CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Comprehensive Income	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Treasury Stock	Noncontrolling Interest
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			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 | Accounting Standards Update 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 8)	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
Net income and comprehensive income	96,499	$ 96,499			96,499
Non-cash compensation	44,365			44,365
Purchase of treasury stock	$ (92,606)					$ (92,606)
Purchase of treasury stock (in shares)	(379,449)					(379,000)
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes	$ 2,217		$ 12	2,205
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes (in shares)			1,210,000
Cumulative effect adjustment | Accounting Standards Update 2014-09	1,373				1,373
Issuance of 0.625% Convertible Senior Notes, net	(4)			(4)
Acquisition of noncontrolling interest	(510)			79			(589)
Balance at Dec. 31, 2018	$ 346,208		$ 154	$ 1,134,227	$ (610,482)	$ (177,691)	$ 0
Balance (in shares) at Dec. 31, 2018			15,428,000			2,618,000
Increase (Decrease) in Stockholders' Equity
Interest rate	0.625%