CONSOLIDATED STATEMENTS OF REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Redeemable Convertible Preferred Stock
Balances at Dec. 31, 2013	$ (46,276)	$ 229	$ 18,591	$ (652)	$ 10	$ (64,454)	$ 71,369
Balances (in shares) at Dec. 31, 2013		23,710		(535)			23,598
Issuance of common stock upon initial public offering, net of issuance costs	103,090	$ 128	102,962
Issuance of common stock upon initial public offering, net of issuance costs (in shares)		12,778
Accretion of redeemable convertible preferred stock	(18)		(18)				$ 18
Conversion of preferred stock to common stock upon initial public offering	71,387	$ 343	71,044				$ (71,387)
Conversion of preferred stock to common stock upon initial public offering (in shares)		34,323					(23,598)
Issuance of common stock for acquisition of Zopim	10,892	$ 9	10,883
Issuance of common stock for acquisition of Zopim (in shares)		902
Issuance of common stock upon exercise of stock options	4,970	$ 32	4,938
Issuance of common stock upon exercise of stock options (in shares)		3,207
Issuance of common stock for settlement of restricted stock units (RSUs)	0	$ 5	(5)
Issuance of common stock for settlement of restricted stock units (RSUs) (in shares)		517
Shares withheld related to net share settlement of RSUs	(2,118)	$ (1)	(2,117)
Shares withheld related to net share settlement of RSUs (in shares)		(147)
Issuance of common stock upon early exercise of stock options (in shares)		309
Vesting of early exercised stock options	1,512	$ 5	1,507
Issuance of common stock in connection with employee stock purchase plans	3,271	$ 4	3,267
Issuance of common stock in connection with employee stock purchase plans (in shares)		428
Issuance of common stock upon exercise of warrants	0	$ 1	(1)
Issuance of common stock upon exercise of warrants (in shares)		111
Repurchase of common stock (in shares)		(4)
Share-based compensation	34,615		34,615
Tax benefit from share-based award activity	334		334
Other comprehensive loss, net of income taxes	(538)				(538)
Net loss	(67,415)					(67,415)
Balances at Dec. 31, 2014	113,706	$ 755	246,000	$ (652)	(528)	(131,869)	$ 0
Balances (in shares) at Dec. 31, 2014		76,134		(535)			0
Issuance of common stock upon initial public offering, net of issuance costs	190,096	$ 88	190,008
Issuance of common stock upon initial public offering, net of issuance costs (in shares)		8,780
Issuance of common stock upon exercise of stock options	10,613	$ 33	10,580
Issuance of common stock upon exercise of stock options (in shares)		3,275
Issuance of common stock for settlement of restricted stock units (RSUs)	(609)	$ 17	(626)
Issuance of common stock for settlement of restricted stock units (RSUs) (in shares)		1,655
Vesting of early exercised stock options	1,046		1,046
Issuance of common stock in connection with employee stock purchase plans	9,375	$ 12	9,363
Issuance of common stock in connection with employee stock purchase plans (in shares)		1,019
Repurchase of common stock (in shares)		(2)
Share-based compensation	54,363		54,363
Tax benefit from share-based award activity	449		449
Other comprehensive loss, net of income taxes	(1,697)				(1,697)
Net loss	(84,052)					(84,052)
Balances at Dec. 31, 2015	293,290	$ 905	511,183	$ (652)	(2,225)	(215,921)	$ 0
Balances (in shares) at Dec. 31, 2015		90,861		(535)			0
Issuance of common stock upon exercise of stock options	$ 25,435	$ 29	25,406
Issuance of common stock upon exercise of stock options (in shares)	2,924	2,924
Issuance of common stock for settlement of restricted stock units (RSUs)	$ (803)	$ 29	(832)
Issuance of common stock for settlement of restricted stock units (RSUs) (in shares)		2,894
Vesting of early exercised stock options	629	$ 1	628
Issuance of common stock in connection with employee stock purchase plans	$ 10,892	$ 7	10,885
Issuance of common stock in connection with employee stock purchase plans (in shares)		554
Repurchase of common stock (in shares)	(38)	(38)
Share-based compensation	$ 76,419		76,419
Tax benefit from share-based award activity	337		337
Other comprehensive loss, net of income taxes	(2,972)				(2,972)
Net loss	(103,799)
Balances at Dec. 31, 2016	$ 299,428	$ 971	$ 624,026	$ (652)	$ (5,197)	$ (319,720)	$ 0
Balances (in shares) at Dec. 31, 2016		97,195		(535)			0