CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Treasury Stock	Accumulated Deficit	Total
BALANCE at Dec. 31, 2016	$ 9	$ 383,193		$ (307,621)	$ 75,581
BALANCE (in shares) at Dec. 31, 2016	89,066,031
Issuance of common stock for stock option exercises		3,287			$ 3,287
Issuance of common stock for stock option exercises (in shares)	1,172,409				1,172,409
Vesting of early exercised stock options and restricted stock (in shares)	2,477
Issuance of common stock pursuant to the Employee Stock Purchase Plan		4,562			$ 4,562
Issuance of common stock pursuant to the Employee Stock Purchase Plan (in shares)	1,676,158
Issuance of common stock pursuant to the Employee Stock-Settled Bonus Plans		8,272			8,272
Issuance of common stock pursuant to the Employee Stock-Settled Bonus Plans (in shares)	1,688,097
Shares withheld for net settlement of Stock-Settled Bonus Plans		(3,149)			(3,149)
Shares withheld for net settlement of Stock-Settled Bonus Plans (in shares)	(677,547)
Vesting of restricted stock units	$ 1				1
Vesting of restricted stock units (in shares)	4,276,325
Stock-based compensation		24,360			24,360
Net loss				(53,362)	(53,362)
BALANCE at Dec. 31, 2017	$ 10	420,525		(360,983)	59,552
BALANCE (in shares) at Dec. 31, 2017	97,203,950
Issuance of common stock for stock option exercises		6,520			$ 6,520
Issuance of common stock for stock option exercises (in shares)	2,488,544				2,488,544
Issuance of common stock pursuant to the Employee Stock Purchase Plan		4,548			$ 4,548
Issuance of common stock pursuant to the Employee Stock Purchase Plan (in shares)	1,597,778
Issuance of common stock pursuant to the Employee Stock-Settled Bonus Plans	$ 1	9,621			9,622
Issuance of common stock pursuant to the Employee Stock-Settled Bonus Plans (in shares)	1,973,386
Shares withheld for net settlement of equity awards		(6,376)			(6,376)
Shares withheld for net settlement of equity awards (in shares)	(1,294,360)
Repurchase of common stock			$ (3,831)		$ (3,831)
Repurchase of common stock (in shares)	(821,888)				(821,888)
Vesting of restricted stock units (in shares)	5,059,135
Stock-based compensation		27,166			$ 27,166
Net loss				(43,084)	(43,084)
BALANCE at Dec. 31, 2018	$ 11	462,004	(3,831)	(404,067)	54,117
BALANCE (in shares) at Dec. 31, 2018	106,206,545
Issuance of common stock for stock option exercises		5,513			$ 5,513
Issuance of common stock for stock option exercises (in shares)	1,349,694				1,349,694
Issuance of common stock pursuant to the Employee Stock Purchase Plan		4,132			$ 4,132
Issuance of common stock pursuant to the Employee Stock Purchase Plan (in shares)	1,048,302
Issuance of common stock pursuant to the Employee Stock-Settled Bonus Plans		10,485			10,485
Issuance of common stock pursuant to the Employee Stock-Settled Bonus Plans (in shares)	2,170,855
Shares withheld for net settlement of equity awards		(5,892)			(5,892)
Shares withheld for net settlement of equity awards (in shares)	(1,147,904)
Repurchase of common stock			(11,310)		$ (11,310)
Repurchase of common stock (in shares)	(2,137,874)				(2,137,874)
Vesting of restricted stock units (in shares)	5,235,773
Stock-based compensation		27,799			$ 27,799
Net loss				(48,846)	(48,846)
BALANCE at Dec. 31, 2019	$ 11	$ 504,041	$ (15,141)	$ (452,913)	$ 35,998
BALANCE (in shares) at Dec. 31, 2019	112,725,391