Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Allowance for doubtful accounts	$ 9,850	$ 8,701
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	95,000,000	95,000,000
Common stock, shares issued	47,893,150	47,854,510
Common stock, shares outstanding	47,893,150	47,854,510
Preferred stock, par value	$ 0.01	$ 0.01
Series A Preferred Stock [Member]
Preferred stock, shares authorized	6,000	6,000
Series B Preferred Stock [Member]
Preferred stock, shares authorized	20,000	20,000