Annual report pursuant to Section 13 and 15(d)

Intangible Assets - Additional Information (Detail)

v3.8.0.1
Intangible Assets - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Goodwill And Intangible Assets Disclosure [Abstract]      
Amortization expenses of intangible assets $ 1,826 $ 1,927 $ 1,640