Fair Value Measurement - Fair Value of Assets (Liabilities) Not Measured at Fair Value In Consolidated Balance Sheet - Additional Information (Details) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | ||||
|---|---|---|---|---|---|---|
Sep. 30, 2018 |
Jun. 30, 2018 |
Sep. 30, 2017 |
Sep. 30, 2018 |
Sep. 30, 2017 |
Dec. 31, 2017 |
|
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||||||
| Asset impairment charges | $ 0 | $ 0 | $ 20,098 | $ 0 | ||
| Fixed-Rate Long-Term Debt | ||||||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||||||
| Long term debt, carrying value | $ 180,000 | $ 180,000 | $ 265,000 | |||
| Variable Interest Entity, Not Primary Beneficiary | ||||||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||||||
| Asset impairment charges | $ 20,100 | |||||