Accrued Severance Benefits - Changes in Accrued Severance Benefits (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Postemployment Benefits [Abstract]
Beginning balance	$ 51,785	$ 53,202	$ 53,344	$ 55,691
Provisions	2,167	1,851	5,941	4,494
Severance payments	(1,295)	(1,017)	(4,749)	(4,312)
Translation adjustments	1,204	(2,180)	(675)	(4,017)
Ending balance	53,861	51,856	53,861	51,856
Less: Cumulative contributions to severance insurance deposit accounts	(1,616)	(1,357)	(1,616)	(1,357)
The National Pension Fund	(73)	(80)	(73)	(80)
Group severance insurance plan	(219)	(227)	(219)	(227)
Accrued severance benefits, net	$ 51,953	$ 50,192	$ 51,953	$ 50,192	$ 51,181