Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Statement of Financial Position [Abstract]
Accumulated depreciation on revenue earning equipment	$ 3,514,910	$ 3,462,359
Accumulated depreciation on operating property and equipment	$ 966,220	$ 911,717
Preferred stock, par value	$ 0	$ 0
Preferred stock, shares authorized	3,800,917	3,800,917
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.50	$ 0.50
Common stock, shares authorized	400,000,000	400,000,000
Common stock, shares outstanding	51,371,696	51,143,946