Consolidated Condensed Balance Sheets (Unaudited) (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Assets:
Accumulated depreciation on revenue earning equipment	$ 3,496,545	$ 3,514,910
Accumulated depreciation on operating property and equipment	$ 978,101	$ 966,220
Shareholders' equity:
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	$ 0.5	$ 0.5
Common stock, shares authorized	400,000,000	400,000,000
Common stock, shares outstanding	51,922,227	51,371,696