Segment Information - Summary of Revenue by Geographic Region (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]
Revenue	$ 8,910	$ 14,268
China [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	3,351	6,450
Taiwan [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	1,701	3,764
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	1,523	1,370
Korea [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	725	1,896
Other [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 1,610	$ 788