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 (in shares)					30,000
Purchase of treasury stock	(11,000)				$ (11,000)
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	$ 74,071
Purchase of treasury stock (in shares)	156,731
Purchase of treasury stock	$ (46,000)
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
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		42,547
Non-cash compensation	11,178		11,178
Purchase of treasury stock (in shares)					127,000
Purchase of treasury stock	(35,003)				$ (35,003)
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
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 (in shares)					18,000
Purchase of treasury stock	(3,976)				$ 3,976
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	$ 11,706
Purchase of treasury stock (in shares)	17,501
Purchase of treasury stock	$ (4,000)
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
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		$ 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