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