Cash, Cash Equivalents and Investments - Cash, Cash Equivalents and Short-Term Investments (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Investment Holdings [Line Items]
Cash	$ 5,039	$ 11,016
Cash equivalents:
Total cash equivalents	4,429	3,296
Total cash and cash equivalents	9,468	14,312	$ 10,619	$ 16,443
Short-term investments:
Total short-term investments	17,828	18,888
Total cash, cash equivalents and short-term investments	27,296	33,200
Corporate commercial paper [Member]
Cash equivalents:
Total cash equivalents	3,498	500
Short-term investments:
Total short-term investments	10,895	11,465
Corporate debt securities [Member]
Cash equivalents:
Total cash equivalents	750
Short-term investments:
Total short-term investments	6,933	7,423
Money market funds [Member]
Cash equivalents:
Total cash equivalents	$ 181	$ 2,796