CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common stock and additional paid-in capital:	Treasury stock:	Accumulated other comprehensive loss:	Accumulated deficit:
Beginning balances at Dec. 31, 2018	$ 380,087	$ 703,023	$ 0	$ (844)	$ (322,093)
Stock-based compensation		24,097
Exercise of employee stock options		1,686
Issuance of common stock, purchase plan		1,427
Payments for taxes related to net share settlement of equity awards		(8,181)
Retirement of treasury stock		(59,766)	85,539		(25,773)
Repurchase of common stock			(85,539)
Other comprehensive income (loss)	(42)			(42)
Net loss	(27,497)				(27,497)
Ending balance at Sep. 30, 2019	286,037	662,286	0	(886)	(375,363)
Beginning balances at Jun. 30, 2019	304,982	665,666	0	(799)	(359,885)
Stock-based compensation		7,768
Exercise of employee stock options		50
Payments for taxes related to net share settlement of equity awards		(1,720)
Retirement of treasury stock		(9,478)	14,593		(5,115)
Repurchase of common stock			(14,593)
Other comprehensive income (loss)	(87)			(87)
Net loss	(10,363)				(10,363)
Ending balance at Sep. 30, 2019	286,037	662,286	0	(886)	(375,363)
Beginning balances at Dec. 31, 2019	285,222	671,061	0	(916)	(384,923)
Stock-based compensation		21,374
Exercise of employee stock options		529
Issuance of common stock for services provided		456
Issuance of common stock, purchase plan		1,050
Payments for taxes related to net share settlement of equity awards		(5,456)
Other comprehensive income (loss)	(129)			(129)
Net loss	(40,076)				(40,076)
Ending balance at Sep. 30, 2020	262,970	689,014	0	(1,045)	(424,999)
Beginning balances at Jun. 30, 2020	262,345	684,286	0	(1,160)	(420,781)
Stock-based compensation		6,584
Exercise of employee stock options		45
Issuance of common stock for services provided		228
Payments for taxes related to net share settlement of equity awards		(2,129)
Other comprehensive income (loss)	115			115
Net loss	(4,218)				(4,218)
Ending balance at Sep. 30, 2020	$ 262,970	$ 689,014	$ 0	$ (1,045)	$ (424,999)