Operating Leases (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Operating Leased Assets [Line Items]
Operating Leases, Rent Expense	$ 1,700	$ 0	$ 3,600	$ 0
Terminal Facilities
Operating Leased Assets [Line Items]
Operating Leases, Rent Expense	1,200	500	2,600	1,000
Terminal Facilities | Related Party
Operating Leased Assets [Line Items]
Operating Leases, Rent Expense	214	392	461	806
Related Party Transaction, Expenses from Transactions with Related Party	$ 200	$ 400	$ 500	$ 800