Fair Value Measurements of Pension Plan Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 908	$ 743	$ 718
Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	908
TAIWAN, PROVINCE OF CHINA
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	830	743
TAIWAN, PROVINCE OF CHINA | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	830	$ 743
GERMANY
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	78
GERMANY | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 78