Related Party (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Due to Related Parties, Current	$ 100,000	$ 100,000
Operating Leases, Rent Expense	1,000,000	3,300,000	$ 8,300,000
Payments to Acquire Property, Plant, and Equipment	86,088,000	217,253,000	204,973,000
Related Party Transaction, Expenses from Transactions with Related Party	8,154,000	53,039,000	49,882,000
Related Party [Member]
Related Party Transaction [Line Items]
Payments for tractor purchase	4,300,000	58,599,000	46,562,000
proceeds from sale of trailers	(108,000)	(28,000)	(103,000)
proceeds from sale of tractors	0	(38,064,000)	(15,564,000)
Payments for parts and services	1,300,000	4,346,000	5,906,000
Operating Leases, Rent Expense	1,000,000	3,000,000	6,800,000
Payments to Acquire Property, Plant, and Equipment	0	21,555,000	2,825,000
Administrative Services Revenue	0	0	(516,000)
Revenue Equipment [Member] | Related Party [Member]
Related Party Transaction [Line Items]
Operating Leases, Rent Expense	813,000	3,223,000	6,842,000
Terminal Facilities [Member]
Related Party Transaction [Line Items]
Operating Leases, Rent Expense	2,200,000	3,900,000	4,200,000
Terminal Facilities [Member] | Related Party [Member]
Related Party Transaction [Line Items]
Operating Leases, Rent Expense	1,849,000	3,408,000	3,930,000
Related Party Transaction, Expenses from Transactions with Related Party	$ 1,900,000	$ 3,600,000	$ 3,900,000