CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Customer receivables, net of allowance for doubtful accounts of $4,039 and $8,059, respectively	$ 4,039	$ 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	65,460,014	64,741,648
Common stock, shares outstanding	49,339,552	49,096,290
Non-vesting restricted shares	841,610	993,962
Treasury shares	16,120,462	15,645,358