Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
OPERATING ACTIVITIES
Net income	$ 63,289	$ 54,740
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	79,796	47,609
Deferred income taxes	15,342	5,325
Amortization of stock-based compensation	688	806
Gain on disposal of property and equipment	(27,160)	(24,299)
Changes in certain working capital items:
Trade receivables	(2,835)	(1,557)
Prepaid expenses and other current assets	(825)	(2,439)
Accounts payable, accrued liabilities, and accrued expenses	(4,851)	(1,810)
Accrued income taxes	5,573	(5,182)
Net cash provided by operating activities	129,017	73,193
INVESTING ACTIVITIES
Proceeds from sale of property and equipment	64,436	56,751
Purchases of property and equipment, net of trades	(121,088)	(91,845)
Maturity, calls and sales of investments	0	9,875
Acquisition of business, net of cash acquired	(3,011)	0
Change in other assets	(6,277)	(195)
Net cash used in investing activities	(65,940)	(25,414)
FINANCING ACTIVITIES
Payments of Ordinary Dividends, Common Stock	(3,517)	(3,402)
Proceeds from Lines of Credit	3,000	0
Repayments on line of credit	(57,000)	0
Net cash used in financing activities	(57,517)	(3,402)
Net increase in cash and cash equivalents	5,560	44,377
CASH AND CASH EQUIVALENTS
Beginning of period	17,763	119,838
End of period	23,323	164,215
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Interest paid	417	0
Cash paid during the period for income taxes, net of refunds	13,196	31,076
Noncash investing and financing activities:
Fair value of revenue equipment traded	3,335	0
Purchased property and equipment in accounts payable	21,869	19,051
Common stock dividends declared in accounts payable	$ 1,758	$ 1,700