Cash, Cash Equivalents and Investments - Cash, Cash Equivalents and Short-Term Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Investment Holdings [Line Items]
Cash	$ 11,470	$ 7,270
Cash equivalents:
Total cash equivalents	876	9,173
Total cash and cash equivalents	12,346	16,443	$ 13,385	$ 13,127
Short-term investments:
Total short-term investments	19,231	13,280
Restricted cash equivalents—money market fund		250
Total cash, cash equivalents and short-term investments	31,577	29,973
Corporate commercial paper [Member]
Cash equivalents:
Total cash equivalents		5,404
Short-term investments:
Total short-term investments	13,701	6,245
Corporate debt securities [Member]
Cash equivalents:
Total cash equivalents		2,269
Short-term investments:
Total short-term investments	5,530	6,028
Treasury bonds [Member]
Short-term investments:
Total short-term investments		1,007
Money market funds [Member]
Cash equivalents:
Total cash equivalents	$ 876	$ 1,500