Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
OPERATING ACTIVITIES
Net income	$ 40,928	$ 40,551
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	53,375	51,779
Deferred income taxes	(2,063)	10,103
Amortization of stock-based compensation, net of tax	(714)	(546)
Gain on disposal of property and equipment	(19,849)	(15,903)
Changes in certain working capital items:
Trade receivables	6,574	(3,758)
Prepaid expenses and other current assets	1,368	(2,237)
Accounts payable, accrued liabilities, and accrued expenses	6,441	(6,979)
Accrued income taxes	14,222	4,046
Net cash provided by operating activities	101,710	78,148
INVESTING ACTIVITIES
Proceeds from sale of property and equipment	57,349	29,432
Purchases of property and equipment, net of trades	(64,703)	(72,384)
Acquisition of business, net of cash acquired	0	(3,011)
Change in designated funds for equipment purchases	(5,741)	0
Change in other assets	1,682	(49)
Net cash used in investing activities	(11,413)	(46,012)
FINANCING ACTIVITIES
Payments of Ordinary Dividends, Common Stock	(1,759)	(1,757)
Contingent consideration related to acquisition	(1,765)	0
Proceeds from Lines of Credit	0	3,000
Repayments on line of credit	(24,600)	(35,000)
Net cash used in financing activities	(28,124)	(33,757)
Net increase (decrease) in cash and cash equivalents	62,173	(1,621)
CASH AND CASH EQUIVALENTS
Beginning of period	17,303	17,763
End of period	79,476	16,142
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Interest paid	40	306
Cash paid during the period for income taxes, net of refunds	10,802	6,486
Noncash investing and financing activities:
Fair value of revenue equipment traded	0	3,335
Purchased property and equipment in accounts payable	5,682	28,406
Sold property and equipment in other current assets	1,598	0
Common stock dividends declared in accounts payable	$ 1,760	$ 1,759