Debt - Long-Term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Less – unamortized original issue discount	$ (18,264)	$ (23,007)
Less – unamortized original issue discount	0	(296)
Total debt, net of unamortized discounts	331,736	376,419
Current portion of long-term debt, net of unamortized discounts	(22,500)	(49,426)
Long-term debt, net of unamortized discounts	309,236	326,993
Credit Agreement | 2015 Term Loan
Debt Instrument [Line Items]
Total long-term debt, gross	120,000	135,000
Less - deferred financing costs	(2,274)	(3,489)
Total debt, net of unamortized discounts	117,726	131,511
Senior Convertible Notes 2016
Debt Instrument [Line Items]
Total long-term debt, gross	230,000	230,000
Less – unamortized original issue discount	(11,487)	(14,005)
Less - deferred financing costs	(4,503)	(5,513)
Total debt, net of unamortized discounts	$ 214,010	210,482
Senior Subordinated Convertible Notes 2010
Debt Instrument [Line Items]
Total long-term debt, gross		34,722
Less – unamortized original issue discount		(272)
Less - deferred financing costs		(24)
Total debt, net of unamortized discounts		$ 34,426