Consolidated Statements of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Operating Revenue	$ 528,623	$ 499,516	$ 459,539
Operating Expenses
Salaries, wages, and benefits	166,717	167,980	168,716
Rent and purchased transportation	7,527	9,460	11,138
Fuel	161,915	126,477	104,246
Operations and maintenance	20,938	17,086	14,913
Operating taxes and licenses	9,225	8,480	9,286
Insurance and claims	13,142	12,526	16,629
Communications and utilities	2,957	3,187	3,655
Depreciation	57,226	61,949	58,730
Other operating expenses	14,552	14,239	12,970
Gain on disposal of property and equipment	(32,133)	(13,317)	(19,708)
Total operating expenses	422,066	408,067	380,575
Operating income	106,557	91,449	78,964
Interest income	773	1,424	2,338
Income before income taxes	107,330	92,873	81,302
Federal and state income taxes	37,398	30,657	24,353
Net income	$ 69,932	$ 62,216	$ 56,949
Earnings per share
Basic	$ 0.78	$ 0.69	$ 0.62
Diluted	$ 0.78	$ 0.69	$ 0.62
Weighted average shares outstanding
Basic	89,656	90,689	91,131
Diluted	89,673	90,689	91,131
Dividends declared per share	$ 0.08	$ 1.08	$ 0.08