Debt - Long-Term Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Mar. 05, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Less – unamortized original issue discount	$ (15,641)		$ (18,264)
Less - deferred financing costs		$ (2,800)
Total debt, net of unamortized discounts	360,609		331,736
Current portion of long-term debt, net of unamortized discounts	(7,500)		(22,500)
Long-term debt, net of unamortized discounts	353,109		309,236
2015 Credit Agreement | 2015 Term Loan
Debt Instrument [Line Items]
Total long-term debt, gross			120,000
Less - deferred financing costs			(2,274)
Total debt, net of unamortized discounts			117,726
2018 Credit Agreement | 2018 Term Loan
Debt Instrument [Line Items]
Total long-term debt, gross	146,250
Less - deferred financing costs	(2,424)
Total debt, net of unamortized discounts	143,826	$ 150,000
Senior Convertible Notes 2016
Debt Instrument [Line Items]
Total long-term debt, gross	230,000		230,000
Less – unamortized original issue discount	(9,503)		(11,487)
Less - deferred financing costs	(3,714)		(4,503)
Total debt, net of unamortized discounts	$ 216,783		$ 214,010