Cash and Investments - Cash, Cash Equivalents, Short-Term Investments, and Restricted Cash (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Investment Holdings [Line Items]
Cash	$ 2,042	$ 2,763
Cash equivalents:
Total cash equivalents	9,924	10,364
Total cash and cash equivalents	11,966	13,127	$ 11,102	$ 13,510
Short-term investments:
Total short-term investments	17,464	13,263
Restricted cash—money market fund	250	250
Total cash, cash equivalents, short-term investments and restricted cash	29,680	26,640
Corporate debt securities [Member]
Cash equivalents:
Total cash equivalents	250	1,002
Short-term investments:
Total short-term investments	16,065	12,713
Corporate commercial paper [Member]
Short-term investments:
Total short-term investments	1,399	550
Money market funds [Member]
Cash equivalents:
Total cash equivalents	$ 9,674	$ 9,362