Operating Leases (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating Leased Assets [Line Items]
Operating Leases, Rent Expense	$ 900	$ 3,800	$ 4,500	$ 3,800
Terminal Facilities
Operating Leased Assets [Line Items]
Operating Leases, Rent Expense	1,200	1,500	3,800	2,500
Terminal Facilities | Related Party
Operating Leased Assets [Line Items]
Operating Leases, Rent Expense	251	421	712	1,227
Related Party Transaction, Expenses from Transactions with Related Party	$ 300	$ 400	$ 700	$ 1,200