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]
Beginning Balance at Dec. 31, 2014	$ 245,011	$ 34	$ 229,374	$ (29)	$ 15,632
Beginning Balance, shares at Dec. 31, 2014		34,433
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under equity compensation plans	3,318	$ 0	3,318	0
Issuance of common stock under equity compensation plans, shares		308
Issuance of common stock under equity compensation plans	571		571	0	0
Tax impact from the issuance of convertible senior notes	6,791		6,791
Stock-based compensation expense	(30,934)		(30,933)
Repurchase of common stock, shares		(1,418)
Repurchases of common stock	(2)			(2)
Net loss	(6,079)				(6,079)
Ending Balance at Dec. 31, 2015	218,676	$ 33	209,121	(31)	9,553
Ending 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
Tax impact from the issuance of convertible senior notes	7,134		7,134
Stock-based compensation expense	(20,168)	$ 0	(20,168)
Repurchase of common stock, shares		(1,181)
Repurchases of common stock	(22)			(22)
Net 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
Tax impact from the issuance of convertible senior notes	9,048		9,048
Stock-based compensation expense	(541)	$ 0	(541)
Repurchase of Convertible Senior Notes	547
Repurchase of common stock, shares		(26)
Repurchases of common stock	53			53
Net loss	(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