Cash, Cash Equivalents and Investments - Cash, Cash Equivalents and Short-Term Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Investment Holdings [Line Items]
Cash	$ 8,325	$ 7,270
Cash equivalents:
Total cash equivalents	4,017	9,173
Total cash and cash equivalents	12,342	16,443	$ 9,948	$ 13,127
Short-term investments:
Total short-term investments	15,284	13,280
Restricted cash equivalents—money market fund	250	250
Total cash, cash equivalents and short-term investments	27,876	29,973
Corporate commercial paper [Member]
Cash equivalents:
Total cash equivalents	1,749	5,404
Short-term investments:
Total short-term investments	10,735	6,245
Corporate debt securities [Member]
Cash equivalents:
Total cash equivalents		2,269
Short-term investments:
Total short-term investments	3,541	6,028
Treasury bonds [Member]
Short-term investments:
Total short-term investments	1,008	1,007
Money market funds [Member]
Cash equivalents:
Total cash equivalents	$ 2,268	$ 1,500