Cash and Investments - Cash, Cash Equivalents, Short-Term Investments, and Restricted Cash (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Investment Holdings [Line Items]
Cash	$ 1,872	$ 2,763
Cash equivalents:
Total cash equivalents	11,513	10,364
Total cash and cash equivalents	13,385	13,127	$ 12,575	$ 13,510
Short-term investments:
Total short-term investments	15,926	13,263
Restricted cash—money market fund	250	250
Total cash, cash equivalents, short-term investments and restricted cash	29,561	26,640
Corporate commercial paper [Member]
Cash equivalents:
Total cash equivalents	1,000
Short-term investments:
Total short-term investments	2,496	550
Corporate debt securities [Member]
Cash equivalents:
Total cash equivalents	321	1,002
Short-term investments:
Total short-term investments	13,430	12,713
Money market funds [Member]
Cash equivalents:
Total cash equivalents	$ 10,192	$ 9,362