Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Allowance for doubtful accounts	$ 4,343	$ 4,085
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	150,000,000	150,000,000
Common stock, shares issued (in shares)	62,579,299	62,071,144
Treasury stock, at cost (in shares)	8,765,055	8,206,683