Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 2,852	$ 3,477	$ 3,534
Property and equipment, accumulated depreciation	(51,099)	(45,766)	(43,202)
Intangible assets, accumulated amortization	$ 20,656	$ 16,344	$ 11,390
Preferred stock, par value	$ 0.01	$ 0.01	$ 0.01
Preferred stock, shares authorized	1,000,000	1,000,000	1,000,000
Preferred stock, shares issued	0	0	0
Common stock, par value	$ 0.01	$ 0.01	$ 0.01
Common stock, shares authorized	30,000,000	30,000,000	30,000,000
Common stock, shares issued	18,787,816	18,420,914	17,336,314
Common stock, shares outstanding	17,128,825	16,761,923	15,677,323
Treasury stock, shares outstanding	1,658,991	1,658,991	1,658,991