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 (in shares) at Dec. 31, 2017		34,540
Balance at Dec. 31, 2017	$ 227,104	$ 35	$ 239,489	$ 0	$ (12,420)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under equity compensation plans (in shares)		516
Issuance of common stock under equity compensation and benefit 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
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments	(53,867)		(53,867)
Repurchases of common stock (in shares)		(73)
Repurchases of common stock	(3,232)		(3,232)
Changes in cumulative translation adjustment, net of tax	20			20
Net income (loss)	33,958				33,958
Balance (in shares) at Mar. 31, 2018		37,411
Balance at Mar. 31, 2018	330,646	$ 37	309,051	20	21,538
Balance (in shares) at Dec. 31, 2017		34,540
Balance at Dec. 31, 2017	227,104	$ 35	239,489	0	(12,420)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Changes in cumulative translation adjustment, net of tax	6
Net income (loss)	30,882
Balance (in shares) at Jun. 30, 2018		39,001
Balance at Jun. 30, 2018	368,908	$ 39	350,401	6	18,462
Balance (in shares) at Mar. 31, 2018		37,411
Balance at Mar. 31, 2018	330,646	$ 37	309,051	20	21,538
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under equity compensation plans (in shares)		326
Issuance of common stock under equity compensation and benefit plans	3,898		3,898
Stock-based compensation expense	2,579		2,579
Debt conversion, shares issued (in shares)		1,270
Issuance of shares in exchange for Convertible Senior Notes	82,110	$ 2	82,108
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments	(46,860)		(46,860)
Repurchases of common stock (in shares)		(6)
Repurchases of common stock	(375)		(375)
Changes in cumulative translation adjustment, net of tax	(14)			(14)
Net income (loss)	(3,076)				(3,076)
Balance (in shares) at Jun. 30, 2018		39,001
Balance at Jun. 30, 2018	368,908	$ 39	350,401	6	18,462
Balance (in 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 (in shares)		444
Issuance of common stock under equity compensation and benefit plans	8,817	$ 1	8,816
Stock-based compensation expense	2,887		2,887
Repurchases of common stock (in shares)		(24)
Repurchases of common stock	(1,476)		(1,476)
Other comprehensive gain (loss), net of tax	42			42
Net income (loss)	24,844				24,844
Balance (in shares) at Mar. 31, 2019		39,806
Balance at Mar. 31, 2019	460,698	$ 40	374,148	(97)	86,607
Balance (in 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]
Changes in cumulative translation adjustment, net of tax	(154)
Net income (loss)	26,114
Balance (in shares) at Jun. 30, 2019		41,418
Balance at Jun. 30, 2019	509,963	$ 41	421,996	49	87,877
Balance (in shares) at Mar. 31, 2019		39,806
Balance at Mar. 31, 2019	460,698	$ 40	374,148	(97)	86,607
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under equity compensation plans (in shares)		122
Issuance of common stock under equity compensation and benefit plans	1,433		1,433
Stock-based compensation expense	3,309		3,309
Debt conversion, shares issued (in shares)		1,497
Issuance of shares in exchange for Convertible Senior Notes	86,428	$ 1	86,427
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments	(43,516)		(43,516)
Tax impact from the conversion of Convertible Senior Notes	590		590
Repurchases of common stock (in shares)		(7)
Repurchases of common stock	(395)		(395)
Other comprehensive gain (loss), net of tax	146			146
Changes in cumulative translation adjustment, net of tax	94
Net income (loss)	1,270
Balance (in shares) at Jun. 30, 2019		41,418
Balance at Jun. 30, 2019	$ 509,963	$ 41	$ 421,996	$ 49	$ 87,877