CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 6,108	$ 8,059
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	65,434,707	64,741,648
Common stock, shares outstanding	49,321,826	49,096,290
Non-vesting restricted shares	853,360	993,962
Treasury shares	16,112,881	15,645,358