Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net income	$ 149,267	$ 197,577	$ 161,152
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of property, equipment, and intangibles	283,948	268,549	237,936
Amortization of debt issuance costs, original issue discount, and other	1,333	5,937	10,407
Gain on disposal of property and equipment, less write-off of totaled tractors	(15,854)	(30,195)	(23,236)
Gain on sale of real property	0	0	(3,018)
Impairments	807	1,480	2,308
Deferred income taxes	(36,079)	26,476	(3,980)
Provision (Reduction)	(1,147)	8,004	2,844
Non-cash loss on debt extinguishment and write-offs of deferred financing costs and original issue discount	0	9,567	11,994
Stock-based compensation expense	6,017	6,525	5,396
Excess tax benefit from stock-based compensation	(2,575)	(2,147)	(3,730)
Income effect of mark-to-market adjustment of interest rate swaps	0	87	(155)
Increase (decrease) in cash resulting from changes in:
Accounts receivable	14,975	48,574	(63,407)
Inventories and supplies	1,796	566	(562)
Prepaid expenses and other current assets	20,999	17,741	17,802
Other assets	1,171	7,785	14,745
Accounts payable, and accrued and other liabilities	41,654	2,972	29,285
Net cash provided by operating activities	466,312	569,498	395,781
Cash flows from investing activities:
(Increase) decrease in cash and cash equivalents — restricted	(1,805)	(9,620)	5,212
Proceeds from maturities of investments	30,269	33,015	29,783
Purchases of investments	(30,061)	(31,930)	(28,921)
Proceeds from sale of property and equipment	113,410	116,330	133,020
Capital expenditures	(239,446)	(342,615)	(305,966)
Payments received on notes receivable	10,114	4,252	5,481
Expenditures on assets held for sale	(31,027)	(25,937)	(4,053)
Payments received on assets held for sale	25,939	14,410	25,326
Payments received on equipment sale receivables	0	288	368
Net cash used in investing activities	(122,607)	(241,807)	(139,750)
Cash flows from financing activities:
Repayment of long-term debt and capital leases	(246,829)	(979,816)	(1,224,628)
Proceeds from long-term debt	0	684,504	900,000
Net (repayments) borrowings on revolving line of credit	(70,000)	143,000	40,000
Borrowings under accounts receivable securitization	105,000	75,000	119,000
Repayment of accounts receivable securitization	(50,000)	(184,000)	(49,000)
Payment of deferred loan costs	0	(4,235)	(11,783)
Proceeds from common stock issued	14,469	8,167	12,604
Repurchase of Class A common stock	(117,119)	(70,000)	0
Excess tax benefits from stock-based compensation	2,575	2,147	3,730
Net cash used in financing activities	(361,904)	(325,233)	(210,077)
Net (decrease) increase in cash and cash equivalents	(18,199)	2,458	45,954
Cash and cash equivalents at beginning of period	107,590	105,132	59,178
Cash and cash equivalents at end of period	89,391	107,590	105,132
Cash paid during the period for:
Interest	29,150	45,390	89,341
Income taxes	79,250	78,522	82,776
Non-cash investing activities:
Equipment purchase accrual	11,103	447	35,831
Notes receivable from sale of assets	4,158	7,670	5,431
Equipment sales receivables	0	0	288
Non-cash financing activities:
Capital lease additions	12,811	145,338	101,581
Accrued deferred loan costs	0	105	177
Insurance premium notes payable	$ 8,430	$ 7,658	$ 37