CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Treasury Stock	Comprehensive Income (Loss)	Noncontrolling interest
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 (loss) income and comprehensive (loss) income				31,524		$ 31,524
Non-cash compensation	11,109		11,109
Purchase of treasury stock	(11,000)				$ (11,000)
Purchase of treasury stock (in shares)					30,000
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes	2,057	$ 5	2,052
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes (in shares)		473,000
Cumulative effect adjustment due to ASU 2014-09	1,373			1,373
Noncontrolling interest	(34)						(34)
Balance at Mar. 31, 2018	329,903	$ 147	1,100,743	(675,457)	$ (96,085)		555
Balance (in shares) at Mar. 31, 2018		14,691,000			2,269,000
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 (loss) income and comprehensive (loss) income	99,799
Purchase of treasury stock	$ (57,200)
Purchase of treasury stock (in shares)	205,310
Balance at Sep. 30, 2018	$ 376,466	$ 154	1,125,185	(607,182)	$ (142,268)		577
Balance (in shares) at Sep. 30, 2018		15,390,000			2,444,000
Balance at Mar. 31, 2018	329,903	$ 147	1,100,743	(675,457)	$ (96,085)		555
Balance (in shares) at Mar. 31, 2018		14,691,000			2,269,000
Increase (Decrease) in Stockholders' Equity
Net (loss) income and comprehensive (loss) income				42,547		42,547
Non-cash compensation	11,178		11,178
Purchase of treasury stock	(35,003)				$ (35,003)
Purchase of treasury stock (in shares)					127,000
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes	(1,225)	$ 4	(1,229)
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes (in shares)		447,000
Issuance of 0.625% Convertible Senior Notes, net	(4)		(4)
Noncontrolling interest	32						32
Balance at Jun. 30, 2018	347,428	$ 151	1,110,688	(632,910)	$ (131,088)		587
Balance (in shares) at Jun. 30, 2018		15,138,000			2,396,000
Increase (Decrease) in Stockholders' Equity
Net (loss) income and comprehensive (loss) income	25,728			25,728		25,728
Non-cash compensation	12,097		12,097
Purchase of treasury stock	(11,180)				$ (11,180)
Purchase of treasury stock (in shares)					48,000
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes	2,404	$ 3	2,401
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes (in shares)		252,000
Issuance of 0.625% Convertible Senior Notes, net	(1)		(1)
Noncontrolling interest	(10)						(10)
Balance at Sep. 30, 2018	376,466	$ 154	1,125,185	(607,182)	$ (142,268)		$ 577
Balance (in shares) at Sep. 30, 2018		15,390,000			2,444,000
Balance at Dec. 31, 2018	346,208	$ 154	1,134,227	(610,482)	$ (177,691)
Balance (in shares) at Dec. 31, 2018		15,428,000			2,618,000
Increase (Decrease) in Stockholders' Equity
Net (loss) income and comprehensive (loss) income				(512)		(512)
Non-cash compensation	14,053		14,053
Purchase of treasury stock	(3,976)				$ (3,976)
Purchase of treasury stock (in shares)					18,000
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes	(3,585)	$ 1	(3,586)
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes (in shares)		87,000
Balance at Mar. 31, 2019	352,188	$ 155	1,144,694	(610,994)	$ (181,667)
Balance (in shares) at Mar. 31, 2019		15,515,000			2,636,000
Balance at Dec. 31, 2018	346,208	$ 154	1,134,227	(610,482)	$ (177,691)
Balance (in shares) at Dec. 31, 2018		15,428,000			2,618,000
Increase (Decrease) in Stockholders' Equity
Net (loss) income and comprehensive (loss) income	15,970
Purchase of treasury stock	$ (4,300)
Purchase of treasury stock (in shares)	18,580
Balance at Sep. 30, 2019	$ 389,264	$ 156	1,165,597	(594,512)	$ (181,977)
Balance (in shares) at Sep. 30, 2019		15,635,000			2,637,000
Balance at Mar. 31, 2019	352,188	$ 155	1,144,694	(610,994)	$ (181,667)
Balance (in shares) at Mar. 31, 2019		15,515,000			2,636,000
Increase (Decrease) in Stockholders' Equity
Net (loss) income and comprehensive (loss) income				12,218		12,218
Non-cash compensation	15,982		15,982
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes	(6,501)	$ 1	(6,502)
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes (in shares)		89,000
Balance at Jun. 30, 2019	373,887	$ 156	1,154,174	(598,776)	$ (181,667)
Balance (in shares) at Jun. 30, 2019		15,604,000			2,636,000
Increase (Decrease) in Stockholders' Equity
Net (loss) income and comprehensive (loss) income	4,264			4,264		$ 4,264
Non-cash compensation	10,797		10,797
Purchase of treasury stock	(310)				$ (310)
Purchase of treasury stock (in shares)					1,000
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes	626	$ 0	626
Issuance of common stock for stock options, restricted stock awards and restricted stock units, net of withholding taxes (in shares)		31,000
Settlement of 0.625% Convertible Senior Notes	(2)		(2)
Exercise of Convertible Note Hedge	2		2
Balance at Sep. 30, 2019	$ 389,264	$ 156	$ 1,165,597	$ (594,512)	$ (181,977)
Balance (in shares) at Sep. 30, 2019		15,635,000			2,637,000