Geographic and Segment Information - Net Sales by Region, Based on Location of Products are Billed (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	$ 167,106	$ 162,015	$ 315,211	$ 326,900
Korea [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	46,822	61,755	97,450	124,225
Asia Pacific (Other Than Korea) [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	100,107	75,582	181,900	154,759
U.S.A. [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	8,338	20,310	13,114	39,680
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	11,749	3,708	22,266	7,361
Others [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	$ 90	$ 660	$ 481	$ 875