Long-Term Debt - Tabular Disclosure (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Long-Term Debt
Total principal amount	$ 710,148	$ 737,148
Less: unamortized discount	(5,481)	(6,240)
Less: debt issuance costs, net	(5,927)	(6,899)
Total carrying amount	698,740	724,009
2022 Notes | Senior notes
Long-Term Debt
Total principal amount	409,148	409,148
2023 Notes | Senior notes
Long-Term Debt
Total principal amount	150,000	150,000
Revolving credit facility | Revolver | Line of credit
Long-Term Debt
Total principal amount	$ 151,000	$ 178,000