CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total		Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning Balance at Dec. 31, 2016	$ 33,021		$ 1	$ 186,494	$ 87	$ (153,561)
Begining balance, Shares at Dec. 31, 2016			100,486,000
Common stock issued upon stock option exercise	$ 153			153
Common stock issued upon stock option exercise, Shares	35,352		35,000
Common stock issued upon vesting of restricted stock units, net	$ (6,934)			(6,934)
Common stock issued upon vesting of restricted stock units, net, Shares			879,000
Repurchase of common stock	(144)			(144)
Repurchase of common stock, Shares			(11,791)
Forfeiture of restricted stock awards	(80)			(80)
Forfeiture of restricted stock awards, Shares			(5,000)
Stock-based compensation expense	38,105			38,105
Comprehensive loss	(68)	[1]			(68)
Net loss	(24,010)					(24,010)
Ending balance at Dec. 31, 2017	40,043		$ 1	217,594	19	(177,571)
Ending balance, Shares at Dec. 31, 2017			101,383,000
Cumulative-effect adjustment upon adoption | Accounting Standards Update 2017-09				(43)		43
Issuance of common stock in connection with initial public offering, net	225,336		$ 0	225,336	0	0
Issuance of common stock in connection with initial public offering, net, Shares			20,583,000
Common stock issued upon stock option exercise	$ 494			494
Common stock issued upon stock option exercise, Shares	81,849		82,000
Common stock issued upon vesting of restricted stock units, net	$ (25,807)			(25,807)
Common stock issued upon vesting of restricted stock units, net, Shares			3,771,000
Repurchase of common stock	(16)			(16)
Repurchase of common stock, Shares			(1,159)
Stock-based compensation expense	134,379			134,379
Comprehensive loss	(306)	[1]			(306)
Net loss	(154,740)					(154,740)
Ending balance at Dec. 31, 2018	219,383		$ 1	551,937	(287)	(332,268)
Ending balance, Shares at Dec. 31, 2018			125,818,000
Cumulative-effect adjustment upon adoption | ASC 842	3,411					3,411
Common stock issued upon stock option exercise	$ 47,678			47,678
Common stock issued upon stock option exercise, Shares	3,733,401		3,733,000
Common stock issued upon vesting of restricted stock units, net, Shares			3,661,000
Common stock issued in connection with acquisition	$ 36,204			36,204
Common stock issued in connection with acquisition, shares			2,320,000
Common stock issued under employee stock purchase plan	5,344			5,344
Common stock issued under employee stock purchase plan, shares			506,000
Stock-based compensation expense	63,748			63,748
Comprehensive loss	(157)	[1]			(157)
Other	232			232
Other, shares			16,000
Net loss	(73,859)					(73,859)
Ending balance at Dec. 31, 2019	$ 301,984		$ 1	$ 705,143	$ (444)	$ (402,716)
Ending balance, Shares at Dec. 31, 2019			136,054,000

[1] Net of tax effect which was not material.