CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Receivables, allowance for doubtful accounts	$ 44,364	$ 39,543
Preferred stock, par value (in dollars per share)	$ 0.10	$ 0.10
Preferred stock, shares authorized (shares)	20,000,000	20,000,000
Preferred stock, shares issued (shares)	0	0
Preferred stock, shares outstanding (shares)	0	0
Common stock, par value (in dollars per share)	$ 0.10	$ 0.10
Common stock, shares authorized (shares)	480,000,000	480,000,000
Common stock, shares issued (shares)	179,003,000	179,006,000
Common stock shares outstanding (shares)	139,871,000	141,258,000
Treasury stock (shares)	39,132,000	37,748,000