CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 5,274	$ 8,059
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	65,437,957	64,741,648
Common stock, shares outstanding (n shares)	49,323,826	49,096,290
Non-vesting restricted shares (in shares)	854,110	993,962
Treasury shares (in shares)	16,114,131	15,645,358