Related Party (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Related Party Transaction [Line Items]
Due to Related Parties, Current	$ 1,300		$ 1,300		$ 100
Receipts for tractor sales			0	$ 3,335
Operating Leases, Rent Expense	800	$ 2,300	1,900	4,600
related party payment for terminal purchase	4,875	2,825	4,875	2,825
Due from Related Parties, Current	500		500		$ 0
Costs and Expenses, Related Party	19,456	6,048	16,432	18,591
Related Party
Related Party Transaction [Line Items]
Payments for tractor purchase	22,795	505	24,895	11,988
Receipts for tractor sales	(11,041)	(1,299)	(19,567)	(4,497)
Operating Leases, Rent Expense	799	1,817	1,884	3,646
Payments for parts and services	1,065	1,364	2,426	2,906
Administrative Services Revenue	0	(141)	0	(282)
Terminal Facilities
Related Party Transaction [Line Items]
Operating Leases, Rent Expense	1,000	1,000	2,100	2,100
Terminal Facilities | Related Party
Related Party Transaction [Line Items]
Operating Leases, Rent Expense	$ 963	$ 977	$ 1,900	$ 2,000