Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock	Treasury Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income	Total
Balance at the beginning of the period at Dec. 31, 2015	$ 410	$ (9,222)	$ 767,137	$ (45,058)	$ 1,348	$ 714,615
Balance (in shares) at Dec. 31, 2015	40,996	469
Increase (Decrease) in Stockholders' Equity
Net loss				(122,027)		(122,027)
Other comprehensive income (loss), net of tax					429	429
Share-based compensation expense			15,741			15,741
Net issuance under employee stock plans	$ (3)	$ 19,948	(20,890)			(945)
Net issuance under employee stock plans (in shares)	(281)	(1,072)
Purchases of common stock		$ (13,035)				(13,035)
Purchase of common stock (in shares)		730
Balance at the end of the period at Dec. 31, 2016	$ 407	$ (2,309)	763,303	(161,474)	1,777	601,704
Balance (in shares) at Dec. 31, 2016	40,715	127
Increase (Decrease) in Stockholders' Equity
Cumulative effect of change in accounting principle | ASU 2016-09			1,315	(1,315)
Cumulative effect of change in accounting principle | ASU 2014-09, Revenue from Contracts with Customers				6,926		6,926
Net loss				(51,396)		(51,396)
Other comprehensive income (loss), net of tax					35	35
Share-based compensation expense			24,396			24,396
Net issuance under employee stock plans	$ 3	$ 4,043	(9,795)			(5,749)
Net issuance under employee stock plans (in shares)	313	(245)
Stock issuance for business acquisition	$ 72		228,800			228,872
Stock issuance for business acquisition (in shares)	7,201
Convertible Senior Notes, equity component			45,249			45,249
Purchases of common stock		$ (3,018)				(3,018)
Purchase of common stock (in shares)		203
Balance at the end of the period at Dec. 31, 2017	$ 482	$ (1,284)	1,051,953	(212,870)	1,812	840,093
Balance (in shares) at Dec. 31, 2017	48,229	85
Increase (Decrease) in Stockholders' Equity
Net loss				(407,088)		(407,088)
Other comprehensive income (loss), net of tax					8	8
Share-based compensation expense			16,074			16,074
Net issuance under employee stock plans	$ 3	$ 6,721	(6,702)	(25)		(3)
Net issuance under employee stock plans (in shares)	318	(512)
Purchases of common stock		$ (11,309)				(11,309)
Purchase of common stock (in shares)		950
Balance at the end of the period at Dec. 31, 2018	$ 485	$ (5,872)	$ 1,061,325	$ (619,983)	$ 1,820	$ 437,775
Balance (in shares) at Dec. 31, 2018	48,547	523