Cash and Investments - Cash, Cash Equivalents, Short-Term Investments, and Restricted Cash (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
Investment Holdings [Line Items]
Cash	$ 2,718	$ 2,521
Cash equivalents:
Total cash equivalents	9,857	10,989
Total cash and cash equivalents	12,575	13,510	13,236	9,903
Short-term investments:
Total short-term investments	12,646	7,295
Restricted cash—money market fund	250	250
Total cash, cash equivalents, investments and restricted cash	25,471	21,055
Corporate commercial paper [Member]
Cash equivalents:
Total cash equivalents	1,250
Short-term investments:
Total short-term investments	1,199	1,500
Corporate debt securities [Member]
Cash equivalents:
Total cash equivalents	251	2,000
Short-term investments:
Total short-term investments	11,447	4,794
Foreign government bonds [Member]
Short-term investments:
Total short-term investments		1,001
Money market funds [Member]
Cash equivalents:
Total cash equivalents	$ 8,356	$ 8,989