Consolidated Condensed Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Assets:
Allowance for doubtful accounts, current	$ 16,138	$ 15,560
Finite-Lived Intangible Assets, Accumulated Amortization	48,691	45,736
Operating property and equipment, accumulated depreciation	$ 1,105,458	$ 1,083,604
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)	53,478,452	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