Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional paid-in capital [Member]	Accumulated other comprehensive income (loss) [Member]	Retained earnings [Member]	Convertible Debt [Member]
Beginning Balance at Dec. 31, 2015	$ 218,676	$ 33	$ 209,121	$ (31)	$ 9,553
Beginning Balance, shares at Dec. 31, 2015		33,323
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under equity compensation plans	9,365	$ 0	9,365
Issuance of common stock under equity compensation plans, shares		755
Stock-based compensation expense	7,134		7,134
Repurchases of common stock	(20,168)	$ 0	(20,168)
Repurchase of common stock, shares		(1,181)
Changes in cumulative translation adjustment, net of tax	(22)			(22)
Net income (loss)	(13,808)				(13,808)
Ending Balance at Dec. 31, 2016	200,630	$ 33	204,905	(53)	(4,255)
Ending Balance, shares at Dec. 31, 2016		32,897
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under equity compensation plans	26,079	$ 2	26,077
Issuance of common stock under equity compensation plans, shares		1,669
Stock-based compensation expense	9,048		9,048
Repurchases of common stock	(541)	$ 0	(541)
Repurchase of common stock, shares		(26)
Changes in cumulative translation adjustment, net of tax	53			53
Net income (loss)	(8,165)				(8,165)
Ending Balance at Dec. 31, 2017	227,104	$ 35	239,489	0	(12,420)
Ending Balance, shares at Dec. 31, 2017		34,540
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under equity compensation plans	17,047	$ 0	17,047
Issuance of common stock under equity compensation plans, shares		1,237
Stock-based compensation expense	10,078		10,078
Repurchase of Convertible Senior Notes	(547)
Repurchases of common stock	(4,344)	$ 0	(4,344)
Repurchase of common stock, shares		(90)
Changes in cumulative translation adjustment, net of tax	(139)			(139)
Issuance of shares in exchange for Convertible Senior Notes	200,219	$ 4	200,215
Number of shares of common stock issued						3,699
Tax impact from the conversion of Convertible Senior Notes	2,162		2,162
Reduction for equity component of Convertible Senior Notes exchanged	(100,726)		(100,726)
Net income (loss)	74,183				74,183
Ending Balance at Dec. 31, 2018	$ 425,584	$ 39	$ 363,921	$ (139)	$ 61,763
Ending Balance, shares at Dec. 31, 2018		39,386