Cash and Investments - Cash, Cash Equivalents, Short-Term Investments, and Restricted Cash (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investment Holdings [Line Items]
Cash	$ 11,016	$ 7,270
Cash equivalents:
Total cash and cash equivalents	14,312	16,443	$ 13,127
Short-term investments:
Total short-term investments	18,888	13,280
Restricted cash equivalents		250
Total cash, cash equivalents, short-term investments and restricted cash equivalents	33,200	29,973
Corporate commercial paper [Member]
Cash equivalents:
Cash equivalents	500	5,404
Short-term investments:
Total short-term investments	11,465	6,245
Corporate debt securities [Member]
Cash equivalents:
Cash equivalents		2,269
Short-term investments:
Total short-term investments	7,423	6,028
Treasury bonds [Member]
Short-term investments:
Total short-term investments		1,007
Money market funds [Member]
Cash equivalents:
Cash equivalents	$ 2,796	$ 1,500