CONDENSED CONSOLIDATED BALANCE SHEETS (PARENTHETICAL) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 28,208	$ 26,690
Cumulative preferred stock, par value (in dollars per share)	$ 5	$ 5
Cumulative preferred stock, shares authorized	12,000,000	12,000,000
Cumulative preferred stock, shares issued	0	0
Cumulative preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.5	$ 0.5
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	109,659,219	109,659,219
Treasury stock, shares at cost	51,253,521	50,854,905