Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Assets
Cash and cash equivalents	$ 484,502	$ 429,784
Marketable securities	0	3,200
Trade accounts receivable, net	575,013	567,097
Other accounts receivable	51,063	43,912
Operating supplies, at lower of average cost or market	23,910	23,180
Prepaid expenses and other current assets	57,961	49,681
Deferred income taxes	15,332	34,520
Total Current Assets	1,207,781	1,151,374
Property, Plant and Equipment [Abstract]
Land	193,364	195,737
Buildings and leasehold improvements	856,038	840,966
Revenue equipment	1,857,737	1,746,816
Other equipment	353,205	329,730
Total Property, Plant and Equipment	3,260,344	3,113,249
Accumulated depreciation	(1,603,511)	(1,526,648)
Net Property, Plant and Equipment	1,656,833	1,586,601
Other Assets
Deferred charges and other assets	32,200	33,963
Capitalized software, net	21,488	20,365
Employee benefits	15,018	10,951
Intangible assets, net	8,640	10,997
Goodwill	337,971	338,164
Total Noncurrent Assets	415,317	414,440
Total Assets	3,279,931	3,152,415
Liabilities and Shareholders' Equity
Accounts payable	390,537	330,665
Accrued liabilities	229,078	253,209
Self-insurance accruals	105,063	100,828
Short-term borrowings	1,588	6,982
Current maturities of long-term debt and capital leases	19,685	16,008
Total Current Liabilities	745,951	707,692
Long-Term Liabilities
Long-term debt	719,155	719,016
Long-term obligations under capital leases	16,185	30,355
Self-insurance accruals	142,307	143,735
Employee benefits	240,171	603,619
Other liabilities and deferred credits	39,524	32,201
Deferred income taxes	237,949	77,412
Total Liabilities	2,141,242	2,314,030
Commitments and Contingencies (Notes 5, 6, 7 and 11)
Shareholders' Equity
Common stock, $0.625 par value; authorized 100,000,000 shares; issued 64,592,756 and 63,565,453 shares, respectively	40,349	39,701
Additional paid-in capital, common stock	653,487	614,334
Retained earnings	1,043,472	966,939
Cost of repurchased common stock (7,669,889 and 7,583,471 shares, respectively)	(329,088)	(326,128)
Accumulated Other Comprehensive Loss	(269,531)	(456,461)
Total Shareholders' Equity	1,138,689	838,385
Total Liabilities and Shareholders' Equity	$ 3,279,931	$ 3,152,415