CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 4,408	$ 4,039
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)	65,722,418	65,460,014
Common stock, shares outstanding (n shares)	49,500,794	49,339,552
Non-vesting restricted shares (in shares)	893,544	841,610
Treasury shares (in shares)	16,221,624	16,120,462