CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Comprehensive Income	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Treasury Stock	Noncontrolling Interest [Member]
Balance at Dec. 31, 2014	$ 96,366		$ 129	$ 909,751	$ (798,171)	$ (15,343)	$ 0
Balance (in shares) at Dec. 31, 2014			12,855,000			1,468,000
Increase (Decrease) in Stockholders' Equity
Net income and comprehensive income	48,047	$ 48,047			48,047
Non-cash compensation	(8,508)			(8,508)
Purchase of treasury stock	$ (218)					$ (218)
Purchase of treasury stock (in shares)	5,250					6,000
Dividends	$ (11)			(11)
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes	(7,613)		$ (1)	7,614
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes (in shares)			158,000
Tax benefit from stock-based award activity	4,601			4,601
Proceeds from equity offering, net of offering costs	91,462		$ 9	91,453
Issuance of stock for equity offering (in shares)			853,000
Balance at Dec. 31, 2015	241,142		$ 139	1,006,688	(750,124)	$ (15,561)	0
Balance (in shares) at Dec. 31, 2015			13,866,000			1,474,000
Increase (Decrease) in Stockholders' Equity
Net income and comprehensive income	27,494	27,494			27,494
Non-cash compensation	(9,647)			(9,647)
Purchase of treasury stock	$ (48,524)					$ (48,524)
Purchase of treasury stock (in shares)	690,218					690,000
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes	$ (4,084)		$ (1)	4,085
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes (in shares)			89,000
Tax benefit from stock-based award activity	5,760			5,760
Balance at Dec. 31, 2016	231,435		$ 140	1,018,010	(722,630)	$ (64,085)	0
Balance (in shares) at Dec. 31, 2016			13,955,000			2,164,000
Increase (Decrease) in Stockholders' Equity
Net income and comprehensive income	15,578	$ 15,578
Non-cash compensation	23,361			23,361
Purchase of treasury stock	$ (21,000)					$ (21,000)
Purchase of treasury stock (in shares)	75,393					75,000
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes	$ (1,601)		$ (2)	(1,599)
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes (in shares)			263,000
Cumulative effect adjustment due to ASU 2016-09	985			2,287	(1,302)
Issuance of 0.625% Convertible Senior Notes, net	60,415			60,415
Convertible note hedge	(61,500)			(61,500)
Sale of warrants	43,410			43,410
Noncontrolling interest (Note 6)	589						589
Balance at Dec. 31, 2017	$ 294,874		$ 142	$ 1,087,582	$ (708,354)	$ (85,085)	$ 589
Balance (in shares) at Dec. 31, 2017			14,218,000			2,239,000
Increase (Decrease) in Stockholders' Equity
Interest rate	0.625%