Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Allowance for doubtful accounts	$ 8,701	$ 7,988
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	95,000,000	95,000,000
Common stock, shares issued	47,854,510	47,443,716
Common stock, shares outstanding	47,854,510	47,443,716
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Treasury Stock, shares	0	0
Series A Preferred Stock [Member]
Preferred stock, shares authorized	6,000	6,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Series B Preferred Stock [Member]
Preferred stock, shares authorized	20,000	20,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0