Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
OPERATING ACTIVITIES
Net income	$ 56,041	$ 63,289
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	82,053	79,796
Deferred income taxes	(4,569)	15,342
Amortization of stock-based compensation, net of tax	(1,042)	(688)
Gain on disposal of property and equipment	(27,250)	(27,160)
Changes in certain working capital items:
Trade receivables	12,515	(2,835)
Prepaid expenses and other current assets	3,337	(825)
Accounts payable, accrued liabilities, and accrued expenses	7,001	(4,851)
Accrued income taxes	12,777	5,573
Net cash provided by operating activities	142,947	129,017
INVESTING ACTIVITIES
Proceeds from sale of property and equipment	89,073	64,436
Purchases of property and equipment, net of trades	(111,688)	(121,088)
Acquisition of business, net of cash acquired	0	(3,011)
Change in designated funds for equipment purchases	(12,488)	(5,824)
Change in other assets	1,495	(453)
Net cash used in investing activities	(33,608)	(65,940)
FINANCING ACTIVITIES
Payments of Ordinary Dividends, Common Stock	(5,254)	(3,517)
Contingent consideration related to acquisition	(1,765)	0
Proceeds from Lines of Credit	0	3,000
Repayments on line of credit	(24,600)	(57,000)
Repurchases of common stock	(30,858)
Net cash used in financing activities	(62,477)	(57,517)
Net increase (decrease) in cash and cash equivalents	46,862	5,560
CASH AND CASH EQUIVALENTS
Beginning of period	17,303	17,763
End of period	64,165	23,323
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Interest paid	40	417
Cash paid during the period for income taxes, net of refunds	24,562	13,196
Noncash investing and financing activities:
Fair value of revenue equipment traded	0	3,335
Purchased property and equipment in accounts payable	10,956	21,869
Sold property and equipment in other current assets	12,488	0
Treasury stock acquired in accounts payable	4,911	0
Common stock dividends declared in accounts payable	$ 0	$ 1,758