CONDENSED CONSOLIDATED BALANCE SHEETS (PARENTHETICALS) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 32,174	$ 26,690
Cumulative preferred stock, par value (in dollars per share)	$ 5	$ 5
Cumulative preferred stock, shares authorized (in shares)	12,000,000	12,000,000
Cumulative preferred stock, shares issued (in shares)	0	0
Cumulative preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.50	$ 0.50
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares issued (in shares)	109,659,219	109,659,219
Treasury stock, shares at cost (in shares)	51,968,546	50,854,905