Consolidated Statements of Comprehensive Income (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating Revenue	$ 545,745	$ 528,623	$ 499,516
Operating Expenses
Salaries, wages, and benefits	167,073	166,717	167,980
Rent and purchased transportation	6,273	7,527	9,460
Fuel	168,981	161,915	126,477
Operations and maintenance	25,282	20,938	17,086
Operating taxes and licenses	8,694	9,225	8,480
Insurance and claims	14,906	13,142	12,526
Communications and utilities	2,953	2,957	3,187
Depreciation	57,158	57,226	61,949
Other operating expenses	14,633	14,552	14,239
Gain on disposal of property and equipment	(15,109)	(32,133)	(13,317)
Total operating expenses	450,844	422,066	408,067
Operating income	94,901	106,557	91,449
Interest income	674	773	1,424
Income before income taxes	95,575	107,330	92,873
Federal and state income taxes	34,034	37,398	30,657
Net income	61,541	69,932	62,216
Other comprehensive income, net of tax	1,797	0	2,245
Comprehensive income	$ 63,338	$ 69,932	$ 64,461
Net income per share
Basic	$ 0.72	$ 0.78	$ 0.69
Diluted	$ 0.71	$ 0.78	$ 0.69
Weighted average shares outstanding
Basic	85,892	89,656	90,689
Diluted	86,201	89,673	90,689
Dividends declared per share	$ 1.08	$ 0.08	$ 1.08