Consolidated Condensed Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Assets:
Allowance for doubtful accounts, current	$ 16,137	$ 15,372
Finite-Lived Intangible Assets, Accumulated Amortization	47,215	45,736
Revenue earning equipment, accumulated depreciation	4,049,623	3,963,555
Operating property and equipment, accumulated depreciation	$ 1,095,352	$ 1,046,137
Shareholders’ equity:
Common stock, par value (in dollars per share)	$ 0.50	$ 0.50
Common stock, shares authorized (in shares)	400,000,000	400,000,000
Common stock, shares outstanding (in shares)	53,703,407	53,490,603
Preferred stock, par value (in dollars per share)	$ 0	$ 0
Preferred stock, shares authorized (in shares)	3,800,917	3,800,917
Preferred stock, shares outstanding (in shares)	0	0