Fair Value Measurement - Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis (Details) - Nonrecurring - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Principal Amount | 2022 Notes | Senior notes
Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis
Debt	$ 409,148	$ 409,148
Principal Amount | 2023 Notes | Senior notes
Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis
Debt	150,000	150,000
Principal Amount | Revolving credit facility | Revolver | Line of credit
Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis
Debt	151,000	178,000
Level 3 | Total | Revolving credit facility | Revolver | Line of credit
Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis
Debt	151,000	178,000
Level 1 | Total | 2022 Notes | Senior notes
Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis
Debt	338,496	393,150
Level 2 | Total | 2023 Notes | Senior notes
Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis
Debt	$ 124,560	$ 153,375