Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Environmental remediation liabilities - discounted	$ 42,800		$ 42,800	$ 28,100
Accrual for environmental loss contingencies - weighted-average discount rate	3.70%		3.70%	3.60%
Environmental remediation liabilities - undiscounted	$ 84,700		$ 84,700	$ 68,200
Legal accrual	10,416	$ 17,600	28,044
Tax indemnification liability	$ 25,100		25,100	$ 42,700
Minimum
Loss Contingencies [Line Items]
Potential revision on future environmental remediation costs before tax			10,000
Maximum
Loss Contingencies [Line Items]
Potential revision on future environmental remediation costs before tax			$ 25,000