Debt - Summary (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Debt
Total long-term debt	$ 990,480	$ 991,918
Less: current maturities	17,500	17,500
Long-term debt, net of current maturities	972,980	974,418
2023 Senior Notes
Debt
Total long-term debt	488,754	488,481
2015 Term Loan Facility
Debt
Total long-term debt	328,904	332,688
2.5 Percent Convertible Notes
Debt
Total long-term debt	$ 172,822	$ 170,749