Income Taxes - Summary of Composition of Net Deferred Income Tax Assets (Liabilities) (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets
Inventory reserves	$ 1,630	$ 1,822
Derivative assets		110
Derivative liabilities	(1,253)
Accrued expenses	2,826	2,803
Product warranties	52	113
Other reserves	356	372
Property, plant and equipment	9,759	13,314
Intangible assets	35	103
Accumulated severance benefits	36,245	31,478
Foreign currency translation losses	20,067	53,130
NOL carry-forwards	175,543	167,590
Tax credit	20,583	20,249
Other long-term payable	1,801	2,079
Others	3,546	4,885
Total deferred tax assets	271,190	298,048
Less: Valuation allowance	(251,132)	(281,473)	$ (279,867)	$ (194,739)
Deferred tax assets, net	20,058	16,575
Deferred tax liabilities
Foreign currency translation gains	18,187	14,338
Prepaid expense	1,464	1,644
Others	143	410
Total deferred tax liabilities	19,794	16,392
Net deferred tax assets	264	183	171
Reported as
Current deferred income tax assets		37
Non-current deferred income tax assets	264	193
Current deferred income tax liabilities		(46)
Non-current deferred income tax liabilities		(1)
Net deferred tax assets	$ 264	$ 183	$ 171