Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Allowance for doubtful accounts	$ 3,487	$ 3,873
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)	62,057,230	61,229,980
Treasury stock, at cost (in shares)	7,156,256	6,729,438