Leases - Additional Information (Details) - USD ($) $ in Millions			12 Months Ended
	Sep. 01, 2016	Dec. 01, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Capital Leased Assets [Line Items]
Monthly lease payment	$ 0.4
Rental expense			$ 0.3	$ 0.5	$ 0.6
Short-term payment obligations			$ 5.8	$ 5.9
Port Neches Tank Lease
Capital Leased Assets [Line Items]
Monthly lease payment	$ 0.4
Minimum actual and premises operating cost difference percentage required for lease adjustment (more than)		5.00%
Imputed interest rate on capital portion of lease		15.00%