CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock	Additional Paid-in-Capital	Accumulated Other Comprehensive Income	Accumulated Deficit	Treasury Stock	Total
Balance at Dec. 31, 2018	$ 36	$ 378,352	$ 738	$ (205,134)	$ (132)	$ 173,860
Balance (in shares) at Dec. 31, 2018	36,135				(28)
Stockholders' Deficit
Common stock issued under stock plans		5,406				5,406
Common stock issued under stock plans (in shares)	226
Stock-based compensation		7,129				7,129
Other comprehensive income			436			436
Net loss				(1,342)		(1,342)
Balance at Mar. 31, 2019	$ 36	390,887	1,174	(206,476)	$ (132)	185,489
Balance (in shares) at Mar. 31, 2019	36,361				(28)
Balance at Dec. 31, 2018	$ 36	378,352	738	(205,134)	$ (132)	173,860
Balance (in shares) at Dec. 31, 2018	36,135				(28)
Stockholders' Deficit
Other comprehensive income						495
Net loss						(7,651)
Balance at Jun. 30, 2019	$ 37	399,452	1,233	(212,785)	$ (132)	187,805
Balance (in shares) at Jun. 30, 2019	36,666				(28)
Balance at Mar. 31, 2019	$ 36	390,887	1,174	(206,476)	$ (132)	185,489
Balance (in shares) at Mar. 31, 2019	36,361				(28)
Stockholders' Deficit
Common stock issued under stock plans	$ 1	318				319
Common stock issued under stock plans (in shares)	305
Stock-based compensation		8,247				8,247
Other comprehensive income			59			59
Net loss				(6,309)		(6,309)
Balance at Jun. 30, 2019	$ 37	399,452	1,233	(212,785)	$ (132)	187,805
Balance (in shares) at Jun. 30, 2019	36,666				(28)
Balance at Dec. 31, 2019	$ 44	861,740	1,330	(189,710)	$ (132)	$ 673,272
Balance (in shares) at Dec. 31, 2019	43,530				(28)	43,502
Stockholders' Deficit
Common stock issued under stock plans		4,220				$ 4,220
Common stock issued under stock plans (in shares)	589
Stock-based compensation		17,176				17,176
Other comprehensive income			689			689
Net loss				(54,058)		(54,058)
Balance at Mar. 31, 2020	$ 44	883,136	2,019	(243,768)	$ (132)	641,299
Balance (in shares) at Mar. 31, 2020	44,119				(28)
Balance at Dec. 31, 2019	$ 44	861,740	1,330	(189,710)	$ (132)	$ 673,272
Balance (in shares) at Dec. 31, 2019	43,530				(28)	43,502
Stockholders' Deficit
Other comprehensive income						$ 1,137
Net loss						(93,952)
Balance at Jun. 30, 2020	$ 45	943,706	2,467	(283,662)	$ (132)	$ 662,424
Balance (in shares) at Jun. 30, 2020	44,578				(28)	44,550
Balance at Mar. 31, 2020	$ 44	883,136	2,019	(243,768)	$ (132)	$ 641,299
Balance (in shares) at Mar. 31, 2020	44,119				(28)
Stockholders' Deficit
Common stock issued under stock plans	$ 1	1,633				1,634
Common stock issued under stock plans (in shares)	459
Stock-based compensation		13,062				13,062
Equity component of convertible senior notes, net of transaction costs of $3,267 and taxes of $12,891		81,554				81,554
Purchase of capped calls related to issuance of convertible senior notes		(35,679)				(35,679)
Other comprehensive income			448			448
Net loss				(39,894)		(39,894)
Balance at Jun. 30, 2020	$ 45	$ 943,706	$ 2,467	$ (283,662)	$ (132)	$ 662,424
Balance (in shares) at Jun. 30, 2020	44,578				(28)	44,550