Consolidated Statements of Stockholders' Equity Statement - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional paid-in capital	Accumulated other comprehensive (loss) income	Retained earnings
Balance (shares) at Dec. 31, 2017		34,540
Balance at Dec. 31, 2017	$ 227,104	$ 35	$ 239,489		$ (12,420)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under equity compensation plans (shares)		516
Issuance of common stock under equity compensation plans	5,652		5,652
Stock-based compensation expense	2,936		2,936
Debt conversion, shares issued (in shares)		2,428
Issuance of shares in exchange for Convertible Senior Notes	118,075	$ 2	118,073
Reduction for equity component of Convertible Senior Notes exchanged	(53,867)		(53,867)
Repurchases of common stock (shares)		(73)
Repurchases of common stock	(3,232)		(3,232)
Changes in cumulative translation adjustment, net of tax	20			$ 20
Change in fair value of cash flow hedges, net of tax	0
Net income	33,958				33,958
Balance (shares) at Mar. 31, 2018		37,411
Balance at Mar. 31, 2018	330,646	$ 37	309,051	20	21,538
Balance (shares) at Dec. 31, 2018		39,386
Balance at Dec. 31, 2018	425,584	$ 39	363,921	(139)	61,763
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under equity compensation plans (shares)		444
Issuance of common stock under equity compensation plans	8,817	$ 1	8,816
Stock-based compensation expense	2,887		2,887
Repurchases of common stock (shares)		(24)
Repurchases of common stock	(1,476)		(1,476)
Changes in cumulative translation adjustment, net of tax	(248)			(248)
Change in fair value of cash flow hedges, net of tax	290			290
Net income	24,844
Balance (shares) at Mar. 31, 2019		39,806
Balance at Mar. 31, 2019	$ 460,698	$ 40	$ 374,148	$ (97)	$ 86,607