 2018 2017 2016 Cost of revenue $ 4,218 $ 4,904 $ 4,732 Sales and marketing 24,440 28,427 25,642 Research and development 11,800 9,630 7,586 General and administrative 19,872 22,869 16,739 Restructuring 6,227 — — Total $ 66,557 $ 65,830 $ 54,699 In certain instances the Company is responsible for payroll taxes related to stock options exercised or the underlying shares sold by its employees. The Company accrues its obligations at the time of the exercise of the stock options or the sale of the underlying shares.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (the “Tax Act”) was signed into law making significant changes to the Internal Revenue Code of 1986, as amended. Changes attributed to the Tax Act include, but are not limited to, a corporate tax rate decrease from 34% to 21% effective for tax years beginning after December 31, 2017, further limitation on deductibility of interest expense, the transition of U.S international taxation from a worldwide tax system to a territorial system, creation of a new provision designed to tax global low-tax intangible income ("GILTI), and a one-time transition tax on the mandatory deemed repatriation of cumulative foreign earnings as of December 31, 2017. The SEC staff issued Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of The Tax Cuts and Jobs Act ("SAB") 118, which allowed the Company to record provisional amounts during a measurement period not to exceed beyond one year of the enactment date. The Company completed its analysis to determine the effect of the Tax Act and recorded immaterial adjustments as of December 31, 2018. The components of the Company’s loss before provision (benefit) for income taxes are as follows (in thousands): Years Ended December 31, 2018 * 2017 2016 United States $ (21,174 ) $ (32,853 ) $ (39,107 ) Foreign (10,073 ) (26,736 ) (26,523 ) Loss before provision for income taxes $ (31,247 ) $ (59,589 ) $ (65,630 ) * See Note 2 for summary of adjustments in relation to the adoption of ASC 606. The components of the provision (benefit) for income taxes attributable to continuing operations are as follows (in thousands): Years Ended December 31, 2018 2017 2016 Current income tax provision: Federal $ — $ — $ — State 204 114 105 Foreign 2,514 1,580 1,838 Total current income tax provision 2,718 1,694 1,943 Deferred income tax benefit: Federal — — — State — — — Foreign (123 ) 52 (736 ) Total deferred income tax benefit (123 ) 52 (736 ) Total income tax provision (benefit) $ 2,595 $ 1,746 $ 1,207 On a consolidated basis, the Company has incurred operating losses and has recorded a full valuation allowance against its United States, United Kingdom, New Zealand, Hong Kong and Brazil deferred tax assets for all periods to date and, accordingly, has not recorded a provision (benefit) for income taxes for any of the periods presented other than a provision (benefit) for certain foreign and state income taxes. Certain foreign subsidiaries and branches of the Company provide intercompany services and are compensated on a cost-plus basis, and therefore, have incurred liabilities for foreign income taxes in their respective jurisdictions. The differences in the total provision for income taxes that would result from applying the 21% federal statutory rate beginning in 2018 and 34% federal statutory rate prior to 2018 to loss before provision for income taxes and the reported provision for income taxes are as follows (in thousands): Years Ended December 31, 2018 2017 2016 U.S. Federal tax benefit at statutory rates $ (6,562 ) $ (20,260 ) $ (22,310 ) State income taxes, net of federal tax benefit (248 ) (806 ) (855 ) Foreign rate differential 2,764 5,220 3,711 Stock based compensation 3,029 3,182 4,467 Other permanent differences 280 (494 ) (750 ) Deferred adjustments / U.S. rate change 1,430 7,811 — Other 130 262 1,494 Valuation allowance 1,772 6,831 15,450 Total income tax (benefit) provision $ 2,595 $ 1,746 $ 1,207 Major components of the Company’s deferred tax assets (liabilities) at December 31, 2018 and 2017 are as follows (in thousands): December 31, 2018 2017 Deferred tax assets: Accrued expenses $ 2,353 $ 2,371 Long-lived intangible assets and fixed assets — basis difference 22,947 19,884 Net operating loss carryforwards 82,017 80,615 Stock-based compensation 15,172 16,886 Deferred revenue 2,861 2,739 Convertible note hedge — 1,467 Other 4,557 2,721 Total deferred tax assets 129,907 126,683 Valuation allowance (117,058 ) (118,606 ) Deferred tax assets, net of valuation allowance 12,849 8,077 Deferred tax liabilities: Prepaid expenses and deferred commissions (10,831 ) (5,672 ) Convertible note discount — (1,074 ) Other (976 ) (410 ) Total deferred tax liabilities (11,807 ) (7,156 ) Net deferred tax assets (liabilities) $ 1,042 $ 921 At December 31, 2018 , the Company had federal, state and foreign net operating losses of approximately $261.8 million , $269.5 million and $84.8 million , respectively. The federal net operating loss carryforward will begin expiring in 2022, the state net operating loss carryforward will begin expiring in 2019, and the foreign net operating loss has an unlimited carryforward period. The Internal Revenue Code of 1986, as amended, imposes substantial restrictions on the utilization of net operating losses in the event of an “ownership change” of a corporation. Accordingly, a company’s ability to use net operating losses may be limited as prescribed under Internal Revenue Code Section 382 (“IRC Section 382”). Events which may cause limitations in the amount of the net operating losses that the Company may use in any one year include, but are not limited to, a cumulative ownership change of more than 50% over a three-year period. Due to the effects of historical equity issuances, the Company has determined that the future utilization of a portion of its net operating losses is limited annually pursuant to IRC Section 382. The Company has determined that none of its net operating losses will expire because of the annual limitation. The Company has recorded a full valuation allowance against its otherwise recognizable United States, United Kingdom, New Zealand, Hong Kong and Brazil deferred income tax assets as of December 31, 2018 . Management has determined, after evaluating all positive and negative historical and prospective evidence, that it is more likely than not that these assets will not be realized. The net increase to the valuation allowance of $(1.5) million , $6.8 million and $15.5 million for the years ended December 31, 2018 , 2017 and 2016 , respectively, was primarily due to additional net operating losses generated by the Company. Deferred income taxes have not been provided on the undistributed earnings of the Company’s foreign subsidiaries because the Company’s practice and intent is to permanently reinvest these earnings. The cumulative amount of such undistributed earnings was $3.1 million and $3.3 million at December 31, 2018 and December 31, 2017 , respectively. Any future distribution of these non-U.S. earnings may subject the Company to state income taxes, as adjusted for tax credits, and foreign withholding taxes that the Company estimates would be $0.1 million and $0.1 million at December 31, 2018 and 2017 , respectively. The Company determined that the transition tax on any undistributed earnings that existed as of December 31, 2018 will be zero . A reconciliation of the beginning and ending amount of unrecognized tax benefits for the years ended December 31, 2018 , 2017 and 2016 is as follows (in thousands): Years Ended December 31, 2018 2017 2016 Balance at January 1 $ 1,271 $ 276 $ 276 Additions for tax positions related to the current year 131 995 — Balance at December 31 $ 1,402 $ 1,271 $ 276 The provision for uncertain tax positions relates to business in territories outside of the United States. The Company’s policy is to classify interest and penalties on uncertain tax positions as a component of tax expense. An immaterial amount of interest and penalties on unrecognized tax benefits were accrued during the 2018 tax year. The amount of accrued interest and penalties on unrecognized tax benefits was immaterial, as of December 31, 2018 and 2017 . The Company does not expect the change in uncertain tax positions to have a material impact on its financial position, results of operations or liquidity. The recognition of previously unrecognized tax benefits on uncertain tax positions would result in a $1.4 million tax benefit. The Company believes it is reasonably possible that within the next twelve months the Company may resolve certain matters related to the years under examination, which may result in reductions of the Company's unrecognized tax benefits and income tax expense of up to $1.2 million . The Company is subject to United States federal income tax as well as to income tax in multiple state and foreign jurisdictions, including the United Kingdom. Federal income tax returns of the Company are subject to IRS examination for the 2015 through 2018 tax years. State income tax returns are subject to examination for the 2014 through 2018 tax years. At December 31, 2018, the Company is not impacted by the Global Intangible Low Taxed Income ("GILTI") provisions. There are no ongoing audits in any significant foreign tax jurisdictions.

Restructuring Costs

Restructuring Costs	12 Months Ended
	Dec. 31, 2018
Restructuring and Related Activities [Abstract]
Restructuring Costs	RESTRUCTURING COSTS In December 2017, as part of the Company’s strategic plan to accelerate revenue growth and increase operating margins, the Company approved a restructuring plan to reduce the headcount of the Company’s global service delivery team, as well as the headcount of some of its sales teams, representing a total workforce reduction of approximately six percent. The restructuring is part of the Company’s renewed focus on recurring, or subscription-based, revenue growth and driving cost reductions to accelerate the growth of its operating margins and free cash flow. During the year ended December 31, 2018 and December 31, 2017 , the Company continued with a strategic plan to reduce professional service and sales headcount, resulting in $8.9 million and $1.5 million of restructuring expenses, respectively, which was recorded in “Restructuring” in the accompanying consolidated statements of operations. For the year ended December 31, 2018 , the restructuring expense consisted primarily of stock-based compensation expense of $6.2 million , and $2.7 million of payroll-related costs. The stock-based compensation expense relates to accelerated vesting for impacted employees. For the year ended December 31, 2017 , the restructuring expense consisted primarily of payroll-related costs, such as severance, outplacement costs and continuing healthcare coverage, associated with employee terminations. The restructuring plan was completed as of December 31, 2018 .

Segment and Geographic Informat

Segment and Geographic Information	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Segment and Geographic Information	SEGMENT AND GEOGRAPHIC INFORMATION The Company’s management has determined that the Company operates in one segment as it only reports financial information on an aggregate and consolidated basis to its chief executive officer, who is the chief operating decision maker. The Company presents its entity-wide information in the tables below. The following table sets forth the Company’s sources of revenue (dollars in thousands): At or For Year Ended December 31, 2018 * 2017 2016 Subscription revenue $ 473,052 $ 396,764 $ 339,756 Percentage of subscription revenue to total revenue 87.9 % 82.3 % 80.3 % Professional services revenue $ 64,839 $ 85,221 $ 83,368 Percentage of professional services revenue to total revenue 12.1 % 17.7 % 19.7 % $ 537,891 $ 481,985 $ 423,124 * See Note 2 for summary of adjustments in relation to the adoption of ASC 606. Revenue by geographic region, which is generally based on the address of the Company’s clients as defined in their master subscription agreements, is set forth below (in thousands): Years Ended December 31, 2018 * 2017 2016 Revenue United States $ 343,205 $ 313,729 $ 284,657 All other countries 194,686 168,256 138,467 Total revenue $ 537,891 $ 481,985 $ 423,124 * See Note 2 for summary of adjustments in relation to the adoption of ASC 606. Property and equipment by region is set forth below (in thousands): December 31, 2018 2017 Property and equipment, net United States $ 69,550 $ 16,468 United Kingdom 3,558 3,378 All other countries 4,146 971 Total property and equipment, net $ 77,254 $ 20,817

401(k) Savings Plan

401(k) Savings Plan	12 Months Ended
	Dec. 31, 2018
Retirement Benefits [Abstract]
401(k) Savings Plan	401(K) SAVINGS PLAN The Company has a defined contribution savings plan (the “Plan”) under Section 401(k) of the Internal Revenue Code. The Plan covers substantially all employees who meet minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. Company contributions to the Plan may be made at the discretion of the Board of Directors. The Plan provides for a Company matching contribution in an amount equal to 50% of an employee’s contributions up to $2,400 per year, which vests fully after the four th year of employment. The Company incurred approximately $2.0 million , $2.0 million and $1.9 million of matching contribution expenses related to the Plan during the years ended December 31, 2018 , 2017 and 2016, respectively.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES Leases The Company has various non-cancelable operating leases for its offices and its managed hosting facilities and services. These leases expire at various times through 2025. Certain lease agreements contain renewal options, rent abatement and escalation clauses. The Company recognizes rent expense on a straight-line basis over the lease term, commencing when the Company takes possession of the property. Certain of the Company’s office leases entitle the Company to receive a tenant allowance from the landlord. The Company records tenant allowances as a deferred rent credit, which the Company amortizes on a straight-line basis, as a reduction of rent expense, over the term of the underlying lease. Total rent expense under operating leases was approximately $9.8 million , $8.0 million and $7.8 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. Future minimum lease payments under non-cancelable operating leases at December 31, 2018 are as follows (in thousands): Operating Leases (1) 2019 $ 11,576 2020 14,162 2021 14,277 2022 14,823 2023 14,710 Thereafter 17,961 Total minimum lease payments $ 87,509 (1) The table above includes future minimum lease payments for the Company's facility financing obligation as follows: 2019: $4.8 million ; 2020: $4.9 million ; 2021: $4.9 million ; 2022: $5.3 million ; 2023 and thereafter: $21.7 million . Letters of Credit The Company maintains standby letters of credit in association with other contractual arrangements. Total letters of credit outstanding at December 31, 2018 and December 31, 2017 was $7.7 million and $1.4 million , respectively. Other Commitments As of December 31, 2018 , the Company had software subscription and other miscellaneous agreements with various service providers with obligations of approximately $17.8 million in 2019, $8.8 million in 2020 and $2.8 million in 2021. Guarantees and Indemnifications The Company has made guarantees and indemnities under which it may be required to make payments to a guaranteed or indemnified party, in relation to certain transactions, including revenue transactions in the ordinary course of business. The Company is obligated to indemnify its directors and officers to the maximum extent permitted under the laws of the State of Delaware. However, the Company has a directors and officers insurance policy that may reduce its exposure in certain circumstances and may enable it to recover a portion of future amounts that may be payable, if any. The duration of the guarantees and indemnities varies and, in many cases, is indefinite but subject to statutes of limitations. To date, the Company has made no payments related to these guarantees and indemnities. The Company estimates the fair value of its indemnification obligations as insignificant based on this history and the Company’s insurance coverage and therefore has not recorded any liability for these guarantees and indemnities in the accompanying consolidated balance sheets. Litigation The Company is subject to various legal proceedings and claims that arise in the ordinary course of business. If the Company determines that it is probable that a loss has been incurred and the amount is reasonably estimable, the Company will record a liability. The Company has determined that it does not have any reasonably possible liabilities related to any legal proceedings or claims that would individually or in the aggregate materially adversely affect its financial condition or operating results. Taxes From time to time, various federal, state and other jurisdictional tax authorities undertake review of the Company and its filings. In evaluating the exposure associated with various tax filing positions, the Company accrues charges for possible exposures. The Company believes any adjustments that may ultimately be required as a result of any of these reviews will not be material to its consolidated financial statements.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
Related Party Transactions	RELATED PARTY TRANSACTIONS The Cornerstone OnDemand Foundation (the “Foundation”) empowers communities in the United States and internationally by increasing the impact of the non-profit sector through the utilization of human capital management technology including the Company’s products. The Company’s chief executive officer is on the board of directors of the Foundation. The Company does not direct the Foundation’s activities, and accordingly, the Company does not consolidate the Foundation’s statement of activities with its financial results. During the years ended December 31, 2018 , 2017 and 2016 , the Company provided at no charge certain resources to the Foundation, with approximate values of $3.7 million , $3.4 million and $3.3 million , respectively.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	SUBSEQUENT EVENTS During January 2019, shares issuable under the Company’s 2010 Employee Stock Purchase Plan increased by 588,856 shares and shares issuable under the Company’s 2010 Plan increased by 2,649,855 shares in accordance with the automatic annual increase provisions of such plans. The Compensation Committee has granted or approved performance-based restricted stock units during February 2019. Achievement of the probable target level would result in the issuance of 93,738 shares of the Company’s common stock upon the vesting of the restricted stock units and achievement of the maximum target would result in the issuance of 234,345 shares of the Company’s common stock upon the vesting of the restricted stock units. The performance-based restricted stock units will vest over three years. During January and February 2019, the Compensation Committee has granted or approved restricted stock units covering an aggregate of 251,928 shares of the Company’s common stock which generally vest annually over four years. During February 2019, the Company entered into lease agreements with obligations of approximately $0.5 million in 2019, $1.1 million in 2020, $1.1 million in 2021, 1.1 million in 2022 and 2.0 million in 2023 and thereafter.

Selected Quarterly Data (Unaudi

Selected Quarterly Data (Unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Data (Unaudited)	SELECTED QUARTERLY DATA (UNAUDITED) The following unaudited quarterly consolidated statements of operations for each of the quarters in the years ended December 31, 2018 and 2017 have been prepared on a basis consistent with the Company’s audited annual consolidated financial statements and include, in the opinion of management, all normal recurring adjustments necessary for the fair presentation of the financial information contained in these statements. Quarter Ended (in thousands, except per share data) Mar. 31, June 30, Sept. 30, Dec. 31, Mar. 31, June 30, Sept. 30, Dec. 31, Revenue $ 111,582 $ 116,651 $ 121,796 $ 131,956 $ 133,113 $ 132,517 $ 134,014 $ 138,247 Cost of revenue 33,949 35,321 35,708 37,889 37,020 36,365 36,171 34,793 Gross profit 77,633 81,330 86,088 94,067 96,093 96,152 97,843 103,454 Operating expenses: Sales and marketing 56,894 62,073 60,554 60,750 59,245 59,821 53,215 52,354 Research and development 13,411 14,684 16,389 17,491 15,984 16,325 19,705 24,967 General and administrative 20,476 23,141 21,249 19,723 21,985 22,101 23,128 23,535 Restructuring — — — 1,539 7,725 1,000 221 — Total operating expenses 90,781 99,898 98,192 99,503 104,939 99,247 96,269 100,856 (Loss) income from operations (13,148 ) (18,568 ) (12,104 ) (5,436 ) (8,846 ) (3,095 ) 1,574 2,598 (Loss) income from operations per share, basic and diluted $ (0.23 ) $ (0.33 ) $ (0.21 ) $ (0.09 ) $ (0.15 ) $ (0.05 ) $ 0.03 $ 0.04 Other income (expense): Interest income (expense) and other income (expense), net (2,492 ) (2,333 ) (2,248 ) (3,260 ) (6,837 ) (8,376 ) (3,499 ) (4,767 ) Loss before income tax provision (15,640 ) (20,901 ) (14,352 ) (8,696 ) (15,683 ) (11,471 ) (1,925 ) (2,169 ) Income tax provision (571 ) (364 ) (503 ) (308 ) (533 ) (536 ) (522 ) (1,004 ) Net loss $ (16,211 ) $ (21,265 ) $ (14,855 ) $ (9,004 ) $ (16,216 ) $ (12,007 ) $ (2,447 ) $ (3,173 ) Net loss per share, basic and diluted $ (0.29 ) $ (0.37 ) $ (0.26 ) $ (0.16 ) $ (0.28 ) $ (0.21 ) $ (0.04 ) $ (0.05 ) Weighted average common shares outstanding, basic and diluted 56,642 56,935 57,627 57,826 57,425 57,844 58,699 58,649 * See Note 2 for summary of adjustments in relation to the adoption of ASC 606.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation and Principles of Consolidation	Basis of Presentation and Principles of Consolidation The accompanying consolidated financial statements are presented in accordance with accounting standards generally accepted in the United States of America (“GAAP”), and include the accounts of Cornerstone OnDemand, Inc. and its wholly owned subsidiaries. All significant inter-company transactions and balances have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Actual results could differ from those estimates. On an on-going basis, management evaluates its estimates, including among others those related to: (i) the realization of tax assets and estimates of tax liabilities and reserves, (ii) the recognition and disclosure of contingent liabilities, (iii) the evaluation of revenue recognition criteria, including the determination of standalone value and estimates of the selling price of multiple-deliverables in the Company’s revenue arrangements, (iv) fair values of investments in marketable securities and strategic investments carried at fair value, (v) the fair values of acquired assets and assumed liabilities in business combinations, (vi) the useful lives of property and equipment, capitalized software and intangible assets, (vii) impairment of long-lived assets, (viii) the period of amortization of the commission payments to record to expense and (ix) determination of the number of shares that are probable of vesting for performance-based restricted stock unit awards. These estimates are based on historical data and experience, as well as various other factors that management believes to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying value of assets and liabilities that are not readily apparent from other sources. The Company engages third-party valuation specialists to assist with the allocation of the purchase price in business combinations. Such estimates required the selection of appropriate valuation methodologies and models and significant judgment in evaluating ranges of assumptions and financial inputs.
Business Combinations	Business Combinations The results of businesses acquired in a business combination are included in the Company’s consolidated financial statements from the date of the acquisition. Purchase accounting results in assets and liabilities of an acquired business being recorded at their estimated fair values on the acquisition date. Any excess consideration over the fair value of assets acquired and liabilities assumed is recognized as goodwill. The Company performs valuations of assets acquired and liabilities assumed for an acquisition and allocates the purchase price to its respective net tangible and intangible assets. The Company engages the assistance of valuation specialists in concluding on fair value measurements in connection with determining fair values of assets acquired and liabilities assumed in a business combination.
Revenue Recognition and Cost of Revenue	Cost of Revenue Cost of revenue consists primarily of costs related to hosting our products and delivery of professional services, and includes the following: • personnel and related expenses, including stock-based compensation; • expenses for network-related infrastructure and IT support; • delivery of contracted professional services and on-going client support staff; • payments to external service providers contracted to perform implementation services; • depreciation of data centers and amortization of capitalized software costs, developed technology software license rights, content and licensing fees and referral fees. In addition, the Company allocates a portion of overhead, such as rent, IT costs, depreciation and amortization and employee benefits costs, to cost of revenue based on headcount. Costs associated with providing professional services are recognized as incurred when the services are performed. Out-of-pocket travel costs related to the delivery of professional services are typically reimbursed by the client and are accounted for as both revenue and cost of revenue in the period in which the cost is incurred. Revenue Recognition Effective January 1, 2018, the Company adopted the guidance under Topic 606 on a modified retrospective approach. All balances reported prior to this date are presented under Topic 605. Refer to the discussion under Recently Adopted Accounting Pronouncements below to understand the impacts of adopting Topic 606 on our financial statements. The Company derives its revenue from the following sources: Subscriptions to the Company’s products and other offerings on a recurring basis Clients pay subscription fees for access to the Company’s enterprise human capital management platform, other products and support on a recurring basis. Fees are based on a number of factors, including the number of products purchased, which may include e-learning content, and the number of users having access to a product. The Company generally recognizes revenue from subscriptions ratably over the term of the agreements beginning on the date the subscription service is made available to the client. Subscription agreements are typically three years, billed annually in advance, and non-cancelable, with payment due within 30 days of the invoice date. Professional services and other The Company offers its clients and implementation partners assistance in implementing its products and optimizing their use. Professional services include application configuration, system integration, business process re-engineering, change management and training services. Services are generally billed up-front on a fixed fee basis and to a lesser degree on a time-and-material basis. These services are generally purchased as part of a subscription arrangement and are typically performed within the first several months of the arrangement. Clients may also purchase professional services at any other time. The Company generally recognizes revenue from fixed fee professional services contracts as services are performed based on the proportion performed to date relative to the total expected services to be performed. Revenue associated with time-and-material contracts are recorded as such time-and-materials are incurred. The Company recognizes revenue from contracts with customers based on the following five steps: 1) Identification of the contract, or contracts, with a customer 2) Identification of all performance obligations in the contract 3) Determination of the transaction price 4) Allocation of the transaction price to the performance obligations in the contract 5) Recognition of revenue as the Company satisfies a performance obligation The Company identifies enforceable contracts with a customer when the agreement is signed. The Company accounts for individual performance obligations separately if they are distinct. The transaction price is generally based on fixed fees stated in the contract. The Company excludes from the transaction price any amounts relating to taxes from product sales which are collected from customers and remitted to governmental authorities. If the contract contains a single performance obligation, the entire transaction price is allocated to the single performance obligation. Contracts that contain multiple performance obligations require an allocation of the transaction price to each performance obligation based on a relative standalone selling price basis. The Company is not able to directly observe a standalone selling price for its performance obligations, as the performance obligations are sold separately and within a sufficiently narrow price range only infrequently, and because management has determined that there are no third-party offerings reasonably comparable to the Company’s products. Accordingly, total contract values are allocated to subscriptions to the products and professional services based on the standalone selling price (“SSP”). The determination of SSP requires the Company to make certain estimates and judgments. The Company considers numerous factors, including the nature and complexity of the performance obligations themselves; the geography, market conditions and competitive landscape for the sale; internal costs; and pricing and discounting practices. The Company updates its estimates of SSP on an ongoing basis through internal periodic reviews and as events or circumstances may require. Revenue is recognized at the time the related performance obligation is satisfied by transferring a promised service to a customer. The Company satisfies performance obligations over time. In a limited number of cases, the client’s intended use of a product requires contractually specified enhancements to its underlying features and functionality. In some of these cases, revenue is recognized as a combined single performance obligation on a straight-line basis from the point at which access to the enhanced product(s) have been provided, through the remaining term of the agreement. In other cases where the enhancement is not contractually specified by the customer for its initial use, revenue is recognized separately for the enhancement and the product as a second distinct performance obligation. In such cases where a second performance obligation exists, the enhancement revenue is recognized based on a SSP allocation on a straight-line basis once access to the enhancement has been provided, through the remaining term of the agreement. For arrangements in which the Company resells third-party e-learning training content to clients, revenue is recognized in accordance with accounting guidance as to when to report gross revenue as a principal or report net revenue as an agent. The Company typically recognizes third-party content revenue at the gross amount invoiced to clients as (i) the Company is primarily responsible for hosting the content on the Company's platform for the term of the agreement, (ii) the Company controls the content before access is provided to the customer, and (iii) the Company typically has discretion to establish the price charged. Deferred Revenue The Company records amounts that have been invoiced to its clients in accounts receivable and in either deferred revenue or revenue depending on whether the revenue recognition criteria described above have been met. Deferred revenue that will be recognized during the succeeding twelve-month period from the respective balance sheet date is recorded as current deferred revenue and the remaining portion is recorded as noncurrent. The decrease in the deferred revenue balance for the year ended December 31, 2018 is primarily driven by $301.6 million of revenue recognized that were included in the deferred revenue balances as of January 1, 2018 offset by invoices billed in advance of satisfying performance obligations in accordance with contract payment terms. Transaction Price Allocated to Remaining Performance Obligations As of December 31, 2018 , approximately $876.0 million of revenue is expected to be recognized from remaining performance obligations. This amount mainly comprises subscription revenue, with less than 10% attributable to professional services and other revenue. The Company expects to recognize revenue on approximately two thirds of these remaining performance obligations over the next 18 months , with the balance recognized thereafter. The estimated revenues from the remaining performance obligations do not include uncommitted contract amounts such as (i) amounts which are cancelable by the client without any significant penalty, (ii) future billings for time-and-material contracts, and (iii) amounts associated with optional renewal periods. Sales Commission The Company defers commissions paid to its sales force and related payroll taxes as these amounts are incremental costs of obtaining a contract with a customer and are recoverable from future revenue due to the non-cancelable client agreements that gave rise to the commissions. Commissions for initial contracts are deferred on the consolidated balance sheets and amortized on a straight-line basis over a period of benefit that has been determined to be six years. The Company took into consideration technology and other factors in estimating the benefit period. Sales commissions for renewal contracts are deferred and amortized on a straight-line basis over the related contract renewal period. Amortization expense is included in sales and marketing expenses in the accompanying consolidated statements of operations. The Company generally commences payment of commissions within 45 to 75 days after execution of client agreements.
Research and Development	Research and Development Research and development expenses consist primarily of personnel and related expenses for the Company’s research and development staff, including salaries, benefits, bonuses and stock-based compensation; the cost of certain third-party service providers; and allocated overhead. Research and development expenses, other than software development costs qualifying for capitalization, are expensed as incurred.
Advertising	Advertising Advertising expenses for 2018 , 2017 and 2016 were $7.1 million , $9.0 million and $6.6 million , respectively, and are expensed as incurred and is recorded within Sales and Marketing in the accompanying consolidated statements of operations.
Stock-based Compensation	Stock-Based Compensation The Company accounts for stock-based awards granted to employees and directors by recording compensation expense based on the awards’ estimated fair values. The Company grants stock options and restricted stock units that vest over time based on the continuing employment of the employee, as well as restricted stock units that vest based on meeting certain performance targets. The Company estimates the fair value of its restricted stock units based on the closing price of its common stock as of the date of grant. The Company estimates the fair value of its stock options as of the date of grant using the Black-Scholes option-pricing model. Determining the fair value of stock options under this model requires judgment, including estimating (i) the value per share of the Company's common stock, (ii) volatility, (iii) the term of the awards, (iv) the dividend yield and (v) the risk-free interest rate. The assumptions used in calculating the fair value of stock based awards represent the Company’s best estimates, based on management’s judgment and subjective future expectations. These estimates involve inherent uncertainties. If any of the assumptions used in the model change significantly, stock-based compensation recorded for future awards may differ materially from that recorded for awards granted previously. Beginning in 2017, the Company began estimating expected volatility based solely on its historical volatility as a public company. In previous years, the Company estimated this using the average volatility of similar publicly traded companies as sufficient trading history of the Company’s stock was not available. For purposes of determining the expected term of the awards in the absence of sufficient historical data relating to stock option exercises for the Company, it applies a simplified approach in which the expected term of an award is presumed to be the mid-point between the vesting date and the expiration date of the award. The risk-free interest rate for periods within the expected life of an award, as applicable, is based on the United States Treasury yield curve in effect during the period the award was granted. The estimated dividend yield is zero, as the Company has not declared dividends in the past and does not currently intend to declare dividends in the foreseeable future. Once the Company has determined the estimated fair value of its stock-based awards, it recognizes the portion of that value that corresponds to the portion of the award that is ultimately expected to vest, taking estimated forfeitures into account. This amount is recognized as an expense over the vesting period of the award using the straight-line method for awards which contain only service conditions, and using the graded vesting method based upon the probability of the performance condition being met for awards which contain performance conditions. The Company estimates forfeitures based upon its historical experience and for each period, the Company reviews the estimated forfeiture rate and makes changes as factors affecting the forfeiture rate calculations and assumptions change. In addition, the Company has issued performance-based restricted stock units that vest based upon continued service over the vesting term and achievement of certain performance goals, established by the Board of Directors, for a predetermined period. The fair value of the performance-based awards are determined based upon the closing price of the Company’s common stock on the date of the grant and the Company recognizes the fair value of awards only if it is probable the performance condition will be met. For performance-based awards, the fair value is not determined until all of the terms and conditions of the award are established.
Capitalized Software Costs	Capitalized Software Costs The Company capitalizes the costs associated with software developed or obtained for internal use, including costs incurred in connection with the development of its products, when the preliminary project stage is completed, management has decided to make the project a part of its future offering and the software will be used to perform the function intended. These capitalized costs include external direct costs of materials and services consumed in developing or obtaining internal-use software, personnel and related expenses for employees who are directly associated with and who devote time to internal-use software projects and, when material, interest costs incurred during the development. Capitalization of these costs ceases once the project is substantially complete and the software is ready for its intended purpose. Costs incurred for upgrades and enhancements to the products are also capitalized. Post-configuration training and maintenance costs are expensed as incurred. Capitalized software costs are amortized to cost of revenue using the straight-line method over an estimated useful life of the software, which is typically three years , commencing when the software is ready for its intended use. The Company does not transfer ownership of or lease its software to its clients.
Comprehensive Loss	Comprehensive Loss Comprehensive loss encompasses all changes in equity other than those arising from transactions with stockholders, and consists of net loss, currency translation adjustments and unrealized gains or losses on investments. For the years ended December 31, 2018 , 2017 and 2016 , accumulated other comprehensive income (loss) comprised a cumulative translation adjustment and also included net unrealized gains (losses) on investments.
Income Taxes	Income Taxes The Company uses the liability method of accounting for income taxes. Under the liability method, deferred taxes are determined based on the temporary differences between the financial statement and tax bases of assets and liabilities, using tax rates expected to be in effect during the years in which the bases differences are expected to reverse. A valuation allowance is recorded when it is more likely than not that some of the deferred tax assets will not be realized. In determining the need for valuation allowances, the Company considers projected future taxable income and future reversals of existing taxable differences. The Company has recorded a full valuation allowance to reduce its United States, United Kingdom, New Zealand, Hong Kong and Brazil net deferred tax assets to zero, as it has determined that it is not more likely than not that any of these net deferred tax assets will be realized. The Company has assessed its income tax positions and recorded tax benefits for all years subject to examination, based upon its evaluation of the facts, circumstances and information available at each period end. For those tax positions where the Company has determined there is a greater than 50% likelihood that a tax benefit will be sustained, the Company has recorded the largest amount of tax benefit that may potentially be realized upon ultimate settlement with a taxing authority that has full knowledge of all relevant information. For those income tax positions where it is determined there is less than 50% likelihood that a tax benefit will be sustained, no tax benefit has been recognized.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers cash and cash equivalents to include short-term, highly liquid investments that are readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value, including investments with original or remaining maturities from the date of purchase of three months or less.
Investments in Marketable Securities	Investments in Marketable Securities During the year ended December 31, 2018 the Company prospectively adopted ASU 2016-01, which requires equity securities to be measured at fair value and recognize any changes in fair value within the consolidated statements of operations. The adoption of this standard did not have a material impact on the Company’s consolidated financial statements. The cost of marketable securities sold is determined based on the specific identification method and any realized gains or losses on the sale of investments are reflected as a component of interest income or expense. In addition, the Company classifies marketable securities as current or non-current based upon the maturity dates of the securities.
Strategic Investments	Strategic Investments The Company has invested in equity securities of multiple privately-held companies. The Company accounted for each of these investment using the cost method of accounting, as the Company does not have significant influence or a controlling financial interest over these entities. These investments are subject to periodic impairment reviews and are considered to be impaired when a decline in fair value is judged to be other-than-temporary. These investments are included in long-term investments on the consolidated balance sheets, and any impairment losses are recorded in other, net in the accompanying consolidated statements of operations.
Allowance for Doubtful Accounts	Allowance for Doubtful Accounts The Company bases its allowance for doubtful accounts on its historical collection experience and a review in each period of the status of the then-outstanding accounts receivable.
Property and Equipment, Net	Property and Equipment, Net Property and equipment are recorded at historical cost, less accumulated depreciation and amortization. Depreciation is computed using the straight-line method based upon the estimated useful lives of the assets, generally two to seven years (See Note 7 ). Leasehold improvements are depreciated on a straight-line basis over the shorter of their estimated useful lives or lease terms. Repair and maintenance costs are charged to expense as incurred, while renewals and improvements are capitalized.
Impairment of Long Lived Assets	Impairment of Long Lived Assets The Company evaluates the recoverability of its long-lived assets with finite useful lives, including intangible assets, for impairment whenever events or changes in circumstances indicate that the carrying amounts may not be recoverable. Such triggering events or changes in circumstances may include: a significant decrease in the market price of a long-lived asset, a significant adverse change in the extent or manner in which a long-lived asset is being used, a significant adverse change in legal factors or in the business climate, the impact of competition or other factors that could affect the value of a long-lived asset, a significant adverse deterioration in the amount of revenue or cash flows expected to be generated from an asset group, an accumulation of costs significantly in excess of the amount originally expected for the acquisition or development of a long-lived asset, current or future operating or cash flow losses that demonstrate continuing losses associated with the use of a long-lived asset, or a current expectation that, more likely than not, a long-lived asset will be sold or otherwise disposed of significantly before the end of its previously estimated useful life. The Company performs impairment testing at the asset group level that represents the lowest level for which identifiable cash flows are largely independent of the cash flows of other assets and liabilities. If events or changes in circumstances indicate that the carrying amount of an asset group may not be recoverable and the expected undiscounted future cash flows attributable to the asset group are less than the carrying amount of the asset group, an impairment loss equal to the excess of the asset’s carrying value over its fair value is recorded. Fair value is determined based upon estimated undiscounted future cash flows.
Intangible Assets	Intangible Assets Identifiable intangible assets primarily consist of acquisition-related intangibles. The Company determines the appropriate useful life of its intangible assets by performing an analysis of expected cash flows of the acquired assets. Intangible assets are amortized over their estimated useful lives ranging from three to six years, generally using the straight-line method which approximates the pattern in which the economic benefits are consumed.
Goodwill	Goodwill Goodwill is not amortized, but instead is required to be tested for impairment annually and under certain circumstances. The Company performs such testing of goodwill in the fourth quarter of each year, or as events occur or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying amount. Events or changes in circumstances which could trigger an impairment review include a significant adverse change in legal factors or in the business climate, an adverse action or assessment by a regulator, unanticipated competition, a loss of key personnel, significant changes in the manner of the Company’s use of the acquired assets or the strategy for the Company’s overall business, significant negative industry or economic trends, or significant underperformance relative to expected historical or projected future results of operations. As part of the annual impairment test, the Company may conduct an assessment of qualitative factors to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Fair value represents the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The fair value hierarchy is based on the following three levels of inputs, of which the first two are considered observable and the last one is considered unobservable: • Level 1—Quoted prices (unadjusted) in active markets for identical assets or liabilities that management has the ability to access at the measurement date. • Level 2—Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. • Level 3—Unobservable inputs. Observable inputs are based on market data obtained from independent sources.
Concentration of Risk	Concentration of Risk Financial instruments that potentially subject the Company to concentration of credit risk consist principally of cash, cash equivalents, restricted cash and accounts receivable. The Company’s cash and cash equivalents are deposited with several financial institutions and, at times, may exceed federally insured limits, as applicable. The Company performs ongoing credit evaluations of its clients.
Foreign Currency Transactions and Translation	Foreign Currency Transactions and Translation Transactions in foreign currencies are translated into U.S. dollars at the rates of exchange in effect at the date of the transaction. Unrealized transaction (losses) gains were approximately $(0.4) million , $(3.1) million and $20 thousand for the years ended December 31, 2018 , 2017 and 2016 , respectively, and are included in other, net within other income (expense), net, in the accompanying consolidated statements of operations. The Company has entities in various countries. For entities where the local currency is different than the functional currency, the local currency financial statements have been remeasured from the local currency into the functional currency using the current exchange rate for monetary accounts and historical exchange rates for nonmonetary accounts, with exchange differences on remeasurement included in other income (loss). To the extent that the functional currency of the Company's subsidiaries is different than the U.S dollar, the financial statements have then been translated into U.S. dollars using period-end exchanges rates for assets and liabilities and average exchanges rates for the results of operations. Foreign currency translation gains and losses are included as a component of accumulated other comprehensive income or loss in the consolidated balance sheets.
Recent Accounting Pronouncements	Recently Adopted Accounting Pronouncements In June 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update No. 2018-07, "Compensation—Stock Compensation: Improvements to Nonemployee Share-Based Payment Accounting" ("ASU 2018-07"). The ASU aligns the accounting for share-based compensation for non-employees with employees. The guidance is effective for interim and annual reporting periods beginning after December 15, 2018. The Company early adopted this ASU in the second quarter of 2018, and the adoption did not have a material impact on its consolidated financial statements. In May 2017, the FASB issued Accounting Standards Update No. 2017-09, "Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting" ("ASU 2017-09"). The ASU amends the scope of modification accounting for share-based payment arrangements. It provides guidance on the types of changes to the terms or conditions of share-based payment awards to which an entity would be required to apply modification accounting under Accounting Standards Codification (“ASC”) 718, Compensation - Stock compensation . The Company implemented this requirement as of the beginning of the first quarter of 2018. The adoption did not have a material impact on its consolidated financial statements. In January 2017, the FASB issued Accounting Standards Update No. 2017-01, "Business Combinations (Topic 805) Clarifying the Definition of a Business" ("ASU 2017-01"). The ASU amended the existing FASB Accounting Standards Codification to clarify the definition of a business, which affects many areas of accounting including acquisitions, disposals, goodwill and consolidation. The Company implemented this requirement as of the beginning of the first quarter of 2018. The adoption did not have a material impact on its consolidated financial statements. In August 2016, the FASB issued FASB issued Accounting Standards Update No. 2016-15, "Classification of Certain Cash Receipts and Cash Payments" ("ASU 2016-15"). The ASU clarifies how companies present and classify certain cash receipts and cash payments in the statement of cash flows. The Company implemented this requirement as of the beginning of the first quarter of 2018. The adoption did not have a material impact on its consolidated financial statements. In January 2016, the FASB issued Accounting Standards Update No. 2016-01, "Recognition and Measurement of Financial Assets and Financial Liabilities" ("ASU 2016-01"). The ASU that provides guidance for the recognition, measurement, presentation and disclosure of financial assets and liabilities. The Company implemented this requirement as of the beginning of the first quarter of 2018. The adoption did not have a material impact on its consolidated financial statements. In May 2014, the FASB issued Accounting Standards Update No. 2014-09, "Revenue from Contracts with Customers (Topic 606)" ("ASU 2014-09"). The ASU supersedes the revenue recognition requirement in ASC Topic 605 , Revenue Recognition (“Topic 605”) , and requires the recognition of revenue to depict the transfer of promised goods or services to customers in an amount that reflects the expected consideration entitled in exchange for those goods or services. The ASU also includes Subtopic 340-40, Other Assets and Deferred Costs - Contracts with Customers , which requires the deferral of incremental costs of obtaining a contract with a customer. The Company adopted the requirements of ASU 2014-09 utilizing the modified retrospective method of transition to contracts as of January 1, 2018. The accumulated deficit balance was reduced, thus stockholders' equity was increased by $18.9 million as of January 1, 2018 due to the cumulative impact of adopting the ASU. The impact was primarily related to: • $15.5 million increase in deferred commissions. Such costs are considered to be costs to obtain a contract under Topic 606, and primarily relate to the execution of software subscription contracts. In addition, upon adoption, these incremental commission costs to obtain a contract are now amortized over a period of benefit, which is generally six years. • $2.7 million of additional liability offsets the impact to retained earnings from the increase of the deferred commission above. The liability is to accrue commission costs earned but not yet paid. • $6.1 million reduction in deferred revenue related to additional contract value being allocated to professional services delivered prior to adoption. Previously such amounts were not recognized based on contractual payment limitations. Upon adoption, revenue for professional services is based on the relative standalone selling price without any such limitation. The adoption had no impact to net cash provided by or used in operating, investing or financing activities in the Company’s consolidated statements of cash flows. Accounting Pronouncements Pending Adoption In August 2018, the FASB issued Accounting Standards Update No. 2018-15, "Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40) - Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract," ("ASU 2018-15"). The ASU aligns the accounting for implementation costs incurred in a hosting arrangement that is a service contract with the accounting for implementation costs incurred to develop or obtain internal-use software under ASC 350-40, in order to determine which costs to capitalize and recognize as an asset and which costs to expense. ASU 2018-15 is effective for annual reporting periods, and interim periods within those years, beginning after December 15, 2019, and can be applied either prospectively to implementation costs incurred after the date of adoption or retrospectively to all arrangements. The Company is currently evaluating the impact of the adoption of ASU 2018-15 on its consolidated financial statements in order to adopt the new standard in the first quarter of 2020. In February 2016, the FASB issued Accounting Standards Update No. 2016-02, "Leases (Topic 842)" ("ASU 2016-02"). The ASU requires lessees to record most leases on their balance sheets but recognize the expenses on their statements of operations in a manner similar to current accounting rules. ASU 2016-02 states that a lessee would recognize a lease liability for the obligation to make lease payments and a right-to-use (ROU) asset for the right to use the underlying asset for the lease term. The new standard is effective for interim and annual periods beginning after December 15, 2018 on a modified retrospective basis. The new standard provides a package of practical expedients for an entity’s ongoing accounting which the Company expects to elect. This means, for existing short-term leases and others that qualify, the Company will not recognize ROU assets or lease liabilities. Additionally, the Company will not separate lease and non-lease components for all of our leases. The Company is in the process of completing its assessment of the standard as the analysis of its leasing arrangements from a recent acquisition are ongoing. The Company will finalize the analysis and adopt the standard as of January 1, 2019 ("effective date") in connection with the preparation of its consolidated financial statements as of and for the quarter ended March 31, 2019. The Company expects that this standard will have a material effect on its consolidated balance sheets. The most significant impacts relate to: • the recognition of new ROU assets and operating lease liabilities on the consolidated balance sheets for its office and data center leases, with the cumulative-effect of applying the standard being recognized as a reduction to opening retained earnings as of the effective date; • the de-recognition of existing assets and liabilities for certain sale-leaseback transactions (including those arising from build-to-suit lease arrangements for which construction is complete and the Company is leasing the constructed asset) that currently do not qualify for sale accounting; and • providing significant new disclosures about the Company's leasing activities. The Company does not expect a significant change in its leasing activities as a result of the adoption.
Fair Value Measurement	Fair value represents the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Observable inputs are based on market data obtained from independent sources. The fair value hierarchy is based on the following three levels of inputs, of which the first two are considered observable and the last one is considered unobservable: • Level 1 – Quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. • Level 2 – Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. • Level 3 – Unobservable inputs.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Schedule of impact of new standard on financial statement line items	The following tables summarize the effect of the adoption of Topic 606 on the Company’s select line items, included in the consolidated condensed financial statements as of and for the year ended December 31, 2018 , as if the previous accounting was in effect (in thousands). December 31, 2018 Consolidated Condensed Balance Sheet As Reported Impacts of Adoption Without Adoption Assets Deferred commissions, current portion $ 24,467 $ 30,624 $ 55,091 Deferred commissions, non-current 45,444 (45,444 ) — Liabilities Accrued expenses 68,331 (1,697 ) 66,634 Deferred revenue, current portion 312,526 6,751 319,277 Stockholders’ Equity Accumulated deficit (529,962 ) (19,874 ) (549,836 ) Year Ended December 31, 2018 Consolidated Condensed Statement of Operations As Reported Impacts of Adoption Without Adoption Revenue $ 537,891 $ (696 ) $ 537,195 Operating expenses: Sales and marketing 224,635 (992 ) 223,643 Net loss (33,842 ) 296 (33,546 ) Net loss per share, basic and diluted (0.58 ) (0.58 ) Weighted average common shares outstanding, basic and diluted 58,159 58,159
Schedule of black-scholes option-pricing model assumptions	The following information represents the weighted average of the assumptions used in the Black-Scholes option-pricing model for stock options granted during each of the last three years: For the Years Ended December 31, 2018 2017 2016 Risk-free interest rate n/a n/a 1.4 % Expected term (in years) n/a n/a 5.8 Estimated dividend yield n/a n/a — % Estimated volatility n/a n/a 48.8 %
Reconciliation of beginning and ending amount of allowance for doubtful accounts	A reconciliation of the beginning and ending amount of allowance for doubtful accounts for the years ended December 31, 2018 , 2017 and 2016 , is as follows (in thousands): 2018 2017 2016 Beginning balance, January 1 $ 7,478 $ 3,532 $ 2,578 Additions and adjustments 1,691 7,680 3,165 Write-offs (6,740 ) (3,734 ) (2,211 ) Ending balance, December 31 $ 2,429 $ 7,478 $ 3,532

Business Acquisitions (Tables)

Business Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Allocation of total purchase consideration	The Company’s allocation of the total purchase price consideration as of September 10, 2018 is summarized below (in thousands): Fair Value Cash and cash equivalents $ 115 Other assets 68 Intangible assets - developed technology 7,500 Goodwill 10,525 Total purchase price $ 18,208 The Company’s allocation of the total purchase price consideration as of November 9, 2018 is summarized below (in thousands): Fair Value Cash and cash equivalents 508 Accounts receivable 761 Property and equipment, net 51,967 Other current and noncurrent assets 1,001 Intangible assets - content library 4,700 Intangible assets - developed technology 2,500 Goodwill 11,034 Facility financing obligation (46,100 ) Accounts payable, accrued expenses, and other liabilities, current and noncurrent (3,465 ) Net assets acquired 22,906

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Basic and diluted loss per share	The following table presents the Company's basic and diluted net loss per share (in thousands, except per share amounts): For the Years Ended December 31, 2018 * 2017 2016 Net loss $ (33,842 ) $ (61,335 ) $ (66,837 ) Weighted-average shares of common stock outstanding 58,159 57,262 55,595 Net loss per share — basic and diluted $ (0.58 ) $ (1.07 ) $ (1.20 )
Anti-dilutive shares excluded from calculation of net loss per share	At December 31, 2018 , 2017 and 2016 , the following potential shares were excluded from the computation of diluted net loss per share because their effect would have been anti-dilutive (in thousands): December 31, 2018 2017 2016 Options to purchase common stock, restricted stock units and performance-based restricted stock units 9,869 10,143 10,635 Shares issuable pursuant to employee stock purchase plan 97 114 89 Convertible notes 7,143 11,825 4,682 Common stock warrants 936 4,682 4,682 Total shares excluded from net loss per share 18,045 26,764 20,088

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Schedule of marketable securities	The following is a summary of investments in marketable securities, including those that meet the definition of a cash equivalent, as of December 31, 2018 (in thousands): December 31, 2018 Amortized Cost Basis Unrealized Gains Unrealized Losses Fair Value Cash Equivalent Investments Money market funds $ 129,321 $ — $ — $ 129,321 $ 129,321 $ — Corporate bonds 58,115 — (82 ) 58,033 — 58,033 U.S. treasury securities 138,826 — (100 ) 138,726 — 138,726 Commercial paper $ 7,973 $ — $ — $ 7,973 $ — $ 7,973 $ 334,235 $ — $ (182 ) $ 334,053 $ 129,321 $ 204,732 The following is a summary of investments in marketable securities, including those that meet the definition of a cash equivalent, as of December 31, 2017 (in thousands): December 31, 2017 Amortized Cost Basis Unrealized Gains Unrealized Losses Fair Value Cash Equivalent Investments Money market funds $ 358,859 $ — $ — $ 358,859 $ 358,859 $ — Certificate of deposits 10,000 — — 10,000 10,000 — Corporate bonds 74,868 — (220 ) 74,648 — 74,648 U.S. treasury securities 189,310 — (430 ) 188,880 — 188,880 $ 633,037 $ — $ (650 ) $ 632,387 $ 368,859 $ 263,528

Intangible Assets and Goodwill

Intangible Assets and Goodwill (Tables)	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of finite-lived intangible assets	The following table presents the gross carrying amount and accumulated amortization of finite-lived intangible assets as of December 31, 2018 and 2017 (in thousands): December 31, 2018 December 31, 2017 Gross Accumulated Net Gross Accumulated Net Developed technology $ 39,984 $ (30,817 ) $ 9,167 $ 29,984 $ (29,984 ) $ — Content library 4,700 — 4,700 — — — Total $ 44,684 $ (30,817 ) $ 13,867 $ 29,984 $ (29,984 ) $ —
Estimate of remaining amortization expense	The following table presents the Company's estimate of remaining amortization expense for finite-lived intangible assets that existed as of December 31, 2018 (in thousands): 2019 2020 2021 2022 2023 and thereafter Estimated remaining amortization expense $ 4,188 $ 4,188 $ 3,355 $ 855 $ 1,281

Other Balance Sheet Amounts (Ta

Other Balance Sheet Amounts (Tables)	12 Months Ended
	Dec. 31, 2018
Balance Sheet Related Disclosures [Abstract]
Schedule of property and equipment, net	The balance of property and equipment, net is as follows (in thousands): Useful Life December 31, 2018 2017 Computer equipment and software 3 – 5 years $ 52,055 $ 38,838 Build to suit property 25 years 51,058 — Furniture and fixtures 7 years 4,367 3,855 Leasehold improvements 2 – 6 years 9,987 10,046 Renovation in progress n/a 1,984 58 119,451 52,797 Less: accumulated depreciation and amortization (42,197 ) (31,980 ) Total property and equipment, net $ 77,254 $ 20,817
Schedule of accrued expenses	The balance of accrued expenses is as follows (in thousands): December 31, 2018 2017 Accrued compensation $ 31,799 $ 23,056 Accrued commissions 13,856 12,401 Other accrued expenses 14,051 19,071 Accrued interest $ 8,625 $ 3,000 Total accrued expenses $ 68,331 $ 57,528

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Assets and liabilities measured at fair value	Assets and liabilities measured at fair value on a recurring basis included the following as of December 31, 2018 and 2017 (in thousands): December 31, 2018 December 31, 2017 Fair Value Level 1 Level 2 Level 3 Fair Value Level 1 Level 2 Level 3 Cash equivalents $ 129,172 $ 129,172 $ — $ 368,859 $ 358,859 $ 10,000 $ — Corporate bonds 58,033 — 58,033 — 74,648 — 74,648 — U.S. treasury securities 138,726 — 138,726 — 188,880 — 188,880 — Commercial paper 7,973 — 7,973 — — — — — $ 333,904 $ 129,172 $ 204,732 $ — $ 632,387 $ 358,859 $ 273,528 $ —

Debt and Other Financing Arra_2

Debt and Other Financing Arrangements (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of the net carrying amount of debt	The net carrying amounts of the liability components of the 2018 Notes and 2021 Notes as of December 31, 2018 and 2017 consists of the following (in thousands): December 31, 2018 December 31, 2017 Principal amount $ 300,000 $ 553,000 Unamortized debt discount (4,348 ) (10,190 ) Net carrying amount before unamortized debt issuance costs 295,652 542,810 Unamortized debt issuance costs (6,685 ) (9,617 ) Net carrying value $ 288,967 $ 533,193
Schedule of note interest expense	The following table presents the interest expense recognized related to the 2018 Notes and the 2021 Notes for years ended December 31, 2018 , 2017 and 2016 (in thousands): Years Ended December 31, 2018 2017 2016 Contractual interest expense at 1.50% and 5.75% per annum $ 19,147 $ 4,897 $ 3,795 Amortization of debt issuance costs 3,086 1,472 1,263 Accretion of debt discount 5,843 8,360 7,867 Total $ 28,076 $ 14,729 $ 12,925

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Summary of stock repurchases under program	The following is a summary of the Company's stock repurchases under its $100.0 million share repurchase program as of December 31, 2018 (in thousands, except per share information): Period # of Shares Repurchased Average Price per Share Total Expenditures November 8, 2017 - December 31, 2017 635 $ 35.55 $ 22,599 January 1, 2018 - March 31, 2018 423 $ 37.84 16,024 April 1, 2018 - June 30, 2018 444 $ 46.66 20,718 July 1, 2018 - September 30, 2018 300 $ 53.82 16,143 October 1, 2018 - December 31, 2018 484 $ 50.59 24,516 Total 2,286 $ 43.71 $ 100,000

Stock-Based Awards (Tables)

Stock-Based Awards (Tables)	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of stock option activity	The following table summarizes the stock option activity which contain only service conditions, under the Company’s 1999, 2009 and 2010 Plans (in thousands, except per share and term information): Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (1) Outstanding, December 31, 2017 5,432 $ 32.73 5.3 $ 42,282 Granted — — Exercised (1,472 ) 32.48 Forfeited (132 ) 44.59 Outstanding, December 31, 2018 3,828 32.41 4.1 70,436 Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term Aggregate Intrinsic Value (1) Exercisable at December 31, 2018 3,777 $ 32.38 4.0 $ 69,658 Vested and expected to vest at December 31, 2018 3,826 32.41 4.1 70,405 (1) Based on the Company’s closing stock price of $50.43 on December 31, 2018 and $35.33 on December 31, 2017.
Schedule of stock options outstanding and exercisable	The following table summarizes information about stock options, which contain only service conditions, under the Company’s equity incentive plans at December 31, 2018 (in thousands except term information): Options Outstanding at December 31, 2018 Options Exercisable at December 31, 2018 Number of Options Weighted Average Remaining Contractual Term (in years) Number of Options Weighted Average Remaining Contractual Term (in years) Range of Exercise Prices $0.34 to $1.65 29 1.2 29 1.2 $5.93 to $8.88 618 1.9 617 1.9 $12.54 to $15.41 119 2.7 119 2.7 $16.24 to $18.82 223 3.0 223 3.0 $20.85 to $23.94 398 3.4 398 3.4 $27.55 to $31.44 129 4.7 129 4.7 $31.64 to $36.15 546 5.5 495 5.5 $38.03 to $45.76 656 4.9 656 4.9 $46.20 to $56.05 1,110 4.8 1,110 4.8 3,828 4.1 3,776 4.0
Schedule of restricted stock unit activity	Restricted stock unit activity for the year ended December 31, 2018 under the Company’s equity incentive plans is summarized as follows (shares in thousands): Number of Shares Weighted Average Grant Date Fair Value Outstanding at December 31, 2017 3,790 $ 37.22 Granted 2,227 46.17 Forfeited (530 ) 39.07 Vested (1,370 ) 36.87 Outstanding at December 31, 2018 4,117 $ 41.94
Summary of issuances of awards under new compensation award structure	The following table summarizes the Company’s issuances of awards under the new compensation award structure at December 31, 2018 : Grant Date Performance Measures Vesting Term Performance Period # of Shares at Target # of Shares at Maximum Grant Date Fair Value per share # of Shares Outstanding at Target # of Shares Outstanding at Maximum July 2016 (1) (a) the Company meeting certain revenue and cash flow targets through December 31, 2018 and (b) the recipient continuing to provide services to the Company through the end of June 2019 Three years Fiscal years 2016, 2017 and 2018 166,600 499,800 $ 38.67 — — March 2017 (a) the Company meeting certain revenue and cash flow targets through December 31, 2019 and (b) the recipient continuing to provide services to the Company through the end of March 2020 Three years Fiscal years 2017, 2018 and 2019 185,270 555,810 $ 41.73 149,490 448,470 February 2018 (a) the Company meeting certain combined subscription revenue and unlevered cash flow margin targets for the year ending December 31, 2020 and (b) the recipient continuing to provide services to the Company through the end of February 2021 Three years Fiscal year 2020 121,764 304,410 $ 40.64 121,764 304,410 February 2018 (a) the Company meeting certain combined subscription revenue and unlevered cash flow margin targets for each of the years ending December 31, 2020, December 31, 2021, and December 31, 2022 and (b) the recipient continuing to provide services to the Company through each respective vest date at the end of February 2020, 2021 and 2022 Five years (2) Fiscal years 2020, 2021 and 2022 411,412 1,028,530 $ 40.64 411,412 1,028,530 April 2018 (a) the Company meeting certain combined subscription revenue and unlevered cash flow margin targets for the year ending December 31, 2020 and (b) the recipient continuing to provide services to the Company through the beginning of April 2021 Three years Fiscal year 2020 3,572 8,930 $ 39.54 3,572 8,930 April 2018 (a) the Company meeting certain combined subscription revenue and unlevered cash flow margin targets for each of the years ending December 31, 2020, December 31, 2021, and December 31, 2022 and (b) the recipient continuing to provide services to the Company through each respective vest date at the beginning of April 2020, 2021 and 2022 Five years (2) Fiscal years 2020, 2021 and 2022 53,572 133,930 $ 39.54 53,572 133,930 (1) In December 2018, based on the performance of the Company’s results for certain revenue and cash flow targets, the Company determined it had not achieved the required performance level for the performance-based awards granted in July 2016, which resulted in none of the shares being issued. (2) One-third of the total eligible shares shall vest on each of the third, fourth and fifth anniversaries of the grant date. This award is a one-time equity award intended to cover expected grant levels over a three-year period. In exchange, the Compensation Committee does not plan to grant any additional equity awards to recipients of this award until 2021.
Summary of stock-based compensation expense	Stock-based compensation expense related to stock options, restricted stock units, the ESPP and performance-based restricted stock units is included in the following line items in the accompanying consolidated statements of operations for the years ended December 31, 2018 , 2017 and 2016 (in thousands): Years Ended December 31, 2018 2017 2016 Cost of revenue $ 4,218 $ 4,904 $ 4,732 Sales and marketing 24,440 28,427 25,642 Research and development 11,800 9,630 7,586 General and administrative 19,872 22,869 16,739 Restructuring 6,227 — — Total $ 66,557 $ 65,830 $ 54,699

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Summary of income before income tax, domestic and foreign	The components of the Company’s loss before provision (benefit) for income taxes are as follows (in thousands): Years Ended December 31, 2018 * 2017 2016 United States $ (21,174 ) $ (32,853 ) $ (39,107 ) Foreign (10,073 ) (26,736 ) (26,523 ) Loss before provision for income taxes $ (31,247 ) $ (59,589 ) $ (65,630 ) * See Note 2 for summary of adjustments in relation to the adoption of ASC 606.
Components of income tax provision (benefit)	The components of the provision (benefit) for income taxes attributable to continuing operations are as follows (in thousands): Years Ended December 31, 2018 2017 2016 Current income tax provision: Federal $ — $ — $ — State 204 114 105 Foreign 2,514 1,580 1,838 Total current income tax provision 2,718 1,694 1,943 Deferred income tax benefit: Federal — — — State — — — Foreign (123 ) 52 (736 ) Total deferred income tax benefit (123 ) 52 (736 ) Total income tax provision (benefit) $ 2,595 $ 1,746 $ 1,207
Schedule of effective income tax rate reconciliation	The differences in the total provision for income taxes that would result from applying the 21% federal statutory rate beginning in 2018 and 34% federal statutory rate prior to 2018 to loss before provision for income taxes and the reported provision for income taxes are as follows (in thousands): Years Ended December 31, 2018 2017 2016 U.S. Federal tax benefit at statutory rates $ (6,562 ) $ (20,260 ) $ (22,310 ) State income taxes, net of federal tax benefit (248 ) (806 ) (855 ) Foreign rate differential 2,764 5,220 3,711 Stock based compensation 3,029 3,182 4,467 Other permanent differences 280 (494 ) (750 ) Deferred adjustments / U.S. rate change 1,430 7,811 — Other 130 262 1,494 Valuation allowance 1,772 6,831 15,450 Total income tax (benefit) provision $ 2,595 $ 1,746 $ 1,207
Schedule of the components of deferred tax assets and liabilities	Major components of the Company’s deferred tax assets (liabilities) at December 31, 2018 and 2017 are as follows (in thousands): December 31, 2018 2017 Deferred tax assets: Accrued expenses $ 2,353 $ 2,371 Long-lived intangible assets and fixed assets — basis difference 22,947 19,884 Net operating loss carryforwards 82,017 80,615 Stock-based compensation 15,172 16,886 Deferred revenue 2,861 2,739 Convertible note hedge — 1,467 Other 4,557 2,721 Total deferred tax assets 129,907 126,683 Valuation allowance (117,058 ) (118,606 ) Deferred tax assets, net of valuation allowance 12,849 8,077 Deferred tax liabilities: Prepaid expenses and deferred commissions (10,831 ) (5,672 ) Convertible note discount — (1,074 ) Other (976 ) (410 ) Total deferred tax liabilities (11,807 ) (7,156 ) Net deferred tax assets (liabilities) $ 1,042 $ 921
Summary of the reconciliation of unrecognized tax benefits	A reconciliation of the beginning and ending amount of unrecognized tax benefits for the years ended December 31, 2018 , 2017 and 2016 is as follows (in thousands): Years Ended December 31, 2018 2017 2016 Balance at January 1 $ 1,271 $ 276 $ 276 Additions for tax positions related to the current year 131 995 — Balance at December 31 $ 1,402 $ 1,271 $ 276

Segment and Geographic Inform_2

Segment and Geographic Information (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Schedule of revenue by source	The following table sets forth the Company’s sources of revenue (dollars in thousands): At or For Year Ended December 31, 2018 * 2017 2016 Subscription revenue $ 473,052 $ 396,764 $ 339,756 Percentage of subscription revenue to total revenue 87.9 % 82.3 % 80.3 % Professional services revenue $ 64,839 $ 85,221 $ 83,368 Percentage of professional services revenue to total revenue 12.1 % 17.7 % 19.7 % $ 537,891 $ 481,985 $ 423,124 * See Note 2 for summary of adjustments in relation to the adoption of ASC 606.
Schedule of revenue from external customers and long-lived assets, by geographical areas	Revenue by geographic region, which is generally based on the address of the Company’s clients as defined in their master subscription agreements, is set forth below (in thousands): Years Ended December 31, 2018 * 2017 2016 Revenue United States $ 343,205 $ 313,729 $ 284,657 All other countries 194,686 168,256 138,467 Total revenue $ 537,891 $ 481,985 $ 423,124 * See Note 2 for summary of adjustments in relation to the adoption of ASC 606. Property and equipment by region is set forth below (in thousands): December 31, 2018 2017 Property and equipment, net United States $ 69,550 $ 16,468 United Kingdom 3,558 3,378 All other countries 4,146 971 Total property and equipment, net $ 77,254 $ 20,817

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of future minimum lease payments	Future minimum lease payments under non-cancelable operating leases at December 31, 2018 are as follows (in thousands): Operating Leases (1) 2019 $ 11,576 2020 14,162 2021 14,277 2022 14,823 2023 14,710 Thereafter 17,961 Total minimum lease payments $ 87,509 (1) The table above includes future minimum lease payments for the Company's facility financing obligation as follows: 2019: $4.8 million ; 2020: $4.9 million ; 2021: $4.9 million ; 2022: $5.3 million ; 2023 and thereafter: $21.7 million .

Selected Quarterly Data (Unau_2

Selected Quarterly Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Schedule of quarterly consolidated statements of operations	The following unaudited quarterly consolidated statements of operations for each of the quarters in the years ended December 31, 2018 and 2017 have been prepared on a basis consistent with the Company’s audited annual consolidated financial statements and include, in the opinion of management, all normal recurring adjustments necessary for the fair presentation of the financial information contained in these statements. Quarter Ended (in thousands, except per share data) Mar. 31, June 30, Sept. 30, Dec. 31, Mar. 31, June 30, Sept. 30, Dec. 31, Revenue $ 111,582 $ 116,651 $ 121,796 $ 131,956 $ 133,113 $ 132,517 $ 134,014 $ 138,247 Cost of revenue 33,949 35,321 35,708 37,889 37,020 36,365 36,171 34,793 Gross profit 77,633 81,330 86,088 94,067 96,093 96,152 97,843 103,454 Operating expenses: Sales and marketing 56,894 62,073 60,554 60,750 59,245 59,821 53,215 52,354 Research and development 13,411 14,684 16,389 17,491 15,984 16,325 19,705 24,967 General and administrative 20,476 23,141 21,249 19,723 21,985 22,101 23,128 23,535 Restructuring — — — 1,539 7,725 1,000 221 — Total operating expenses 90,781 99,898 98,192 99,503 104,939 99,247 96,269 100,856 (Loss) income from operations (13,148 ) (18,568 ) (12,104 ) (5,436 ) (8,846 ) (3,095 ) 1,574 2,598 (Loss) income from operations per share, basic and diluted $ (0.23 ) $ (0.33 ) $ (0.21 ) $ (0.09 ) $ (0.15 ) $ (0.05 ) $ 0.03 $ 0.04 Other income (expense): Interest income (expense) and other income (expense), net (2,492 ) (2,333 ) (2,248 ) (3,260 ) (6,837 ) (8,376 ) (3,499 ) (4,767 ) Loss before income tax provision (15,640 ) (20,901 ) (14,352 ) (8,696 ) (15,683 ) (11,471 ) (1,925 ) (2,169 ) Income tax provision (571 ) (364 ) (503 ) (308 ) (533 ) (536 ) (522 ) (1,004 ) Net loss $ (16,211 ) $ (21,265 ) $ (14,855 ) $ (9,004 ) $ (16,216 ) $ (12,007 ) $ (2,447 ) $ (3,173 ) Net loss per share, basic and diluted $ (0.29 ) $ (0.37 ) $ (0.26 ) $ (0.16 ) $ (0.28 ) $ (0.21 ) $ (0.04 ) $ (0.05 ) Weighted average common shares outstanding, basic and diluted 56,642 56,935 57,627 57,826 57,425 57,844 58,699 58,649 * See Note 2 for summary of adjustments in relation to the adoption of ASC 606.

Organization (Details)

Organization (Details)	12 Months Ended
	Dec. 31, 2018segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating segments	1

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Revenue Recognition, Deferred Revenue and Transaction Price Allocation (Details) - USD ($) $ in Millions	Jan. 01, 2018	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Expected to be recognized from remaining performance obligations		$ 876
Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Revenue recognized	$ 301.6

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Revenue Recognition, Sales Commission (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Commissions deferred during the period	$ 65.3	$ 48.2	$ 33.3
Deferred commissions	$ 69.9	42.8
Minimum
Disaggregation of Revenue [Line Items]
Commission payment period	45 days
Maximum
Disaggregation of Revenue [Line Items]
Commission payment period	75 days
Sales and marketing
Disaggregation of Revenue [Line Items]
Commissions expense	$ 37.9	$ 41.7	$ 33

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Revenue Recognition, Impact on Financial Statements (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets
Deferred commissions, current portion	$ 24,467				$ 42,806				$ 24,467	$ 42,806
Deferred commissions, non-current	45,444				0				45,444	0
Liabilities
Accrued expenses	68,331				57,528				68,331	57,528
Deferred revenue, current portion	312,526				311,997				312,526	311,997
Stockholders’ Equity
Accumulated deficit	(529,962)				(515,054)				(529,962)	(515,054)
Revenue	138,247	$ 134,014	$ 132,517	$ 133,113	131,956	$ 121,796	$ 116,651	$ 111,582	537,891	481,985	$ 423,124
Operating expenses:
Sales and marketing	52,354	53,215	59,821	59,245	60,750	60,554	62,073	56,894	224,635	240,271	225,781
Net loss	$ (3,173)	$ (2,447)	$ (12,007)	$ (16,216)	$ (9,004)	$ (14,855)	$ (21,265)	$ (16,211)	$ (33,842)	$ (61,335)	$ (66,837)
Net loss per share — basic and diluted (usd per share)	$ (0.05)	$ (0.04)	$ (0.21)	$ (0.28)	$ (0.16)	$ (0.26)	$ (0.37)	$ (0.29)	$ (0.58)	$ (1.07)	$ (1.20)
Weighted average common shares outstanding, basic and diluted (in shares)	58,649	58,699	57,844	57,425	57,826	57,627	56,935	56,642	58,159	57,262	55,595
Impacts of Adoption | Accounting Standards Update 2014-09
Assets
Deferred commissions, current portion	$ 30,624								$ 30,624
Deferred commissions, non-current	(45,444)								(45,444)
Liabilities
Accrued expenses	(1,697)								(1,697)
Deferred revenue, current portion	6,751								6,751
Stockholders’ Equity
Accumulated deficit	(19,874)								(19,874)
Revenue									(696)
Operating expenses:
Sales and marketing									(992)
Net loss									296
Without Adoption (ASC 605)
Assets
Deferred commissions, current portion	55,091								55,091
Deferred commissions, non-current	0								0
Liabilities
Accrued expenses	66,634								66,634
Deferred revenue, current portion	319,277								319,277
Stockholders’ Equity
Accumulated deficit	$ (549,836)								(549,836)
Revenue									537,195
Operating expenses:
Sales and marketing									223,643
Net loss									$ (33,546)
Net loss per share — basic and diluted (usd per share)									$ (0.58)
Weighted average common shares outstanding, basic and diluted (in shares)									58,159

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Advertising (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Advertising expense	$ 7.1	$ 9	$ 6.6

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Share-Based Compensation (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock Based Compensation - Black-Scholes Option-Pricing Model Assumptions:
Tax benefit from share based compensation	$ 0	$ 0	$ 0
Stock options
Stock Based Compensation - Black-Scholes Option-Pricing Model Assumptions:
Risk-free interest rate			1.40%
Expected term (in years)			5 years 9 months 18 days
Estimated dividend yield			0.00%
Estimated volatility			48.80%

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - Capitalized Software Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Capitalized Software Costs
Capitalized software costs, estimated useful life	3 years
Capitalized software costs, amount capitalized during the period	$ 31.6	$ 24.3	$ 20.9
Amortization of capitalized software costs	23.5	$ 17.6	$ 13.2
Capitalized software costs, estimated amortization expense within the next year	22.3
Capitalized software costs, estimated amortization expense within two years	13.5
Capitalized software costs, estimated amortization expense within three years	4.6
Capitalized software costs, estimated amortization expense within four years	$ 0.1

Summary of Significant Accou_10

Summary of Significant Accounting Policies - Cash, Investments, and Restricted Cash (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Cash and Cash Equivalents
Cash balances	$ 54.4	$ 24.7
Money market funds backed by U.S. Treasury Securities	129.2	358.9
Certificates of deposit	0	10
Investments in Marketable Securities
Marketable Securities	$ 204.7	$ 263.5

Summary of Significant Accou_11

Summary of Significant Accounting Policies - Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for Doubtful Accounts - Reconciliation:
Accounts receivable allowance, Beginning balance	$ 7,478	$ 3,532	$ 2,578
Additions and adjustments	1,691	7,680	3,165
Write-offs	(6,740)	(3,734)	(2,211)
Accounts receivable allowance, Ending balance	2,429	7,478	3,532
Bad debt expense recognized	$ 800	$ 1,400	$ 800

Summary of Significant Accou_12

Summary of Significant Accounting Policies - Property and Equipment, Net (Details)	12 Months Ended
	Dec. 31, 2018
Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	2 years
Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	7 years

Summary of Significant Accou_13

Summary of Significant Accounting Policies - Impairment, Intangible Assets, and Goodwill (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Impairment charges related to identified intangible assets	$ 0	$ 1,300,000
Intangible Assets
Goodwill, impairment loss	$ 0	$ 0
Minimum
Intangible Assets
Identified intangible assets amortization period	3 years
Maximum
Intangible Assets
Identified intangible assets amortization period	6 years

Summary of Significant Accou_14

Summary of Significant Accounting Policies - Convertible Notes (Details) - Convertible notes - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2013	Jun. 30, 2013
The 2018 Notes
Debt Instrument [Line Items]
Interest rate on convertible notes issued	1.50%		1.50%	1.50%
Debt issued, senior convertible notes			$ 253,000,000	$ 253,000,000
The 2021 Notes
Debt Instrument [Line Items]
Interest rate on convertible notes issued	5.75%	5.75%
Debt issued, senior convertible notes		$ 300,000,000

Summary of Significant Accou_15

Summary of Significant Accounting Policies - Foreign Currency Transactions and Translation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other income (expense), net
Foreign Currency Fair Value Hedge Derivative [Line Items]
Foreign currency transactions and translation	$ (400)	$ (3,100)	$ 20

Summary of Significant Accou_16

Summary of Significant Accounting Policies - Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	Jan. 01, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in stockholders' equity		$ 55,907	$ 22,120	$ 26,963	$ 7,822
Commissions deferred during the period		65,300	48,200	$ 33,300
Accrued commissions		$ 13,856	$ 12,401
Impacts of Adoption | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in stockholders' equity	$ 18,900
Commissions deferred during the period	15,500
Accrued commissions	2,700
Reduction in deferred revenue	$ 6,100

Business Acquisitions - Additio

Business Acquisitions - Additional Information (Details) - USD ($) $ in Thousands	Nov. 09, 2018	Sep. 10, 2018	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Facility financing obligation			$ 46,100	$ 0
Workpop Inc.
Business Acquisition [Line Items]
Cash consideration paid		$ 18,200
Cost basis investment		500
Acquisition related costs		$ 500
Grovo Learning, Inc.
Business Acquisition [Line Items]
Cash consideration paid	$ 22,900
Acquisition related costs	600
Facility financing obligation	$ 46,100
Property and equipment, useful life	25 years
Content library | Grovo Learning, Inc.
Business Acquisition [Line Items]
Identified intangible assets amortization period	6 years
Developed technology | Workpop Inc.
Business Acquisition [Line Items]
Identified intangible assets amortization period		3 years
Developed technology | Grovo Learning, Inc.
Business Acquisition [Line Items]
Identified intangible assets amortization period	3 years
Build to suit property
Business Acquisition [Line Items]
Property and equipment, useful life			25 years
Build to suit property | Grovo Learning, Inc.
Business Acquisition [Line Items]
Build-to-suit property capitalized	$ 51,100

Business Acquisitions - Allocat

Business Acquisitions - Allocation of Total Purchase Consideration (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Nov. 09, 2018	Sep. 10, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill	$ 47,453			$ 25,894
Workpop Inc.
Business Acquisition [Line Items]
Cash and cash equivalents			$ 115
Other current and noncurrent assets			68
Intangible assets - content library and developed technology			7,500
Goodwill			10,525
Total purchase price			$ 18,208
Grovo Learning, Inc.
Business Acquisition [Line Items]
Cash and cash equivalents		$ 508
Accounts receivable		761
Property and equipment, net		51,967
Other current and noncurrent assets		1,001
Goodwill		11,034
Facility financing obligation		(46,100)
Accounts payable, accrued expenses, and other liabilities, current and noncurrent		(3,465)
Total purchase price		22,906
Content library | Grovo Learning, Inc.
Business Acquisition [Line Items]
Intangible assets - content library and developed technology		4,700
Developed technology | Grovo Learning, Inc.
Business Acquisition [Line Items]
Intangible assets - content library and developed technology		$ 2,500

Net Loss Per Share - Basic and

Net Loss Per Share - Basic and Diluted Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net loss									$ (33,842)	$ (61,335)	$ (66,837)
Weighted-average shares of common stock outstanding (in shares)	58,649	58,699	57,844	57,425	57,826	57,627	56,935	56,642	58,159	57,262	55,595
Net loss per share — basic and diluted (usd per share)	$ (0.05)	$ (0.04)	$ (0.21)	$ (0.28)	$ (0.16)	$ (0.26)	$ (0.37)	$ (0.29)	$ (0.58)	$ (1.07)	$ (1.20)

Net Loss Per Share - Anti-dilut

Net Loss Per Share - Anti-dilutive Shares Excluded From Calculation of Net Loss Per Share (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from net loss per share (in shares)	18,045	26,764	20,088
Options to purchase common stock, restricted stock units and performance-based restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from net loss per share (in shares)	9,869	10,143	10,635
Shares issuable pursuant to employee stock purchase plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from net loss per share (in shares)	97	114	89
Convertible notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from net loss per share (in shares)	7,143	11,825	4,682
Common stock warrants | Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from net loss per share (in shares)	936	4,682	4,682

Investments (Details)

Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	$ 334,235	$ 633,037
Unrealized Gains	0	0
Unrealized Losses	(182)	(650)
Fair Value	$ 334,053	632,387
Investments, weighted average maturity	2 months
Money market funds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	$ 129,321	358,859
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	129,321	358,859
Certificate of deposits
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis		10,000
Unrealized Gains		0
Unrealized Losses		0
Fair Value		10,000
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	58,115	74,868
Unrealized Gains	0	0
Unrealized Losses	(82)	(220)
Fair Value	58,033	74,648
U.S. treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	138,826	189,310
Unrealized Gains	0	0
Unrealized Losses	(100)	(430)
Fair Value	138,726	188,880
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	7,973
Unrealized Gains	0
Unrealized Losses	0
Fair Value	7,973
Cash Equivalent
Debt Securities, Available-for-sale [Line Items]
Fair Value	129,321	368,859
Cash Equivalent | Money market funds
Debt Securities, Available-for-sale [Line Items]
Fair Value	129,321	358,859
Cash Equivalent | Certificate of deposits
Debt Securities, Available-for-sale [Line Items]
Fair Value		10,000
Cash Equivalent | Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Fair Value	0	0
Cash Equivalent | U.S. treasury securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	0	0
Cash Equivalent | Commercial paper
Debt Securities, Available-for-sale [Line Items]
Fair Value	0
Investments
Debt Securities, Available-for-sale [Line Items]
Fair Value	204,732	263,528
Investments | Money market funds
Debt Securities, Available-for-sale [Line Items]
Fair Value	0	0
Investments | Certificate of deposits
Debt Securities, Available-for-sale [Line Items]
Fair Value		0
Investments | Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Fair Value	58,033	74,648
Investments | U.S. treasury securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	138,726	$ 188,880
Investments | Commercial paper
Debt Securities, Available-for-sale [Line Items]
Fair Value	$ 7,973

Intangible Assets and Goodwil_2

Intangible Assets and Goodwill - Schedule of Finite-lived Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 44,684	$ 29,984
Accumulated Amortization	(30,817)	(29,984)
Net Carrying Amount	13,867	0
Developed technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	39,984	29,984
Accumulated Amortization	(30,817)	(29,984)
Net Carrying Amount	9,167	0
Content library
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	4,700	0
Accumulated Amortization	0	0
Net Carrying Amount	$ 4,700	$ 0

Intangible Assets and Goodwil_3

Intangible Assets and Goodwill - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Nov. 09, 2018	Sep. 10, 2018
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 800,000	$ 7,400,000	$ 9,300,000
Impairment charges	0	0	$ 0
Goodwill	47,453,000	25,894,000
Goodwill additions	20,800,000
Goodwill, impairment loss	0	$ 0
Workpop Inc.
Finite-Lived Intangible Assets [Line Items]
Goodwill					$ 10,525,000
Workpop Inc. | Developed technology
Finite-Lived Intangible Assets [Line Items]
Additional finite-lived intangible assets	7,500,000
Grovo Learning, Inc.
Finite-Lived Intangible Assets [Line Items]
Goodwill				$ 11,034,000
Grovo Learning, Inc. | Developed technology
Finite-Lived Intangible Assets [Line Items]
Additional finite-lived intangible assets	$ 7,200,000

Intangible Assets and Goodwil_4

Intangible Assets and Goodwill - Estimated Remaining Amortization (Details) $ in Thousands	Dec. 31, 2018USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
Estimated remaining amortization expense, 2019	$ 4,188
Estimated remaining amortization expense, 2020	4,188
Estimated remaining amortization expense, 2021	3,355
Estimated remaining amortization expense, 2022	855
Estimated remaining amortization expense, 2023 and thereafter	$ 1,281

Other Balance Sheet Amounts - P

Other Balance Sheet Amounts - Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 119,451	$ 52,797
Less: accumulated depreciation and amortization	(42,197)	(31,980)
Total property and equipment, net	77,254	20,817
Depreciation expense	$ 10,200	10,300	$ 9,900
Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	2 years
Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	7 years
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 52,055	38,838
Computer equipment and software | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Computer equipment and software | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years
Build to suit property
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 51,058	0
Property and equipment, useful life	25 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 4,367	3,855
Property and equipment, useful life	7 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 9,987	10,046
Leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	2 years
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	6 years
Renovation in progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,984	$ 58

Other Balance Sheet Amounts - A

Other Balance Sheet Amounts - Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Accrued compensation	$ 31,799	$ 23,056
Accrued commissions	13,856	12,401
Other accrued expenses	14,051	19,071
Accrued interest	8,625	3,000
Total accrued expenses	$ 68,331	$ 57,528

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	$ 334,053	$ 632,387
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	58,033	74,648
U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	138,726	188,880
Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	129,172	368,859
Assets and liabilities measured at fair value, total	333,904	632,387
Recurring basis | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	129,172	358,859
Assets and liabilities measured at fair value, total	129,172	358,859
Recurring basis | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		10,000
Assets and liabilities measured at fair value, total	204,732	273,528
Recurring basis | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Assets and liabilities measured at fair value, total	0	0
Recurring basis | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	58,033	74,648
Recurring basis | Corporate bonds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Recurring basis | Corporate bonds | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	58,033	74,648
Recurring basis | Corporate bonds | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Recurring basis | U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	138,726	188,880
Recurring basis | U.S. treasury securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Recurring basis | U.S. treasury securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	138,726	188,880
Recurring basis | U.S. treasury securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Recurring basis | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	7,973	0
Recurring basis | Commercial paper | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Recurring basis | Commercial paper | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	7,973	0
Recurring basis | Commercial paper | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	$ 0	$ 0

Fair Value of Financial Instr_4

Fair Value of Financial Instruments - Additional Information (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 129,172	$ 368,859
Recurring basis | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	129,172	$ 358,859
The 2021 Notes | Convertible Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of convertible notes	$ 415,000

Debt and Other Financing Arra_3

Debt and Other Financing Arrangements - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2013	Dec. 31, 2018	Jul. 01, 2018	Jun. 30, 2013
Debt Instrument [Line Items]
Payments of debt issuance costs and proceeds from convertible notes		$ 285,077,000	$ 0
Proceeds from the issuance of warrants				$ 23,200,000
Number of shares purchasable upon warrant exercise (in shares)				4,700,000
Warrants exercise price (usd per share)				$ 80.06
Warrants expired (in shares)					3,700,000
Warrants outstanding (in shares)					900,000
Convertible Debt
Debt Instrument [Line Items]
Unamortized debt issuance costs	$ 9,617,000	9,617,000			$ 6,685,000
Unamortized debt discount	(10,190,000)	(10,190,000)			$ (4,348,000)
The 2018 Notes | Convertible Debt
Debt Instrument [Line Items]
Debt issued, senior convertible notes				$ 253,000,000			$ 253,000,000
Interest rate on convertible notes issued				1.50%	1.50%		1.50%
Principal amount repaid						$ 253,000,000
Debt recorded				$ 214,300,000
Adjustments for equity component of convertible debt				(38,700,000)
Unamortized debt issuance costs				7,300,000
Unamortized debt issuance expense				6,200,000
Issuance cost allocated to equity components				$ 1,100,000
Conversion price on convertible debt (usd per share)				$ 54.04
Payments of debt issuance costs and proceeds from convertible notes				$ 245,700,000
Payments for convertible note hedges				$ (49,500,000)
Note hedges on common stock (in shares)				4,700,000
The 2021 Notes | Convertible Debt
Debt Instrument [Line Items]
Debt issued, senior convertible notes	$ 300,000,000	$ 300,000,000
Interest rate on convertible notes issued	5.75%	5.75%			5.75%
Unamortized debt issuance costs	$ 9,200,000	$ 9,200,000
Debt issuance price, percentage	98.00%
Proceeds from issuance of debt	$ 294,000,000
Conversion rate on convertible debt	23.8095
Conversion price on convertible debt (usd per share)	$ 42	$ 42
Debt repurchase price, percentage	100.00%
Debt issuance discount	2.00%
Unamortized debt discount	$ (6,000,000)	$ (6,000,000)
Effective interest rate					6.40%
Payments of debt issuance costs and proceeds from convertible notes	$ 284,900,000

Debt and Other Financing Arra_4

Debt and Other Financing Arrangements - Summary of the Net Carrying Amount of Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Net carrying value	$ 288,967	$ 285,168
Convertible Debt
Debt Instrument [Line Items]
Principal amount	300,000	553,000
Unamortized debt discount	(4,348)	(10,190)
Net carrying amount before unamortized debt issuance costs	295,652	542,810
Unamortized debt issuance costs	(6,685)	(9,617)
Net carrying value	$ 288,967	$ 533,193

Debt and Other Financing Arra_5

Debt and Other Financing Arrangements - Schedule of Note Interest Expense (Details) - Convertible Debt - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2013	Jun. 30, 2013
Debt Instrument [Line Items]
Contractual interest expense at 1.50% and 5.75% per annum	$ 19,147	$ 4,897	$ 3,795
Amortization of debt issuance costs	3,086	1,472	1,263
Accretion of debt discount	5,843	8,360	7,867
Total	$ 28,076	$ 14,729	$ 12,925
The 2018 Notes
Debt Instrument [Line Items]
Interest rate on convertible notes issued	1.50%			1.50%	1.50%
The 2021 Notes
Debt Instrument [Line Items]
Interest rate on convertible notes issued	5.75%	5.75%

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($)	2 Months Ended	3 Months Ended				12 Months Ended		14 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Nov. 30, 2017
Equity [Abstract]
Common stock authorized (in shares)	1,000,000,000	1,000,000,000				1,000,000,000	1,000,000,000	1,000,000,000
Common stock par value (usd per share)	$ 0.0001	$ 0.0001				$ 0.0001	$ 0.0001	$ 0.0001
Preferred stock authorized (in shares)		50,000,000				50,000,000		50,000,000
Preferred stock, par value (usd per share)		$ 0.0001				$ 0.0001		$ 0.0001
Preferred stock issued (in shares)	0	0				0	0	0
Preferred stock outstanding (in shares)	0	0				0	0	0
Share repurchase program, shares authorized to repurchase									$ 100,000,000
Common stock repurchased (in shares)	635,000	484,000	300,000	444,000	423,000	1,651,000	635,000	2,286,000
Average repurchase price (usd per share)	$ 35.55	$ 50.59	$ 53.82	$ 46.66	$ 37.84	$ 46.85		$ 43.71
Value of shares repurchased	$ 22,599,000	$ 24,516,000	$ 16,143,000	$ 20,718,000	$ 16,024,000	$ 77,401,000	$ 22,599,000	$ 100,000,000

Stockholders' Equity - Repurcha

Stockholders' Equity - Repurchases under Program (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	2 Months Ended	3 Months Ended				12 Months Ended		14 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018
Equity [Abstract]
Number of Shares Repurchased (in shares)	635	484	300	444	423	1,651	635	2,286
Average Price per Share (usd per share)	$ 35.55	$ 50.59	$ 53.82	$ 46.66	$ 37.84	$ 46.85		$ 43.71
Total Expenditures	$ 22,599	$ 24,516	$ 16,143	$ 20,718	$ 16,024	$ 77,401	$ 22,599	$ 100,000

Stock-Based Awards - Plans Info

Stock-Based Awards - Plans Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of the fair market value at time of grant	85.00%
Percentage of the fair market value at the time of exercise	85.00%
Compensation expense recognized	$ 66,557	$ 65,830	$ 54,699
Incentive stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense recognized	$ 4,800	14,000	23,000
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (in shares)	2,227,000
Compensation expense recognized	$ 53,200	44,100	31,900
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issuable under plan (in shares)	3,438,935
Compensation expense recognized	$ 1,900	$ 1,600	$ 1,400
1999 and 2009 Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issuable under plan (in shares)	0
2010 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issuable under plan (in shares)	4,145,181
Additional issuable shares authorization, annual increase, maximum number of shares (in shares)	5,500,000
Additional issuable shares authorization, annual increase, percentage of outstanding stock, maximum	4.50%
2010 Plan | Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (in shares)	2,227,182
2010 Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized under plan (in shares)	3,680,480
2010 Plan | Minimum | Incentive stock options | Individual owning more than 10% of outstanding stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price as percentage of fair market value per share	110.00%
2010 Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares to be added from 1999 and 2009 Plans (in shares)	5,614,369
2010 Plan | Maximum | Incentive stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award expiration period	10 years
2010 Plan | Maximum | Incentive stock options | Individual owning more than 10% of outstanding stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award expiration period	5 years

Stock-Based Awards - Summary of

Stock-Based Awards - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Stock Options Outstanding, Shares
Shares outstanding, beginning of period (in shares)	5,432
Granted (in shares)	0
Exercised (in shares)	(1,472)
Forfeited (in shares)	(132)
Shares outstanding, period end (in shares)	3,828	5,432
Stock Options Outstanding, Weighted Average Exercise Price
Weighted average exercise price, outstanding, beginning of period (in usd per share)	$ 32.73
Weighted average exercise price, granted (in usd per share)	0
Weighted average exercise price, exercised (in usd per share)	32.48
Weighted average exercise price, forfeited (in usd per share)	44.59
Weighted average exercise price, outstanding, period end (in usd per share)	$ 32.41	$ 32.73
Stock Options, Additional Disclosures
Weighted average remaining contractual term, outstanding	4 years 1 month 6 days	5 years 4 months 5 days
Aggregate intrinsic value, outstanding	$ 70,436	$ 42,282
Exercisable (in shares)	3,777
Weighted average exercise price, exercisable (in usd per share)	$ 32.38
Weighted average remaining contractual term, exercisable	4 years
Aggregate intrinsic value, exercisable	$ 69,658
Stock Options Vested and Expected to Vest
Shares vested and expected to vest (in shares)	3,826
Weighted average exercise price, vested and expected (in usd per share)	$ 32.41
Weighted average remaining contractual term, vested and expected to vest	4 years 1 month 6 days
Aggregate intrinsic value, vested and expected to vest	$ 70,405
Closing stock price (usd per share)	$ 50.43	$ 35.33

Stock-Based Awards - Schedule o

Stock-Based Awards - Schedule of Stock Options Outstanding and Exercisable (Details) shares in Thousands	12 Months Ended
	Dec. 31, 2018$ / sharesshares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, number of options (in shares)	3,828
Options outstanding, weighted average remaining contractual life	4 years 1 month 6 days
Options exercisable, number of options (in shares)	3,776
Options exercisable, weighted average remaining contractual life	4 years
$0.34 to $1.65
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower (in usd per share) | $ / shares	$ 0.34
Range of exercise prices, upper (in usd per share) | $ / shares	$ 1.65
Options outstanding, number of options (in shares)	29
Options outstanding, weighted average remaining contractual life	1 year 2 months 12 days
Options exercisable, number of options (in shares)	29
Options exercisable, weighted average remaining contractual life	1 year 2 months 12 days
$5.93 to $8.88
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower (in usd per share) | $ / shares	$ 5.93
Range of exercise prices, upper (in usd per share) | $ / shares	$ 8.88
Options outstanding, number of options (in shares)	618
Options outstanding, weighted average remaining contractual life	1 year 10 months 24 days
Options exercisable, number of options (in shares)	617
Options exercisable, weighted average remaining contractual life	1 year 10 months 24 days
$12.54 to $15.41
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower (in usd per share) | $ / shares	$ 12.54
Range of exercise prices, upper (in usd per share) | $ / shares	$ 15.41
Options outstanding, number of options (in shares)	119
Options outstanding, weighted average remaining contractual life	2 years 8 months 12 days
Options exercisable, number of options (in shares)	119
Options exercisable, weighted average remaining contractual life	2 years 8 months 12 days
$16.24 to $18.82
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower (in usd per share) | $ / shares	$ 16.24
Range of exercise prices, upper (in usd per share) | $ / shares	$ 18.82
Options outstanding, number of options (in shares)	223
Options outstanding, weighted average remaining contractual life	3 years
Options exercisable, number of options (in shares)	223
Options exercisable, weighted average remaining contractual life	3 years
$20.85 to $23.94
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower (in usd per share) | $ / shares	$ 20.85
Range of exercise prices, upper (in usd per share) | $ / shares	$ 23.94
Options outstanding, number of options (in shares)	398
Options outstanding, weighted average remaining contractual life	3 years 4 months 24 days
Options exercisable, number of options (in shares)	398
Options exercisable, weighted average remaining contractual life	3 years 4 months 24 days
$27.55 to $31.44
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower (in usd per share) | $ / shares	$ 27.55
Range of exercise prices, upper (in usd per share) | $ / shares	$ 31.44
Options outstanding, number of options (in shares)	129
Options outstanding, weighted average remaining contractual life	4 years 8 months 12 days
Options exercisable, number of options (in shares)	129
Options exercisable, weighted average remaining contractual life	4 years 8 months 12 days
$31.64 to $36.15
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower (in usd per share) | $ / shares	$ 31.64
Range of exercise prices, upper (in usd per share) | $ / shares	$ 36.15
Options outstanding, number of options (in shares)	546
Options outstanding, weighted average remaining contractual life	5 years 6 months
Options exercisable, number of options (in shares)	495
Options exercisable, weighted average remaining contractual life	5 years 6 months
$38.03 to $45.76
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower (in usd per share) | $ / shares	$ 38.03
Range of exercise prices, upper (in usd per share) | $ / shares	$ 45.76
Options outstanding, number of options (in shares)	656
Options outstanding, weighted average remaining contractual life	4 years 10 months 24 days
Options exercisable, number of options (in shares)	656
Options exercisable, weighted average remaining contractual life	4 years 10 months 24 days
$46.20 to $56.05
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower (in usd per share) | $ / shares	$ 46.20
Range of exercise prices, upper (in usd per share) | $ / shares	$ 56.05
Options outstanding, number of options (in shares)	1,110
Options outstanding, weighted average remaining contractual life	4 years 9 months 18 days
Options exercisable, number of options (in shares)	1,110
Options exercisable, weighted average remaining contractual life	4 years 9 months 18 days

Stock-Based Awards - Stock Opti

Stock-Based Awards - Stock Option Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense recognized	$ 66,557	$ 65,830	$ 54,699
Stock options granted (in shares)	0
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total intrinsic value of options exercised	$ 25,800	9,200	18,200
Total grant date fair value of stock options vested	5,500	15,400	24,300
Compensation expense recognized	4,800	$ 14,000	23,000
Unrecognized compensation expense related to options	$ 600
Unrecognized compensation expense, weighted-average period of recognition	8 months 27 days
Aggregate grant date fair value of stock options granted			$ 1,800
Stock options granted (in shares)	0	0

Stock-Based Awards - Restricted

Stock-Based Awards - Restricted Stock Units (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Additional Information
Compensation expense recognized	$ 66,557	$ 65,830	$ 54,699
Restricted stock units
Number of Shares
Number of shares, outstanding at beginning of period (in shares)	3,790
Number of shares, granted (in shares)	2,227
Number of shares, forfeited (in shares)	(530)
Number of shares, vested (in shares)	(1,370)
Number of shares, outstanding at period end (in share)	4,117	3,790
Weighted Average Grant Date Fair Value
Weighted average grant date fair value, outstanding at beginning of period (in usd per share)	$ 37.22
Weighted average grant date fair value, granted (in usd per share)	46.17	$ 37.99	$ 37.49
Weighted average grant date fair value, forfeited (in usd per share)	39.07
Weighted average grant date fair value, vested (in usd per share)	36.87
Weighted average grant date fair value, outstanding at period end (in usd per share)	$ 41.94	$ 37.22
Additional Information
Fair value of restricted stock units vested	$ 49,900	$ 37,200	$ 24,700
Compensation expense recognized	53,200	$ 44,100	$ 31,900
Unrecognized compensation expense related to nonvested restricted stock units	$ 127,800
Unrecognized compensation expense, weighted-average period of recognition		2 years 10 months 24 days

Stock-Based Awards - Performanc

Stock-Based Awards - Performance Awards Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 66,557,000	$ 65,830,000	$ 54,699,000
Performance awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	5,500,000	$ 11,200,000	$ 2,600,000
Unrecognized compensation expense	$ 18,412,000
Unrecognized compensation expense, weighted-average period of recognition	2 years 11 months 19 days

Stock-Based Awards - Issuance o

Stock-Based Awards - Issuance of Awards Under New Compensation Award Structure (Details) - Performance awards - $ / shares	1 Months Ended					12 Months Ended
	Dec. 31, 2018	Apr. 30, 2018	Feb. 28, 2018	Mar. 31, 2017	Jul. 31, 2016	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period				3 years	3 years
Weighted average grant date fair value (in usd per share)				$ 41.73	$ 38.67
Shares issued (in shares)	0
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (in shares)				185,270	166,600
Shares outstanding (in share)				149,490,000	0
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (in shares)				555,810	499,800
Shares outstanding (in share)				448,470,000	0
Performance Period One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		3 years	3 years
Weighted average grant date fair value (in usd per share)		$ 39.54	$ 40.64
Performance Period One | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (in shares)		3,572	121,764
Shares outstanding (in share)		3,572,000	121,764,000
Performance Period One | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (in shares)		8,930	304,410
Shares outstanding (in share)		8,930,000	304,410,000
Performance Period Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		5 years	5 years
Weighted average grant date fair value (in usd per share)		$ 39.54	$ 40.64
Award expiration period						3 years
Performance Period Two | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (in shares)		53,572	411,412
Shares outstanding (in share)		53,572,000	411,412,000
Performance Period Two | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (in shares)		133,930	1,028,530
Shares outstanding (in share)		133,930,000	1,028,530,000
Third Anniversary | Performance Period Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Eligible share periodic vesting						33.33%
Fourth Anniversary | Performance Period Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Eligible share periodic vesting						33.33%
Fifth Anniversary | Performance Period Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Eligible share periodic vesting						33.33%

Stock-Based Awards - Schedule_2

Stock-Based Awards - Schedule of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 66,557	$ 65,830	$ 54,699
Cost of revenue
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	4,218	4,904	4,732
Sales and marketing
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	24,440	28,427	25,642
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	11,800	9,630	7,586
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	19,872	22,869	16,739
Restructuring
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 6,227	$ 0	$ 0

Income Taxes - Components of In

Income Taxes - Components of Income Before Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
United States									$ (21,174)	$ (32,853)	$ (39,107)
Foreign									(10,073)	(26,736)	(26,523)
Loss before income tax provision	$ (2,169)	$ (1,925)	$ (11,471)	$ (15,683)	$ (8,696)	$ (14,352)	$ (20,901)	$ (15,640)	$ (31,247)	$ (59,589)	$ (65,630)

Income Taxes - Components of _2

Income Taxes - Components of Income Tax Provision (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current income tax provision:
Federal									$ 0	$ 0	$ 0
State									204	114	105
Foreign									2,514	1,580	1,838
Total current income tax provision									2,718	1,694	1,943
Deferred income tax benefit:
Federal									0	0	0
State									0	0	0
Foreign									(123)	52	(736)
Total deferred income tax benefit									(123)	52	(736)
Total income tax provision (benefit)	$ 1,004	$ 522	$ 536	$ 533	$ 308	$ 503	$ 364	$ 571	$ 2,595	$ 1,746	$ 1,207

Income Taxes - Components of Ef

Income Taxes - Components of Effective Income Tax Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Reconciliation
U.S. Federal tax benefit at statutory rates									$ (6,562)	$ (20,260)	$ (22,310)
State income taxes, net of federal tax benefit									(248)	(806)	(855)
Foreign rate differential									2,764	5,220	3,711
Stock based compensation									3,029	3,182	4,467
Other permanent differences									280	(494)	(750)
Deferred adjustments / U.S. rate change									1,430	7,811	0
Other									130	262	1,494
Valuation allowance									1,772	6,831	15,450
Total income tax provision (benefit)	$ 1,004	$ 522	$ 536	$ 533	$ 308	$ 503	$ 364	$ 571	$ 2,595	$ 1,746	$ 1,207

Income Taxes - Components of De

Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Accrued expenses	$ 2,353	$ 2,371
Long-lived intangible assets and fixed assets — basis difference	22,947	19,884
Net operating loss carryforwards	82,017	80,615
Stock-based compensation	15,172	16,886
Deferred revenue	2,861	2,739
Convertible note hedge	0	1,467
Other	4,557	2,721
Total deferred tax assets	129,907	126,683
Valuation allowance	(117,058)	(118,606)
Deferred tax assets, net of valuation allowance	12,849	8,077
Deferred tax liabilities:
Prepaid expenses and deferred commissions	(10,831)	(5,672)
Convertible note discount	0	(1,074)
Other	(976)	(410)
Total deferred tax liabilities	(11,807)	(7,156)
Net deferred tax assets (liabilities)	$ 1,042	$ 921

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Net increase (decrease) to valuation allowance primarily due to additional net operating losses	$ (1,500,000)	$ 6,800,000	$ 15,500,000
Undistributed foreign earnings	3,100,000	3,300,000
Potential tax impact if undistributed foreign earnings were distributed	100,000	$ 100,000
Transition tax on undistributed earnings	0
Reduction in tax expense if unrecognized tax benefits are recognized	1,400,000
Decrease in unrecognized tax benefits and income tax due to resolution	1,200,000
Federal Tax Authority
Operating Loss Carryforwards [Line Items]
Federal, state and foreign net operating losses	261,800,000
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Federal, state and foreign net operating losses	269,500,000
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Federal, state and foreign net operating losses	$ 84,800,000

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits
Unrecognized tax benefit, beginning balance	$ 1,271	$ 276	$ 276
Additions for tax positions related to the current year	131	995	0
Unrecognized tax benefit, ending balance	$ 1,402	$ 1,271	$ 276

Restructuring Costs (Details)

Restructuring Costs (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 0	$ 221	$ 1,000	$ 7,725	$ 1,539	$ 0	$ 0	$ 0	$ 8,946	$ 1,539	$ 0
New Strategic Plan
Restructuring Cost and Reserve [Line Items]
Workforce reduction										6.00%
Restructuring costs									8,900	$ 1,500
Stock-Based Compensation Expense
Restructuring Cost and Reserve [Line Items]
Restructuring costs									6,200
Payroll Related Costs
Restructuring Cost and Reserve [Line Items]
Restructuring costs									$ 2,700

Segment and Geographic Inform_3

Segment and Geographic Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2018USD ($)segment	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Segment Reporting [Abstract]
Number of operating segments | segment									1
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 138,247	$ 134,014	$ 132,517	$ 133,113	$ 131,956	$ 121,796	$ 116,651	$ 111,582	$ 537,891	$ 481,985	$ 423,124
Property and equipment, net	77,254				20,817				77,254	20,817
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									343,205	313,729	284,657
Property and equipment, net	69,550				16,468				69,550	16,468
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment, net	3,558				3,378				3,558	3,378
All other countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									194,686	168,256	138,467
Property and equipment, net	$ 4,146				$ 971				4,146	971
Subscription revenue | Sales Revenue, Services, Net | Product Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									$ 473,052	$ 396,764	$ 339,756
Percentage of revenue to total									87.90%	82.30%	80.30%
Professional services revenue | Sales Revenue, Services, Net | Product Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									$ 64,839	$ 85,221	$ 83,368
Percentage of revenue to total									12.10%	17.70%	19.70%

401(k) Savings Plan (Details)

401(k) Savings Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
401(k) employer matching percentage	50.00%
Maximum 401(k) annual contributions by employer per employee	$ 2,400
401(k) vesting period	4 years
401(k) matching contribution expenses	$ 2,000,000	$ 2,000,000	$ 1,900,000

Commitments and Contingencies -

Commitments and Contingencies - Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Rent expense under operating leases	$ 9,800	$ 8,000	$ 7,800
Operating Leases
Total minimum lease payments, 2019	11,576
Total minimum lease payments, 2020	14,162
Total minimum lease payments, 2021	14,277
Total minimum lease payments, 2022	14,823
Total minimum lease payments, 2023	14,710
Total minimum lease payments, Thereafter	17,961
Total minimum lease payments	87,509
Financing Obligation
Total finance obligation due, 2019	4,800
Total finance obligation due, 2020	4,900
Total finance obligation due, 2021	4,900
Total finance obligation due, 2022	5,300
Total finance obligation due, 2023 and thereafter	$ 21,700

Commitments and Contingencies_2

Commitments and Contingencies - Letters of Credit (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Standby letters of credit | Building lease and other commitments
Loss Contingencies [Line Items]
Letter of credit outstanding	$ 7.7	$ 1.4

Commitments and Contingencies_3

Commitments and Contingencies - Additional Information (Detail) - Software Subscription Agreement $ in Millions	Dec. 31, 2018USD ($)
Loss Contingencies [Line Items]
Contractual commitment due within the next year	$ 17.8
Contractual commitment due within two years	8.8
Contractual commitment due within three years	$ 2.8

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transactions [Abstract]
Value of resources donated to related parties	$ 3.7	$ 3.4	$ 3.3

Subsequent Events (Detail)

Subsequent Events (Detail) - USD ($) $ in Millions	1 Months Ended		2 Months Ended	12 Months Ended
	Feb. 26, 2019	Jan. 31, 2019	Feb. 26, 2019	Dec. 31, 2018
Restricted stock units
Subsequent Event [Line Items]
Awards granted (in shares)				2,227,000
Software Subscription Agreement
Subsequent Event [Line Items]
Contractual commitment due within the next year				$ 17.8
Contractual commitment due within two years				8.8
Contractual commitment due within three years				$ 2.8
2010 Plan | Restricted stock units
Subsequent Event [Line Items]
Awards granted (in shares)				2,227,182
Subsequent Event | Performance Based Restricted Stock Units
Subsequent Event [Line Items]
Shares expected to be issued (in shares)	93,738		93,738
Award vesting period	3 years
Subsequent Event | Restricted stock units
Subsequent Event [Line Items]
Award vesting period			4 years
Awards granted (in shares)			251,928
Subsequent Event | Software Subscription Agreement
Subsequent Event [Line Items]
Contractual commitment due within the next year	$ 0.5		$ 0.5
Contractual commitment due within two years	1.1		1.1
Contractual commitment due within three years	1.1		1.1
Contractual commitment due within four years	1.1		1.1
Contractual commitment due in year five and thereafter	$ 2		$ 2
Subsequent Event | Employee Stock Purchase Plan
Subsequent Event [Line Items]
Share increase under plan (in shares)		588,856
Subsequent Event | 2010 Plan
Subsequent Event [Line Items]
Share increase under plan (in shares)		2,649,855
Subsequent Event | Maximum | Performance Based Restricted Stock Units
Subsequent Event [Line Items]
Shares expected to be issued (in shares)	234,345		234,345

Selected Quarterly Data (Unau_3

Selected Quarterly Data (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Unaudited Quarterly Consolidated Statements of Operations
Revenue	$ 138,247	$ 134,014	$ 132,517	$ 133,113	$ 131,956	$ 121,796	$ 116,651	$ 111,582	$ 537,891	$ 481,985	$ 423,124
Cost of revenue	34,793	36,171	36,365	37,020	37,889	35,708	35,321	33,949	144,349	142,867	135,752
Gross profit	103,454	97,843	96,152	96,093	94,067	86,088	81,330	77,633	393,542	339,118	287,372
Operating expenses:
Sales and marketing	52,354	53,215	59,821	59,245	60,750	60,554	62,073	56,894	224,635	240,271	225,781
Research and development	24,967	19,705	16,325	15,984	17,491	16,389	14,684	13,411	76,981	61,975	46,977
General and administrative	23,535	23,128	22,101	21,985	19,723	21,249	23,141	20,476	90,749	84,589	70,956
Restructuring	0	221	1,000	7,725	1,539	0	0	0	8,946	1,539	0
Total operating expenses	100,856	96,269	99,247	104,939	99,503	98,192	99,898	90,781	401,311	388,374	343,714
(Loss) income from operations	$ 2,598	$ 1,574	$ (3,095)	$ (8,846)	$ (5,436)	$ (12,104)	$ (18,568)	$ (13,148)	(7,769)	(49,256)	(56,342)
(Loss) income from operations per share, basic and diluted (usd per share)	$ 0.04	$ 0.03	$ (0.05)	$ (0.15)	$ (0.09)	$ (0.21)	$ (0.33)	$ (0.23)
Other income (expense):
Interest income (expense) and other income (expense), net	$ (4,767)	$ (3,499)	$ (8,376)	$ (6,837)	$ (3,260)	$ (2,248)	$ (2,333)	$ (2,492)	(23,478)	(10,333)	(9,288)
Loss before income tax provision	(2,169)	(1,925)	(11,471)	(15,683)	(8,696)	(14,352)	(20,901)	(15,640)	(31,247)	(59,589)	(65,630)
Income tax provision	(1,004)	(522)	(536)	(533)	(308)	(503)	(364)	(571)	(2,595)	(1,746)	(1,207)
Net loss	$ (3,173)	$ (2,447)	$ (12,007)	$ (16,216)	$ (9,004)	$ (14,855)	$ (21,265)	$ (16,211)	$ (33,842)	$ (61,335)	$ (66,837)
Net loss per share — basic and diluted (usd per share)	$ (0.05)	$ (0.04)	$ (0.21)	$ (0.28)	$ (0.16)	$ (0.26)	$ (0.37)	$ (0.29)	$ (0.58)	$ (1.07)	$ (1.20)
Weighted average common shares outstanding, basic and diluted (in shares)	58,649	58,699	57,844	57,425	57,826	57,627	56,935	56,642	58,159	57,262	55,595

Uncategorized Items - csod-2018

Label	Element	Value
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 18,934,000
Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 18,934,000