Consolidated Condensed Balance Sheets (Unaudited) (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Assets:
Accumulated depreciation on revenue earning equipment	$ 3,606,141	$ 3,596,102
Accumulated depreciation on operating property and equipment	1,015,764	991,117
Allowance for doubtful accounts, current	$ 17,322	$ 16,955
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	53,067,722	53,335,386