Geographic and Segment Information - Net Sales by Region, Based on Location of Customer (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	$ 164,885	$ 164,164
Korea [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	62,470	67,013
Asia Pacific (other than Korea) [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	79,177	70,221
U.S.A. [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	19,370	19,753
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	3,653	6,893
Others [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	$ 215	$ 284