Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Receivables, allowance for doubtful accounts	$ 11,332	$ 8,557
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	160,000,000	160,000,000
Common stock, shares issued (in shares)	95,065,638	95,065,638
Common stock, shares outstanding (in shares)	56,593,820	56,299,949
Treasury stock, shares (in shares)	38,471,818	38,765,689