Related Party (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Related Party Transaction [Line Items]
Due to Related Parties, Current	$ 3,200		$ 3,200		$ 100
Receipts for tractor sales			0	$ 3,335
Operating Leases, Rent Expense	800	$ 2,200	2,700	6,800
related party payment for terminal purchase	4,875		4,875	2,825
Due from Related Parties, Current	1,600		1,600		$ 0
Costs and Expenses, Related Party	14,448	3,028	30,880	21,470
Related Party
Related Party Transaction [Line Items]
Payments for tractor purchase	20,687	4,707	45,582	16,533
Operating Leases, Rent Expense	767	1,784	2,651	5,430
Payments for parts and services	1,224	1,368	3,650	4,275
Administrative Services Revenue	0	(141)	0	(423)
Terminal Facilities
Related Party Transaction [Line Items]
Operating Leases, Rent Expense	900	1,000	3,000	3,200
Terminal Facilities | Related Party
Related Party Transaction [Line Items]
Operating Leases, Rent Expense	833	958	2,753	2,975
Tractors [Member] | Related Party
Related Party Transaction [Line Items]
Receipts for tractor sales	$ (9,035)	(5,545)	(28,603)	(10,042)
Trailers [Member] | Related Party
Related Party Transaction [Line Items]
Receipts for tractor sales		$ (103)	$ (28)	$ (103)