Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Allowance of accounts receivable	$ 3,991	$ 3,222
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	50,000	50,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	50,000,000	50,000,000
Common stock, shares issued	25,551,617	25,322,701
Common stock, shares outstanding	25,551,617	25,322,701
Deferred compensation trust	170,310	166,807