Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
OPERATING ACTIVITIES
Net income	$ 40,551	$ 38,874
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	51,779	32,326
Deferred income taxes	10,103	4,710
Amortization of stock-based compensation	546	622
Gain on disposal of property and equipment	(15,903)	(19,823)
Changes in certain working capital items:
Trade receivables	(3,758)	(3,047)
Prepaid expenses and other current assets	(2,237)	(3,524)
Accounts payable, accrued liabilities, and accrued expenses	(6,979)	1,244
Accrued income taxes	4,046	(1,049)
Net cash provided by operating activities	78,148	50,333
INVESTING ACTIVITIES
Proceeds from sale of property and equipment	29,432	40,404
Purchases of property and equipment, net of trades	(72,384)	(77,156)
Maturity, calls and sales of investments	0	9,825
Acquisition of business, net of cash acquired	(3,011)	0
Change in other assets	(49)	11
Net cash used in investing activities	(46,012)	(26,916)
FINANCING ACTIVITIES
Payments of Ordinary Dividends, Common Stock	(1,757)	(1,701)
Proceeds from Lines of Credit	3,000	0
Repayments on line of credit	(35,000)	0
Net cash used in financing activities	(33,757)	(1,701)
Net (decrease) increase in cash and cash equivalents	(1,621)	21,716
CASH AND CASH EQUIVALENTS
Beginning of period	17,763	119,838
End of period	16,142	141,554
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Interest paid	306	0
Cash paid during the period for income taxes, net of refunds	6,486	17,301
Noncash investing and financing activities:
Fair value of revenue equipment traded	3,335	0
Purchased property and equipment in accounts payable	28,406	214
Common stock dividends declared in accounts payable	$ 1,759	$ 1,701