CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
CONSOLIDATED BALANCE SHEETS
Accounts receivable, allowance for doubtful accounts (in dollars)	$ 9,944	$ 10,197	$ 9,078	$ 7,920	$ 6,472	$ 5,837	$ 4,971	$ 4,941	$ 4,928	$ 3,844
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01	$ 0.01	$ 0.01	$ 0.01	$ 0.01	$ 0.01
Common stock, shares authorized	60,000,000	60,000,000	60,000,000	60,000,000	60,000,000	60,000,000	60,000,000	60,000,000
Common stock, shares issued	35,540,630	35,537,528	35,527,002	35,486,033	35,158,196	35,062,367	35,062,931	34,953,812
Common stock, shares outstanding	35,399,476	35,396,374	35,385,848	35,344,879	35,017,042	34,921,213	34,921,777	34,812,658
Treasury stock, shares	141,154	141,154	141,154	141,154	141,154	141,154	141,154	141,154