Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Statement of Cash Flows [Abstract]
Net income	$ 37,564	$ 72,766
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of property, equipment and intangibles	105,184	86,486
Amortization of debt issuance costs, and other	15	0
Gain on sale of equipment	(2,465)	(7,451)
Gain from available-for-sale securities	0	(4,494)
Impairments	16,746	0
Deferred income taxes	(9,467)	4,655
Provision for doubtful accounts and notes receivable	831	594
Non-cash compensation expense for issuance of common stock to certain members of the Board of Directors	398	398
Stock-based compensation expense	3,393	3,126
Income from investment in TRP partnerships	(1,660)	(177)
Transportation Resource Partners impairment	56	67
Increase (decrease) in cash resulting from changes in:
Trade receivables and equipment sales receivable	(6,027)	(133)
Other current assets	(215)	5,707
Prepaid expenses	(7,641)	649
Income tax receivable	(23,859)	33,122
Other long-term assets	126	547
Accounts payable	(4,447)	1,869
Accrued liabilities and claims accrual	23,791	(6,040)
Net cash provided by operating activities	132,323	191,691
Cash flows from investing activities:
Decrease (increase) in cash and cash equivalents – restricted	745	(19)
Proceeds from maturities of held-to-maturity investments	2,835	0
Purchases of held-to maturity investments	3,015	0
Proceeds from sale of available-for-sale securities	0	7,403
Proceeds from sale of property and equipment/assets held for sale	29,490	49,972
Purchases of property and equipment	(91,925)	(126,028)
Proceeds from notes receivable	1,826	1,348
Expenditures on assets held for sale	(720)	0
Payments received on equipment sale receivables	1,067	0
Cash payments to Transportation Resource Partners	(1,166)	(21,778)
Cash proceeds from Transportation Resource Partners	9,775	423
Cash and cash equivalents received with 2017 Merger	28,493	0
Net cash used in investing activities	(22,595)	(88,679)
Cash flows from financing activities:
Repayment of long-term debt and capital leases	(454,148)	0
Proceeds from long-term debt	400,000	0
Repayments on Knight Revolver, net	(18,000)	(60,000)
Borrowings on Revolver	85,000	0
Borrowings under accounts receivable securitization	20,000	0
Payment of deferred loan costs	(2,312)	0
Proceeds from exercise of stock options	9,726	9,321
Share withholding for taxes due on equity awards	(6,114)	(1,421)
Payments to repurchase company's common stock	0	(39,873)
Dividends paid	(14,769)	(14,753)
Cash distribution to noncontrolling interest holder	(710)	(1,091)
Net cash provided by (used) in financing activities	18,673	(107,817)
Net increase (decrease) in cash and cash equivalents	128,401	(4,805)
Cash and cash equivalents at beginning of period	8,021	8,691
Cash and cash equivalents at end of period	136,422	3,886
Cash paid during the period for:
Interest	2,924	782
Income taxes	50,709	7,238
Non-cash investing and financing transactions:
Equipment acquired included in accounts payable	16,557	6,436
Equipment sales receivables	954	0
Financing provided to independent contractors for equipment sold	1,801	1,024
Transfer from property and equipment to assets held for sale	26,180	25,035
Capital lease additions	15,020	0
Net dividend accrued for restricted stock units	$ 38	$ 69