Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
OPERATING ACTIVITIES
Net income	$ 70,582	$ 61,541	$ 69,932
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	69,649	57,821	57,876
Deferred income taxes	10,262	(5,751)	14,743
Loss on sale of investments	200	0	0
Amortization of stock-based compensation	1,184	2,379	150
Gain on disposal of property and equipment	(33,270)	(15,109)	(32,133)
Changes in certain working capital items:
Trade receivables	7,834	(2,357)	(2,579)
Prepaid expenses and other current assets	904	5,688	(6,459)
Accounts payable, accrued liabilities, and accrued expenses	(9,722)	953	(952)
Accrued income taxes	(6,388)	(2,992)	(1,498)
Net cash provided by operating activities	111,235	102,173	99,080
INVESTING ACTIVITIES
Proceeds from sale of property and equipment	92,313	29,184	73,018
Purchases of property and equipment, net of trades	(135,195)	(66,811)	(126,257)
Maturity and calls of investments	21,100	32,350	38,125
Purchases of investments	(110,900)	0	0
Change in other assets	(825)	(704)	(1,818)
Net cash (used in) provided by investing activities	(133,507)	(5,981)	(16,932)
FINANCING ACTIVITIES
Cash dividends	(6,861)	(91,934)	(7,148)
Proceeds from Issuance of Long-term Debt	75,000	0	0
Repayment of long-term debt	(147,942)	0	0
Repurchases of common stock	0	(24,190)	(56,350)
Net cash used in financing activities	(79,803)	(116,124)	(63,498)
Net (decrease) increase in cash and cash equivalents	(102,075)	(19,932)	18,650
CASH AND CASH EQUIVALENTS
Beginning of period	119,838	139,770	121,120
End of period	17,763	119,838	139,770
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Interest Paid	4	0	0
Cash paid during the period for income taxes, net of refunds	38,101	42,776	24,152
Noncash investing and financing activities:
Fair value of revenue equipment traded	2,138	0	0
Purchased property and equipment in accounts payable	11,191	698	1,683
Issuance of common stock in acquisition of business	$ 41,100	$ 0	$ 0