Summary of Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	$ 23,342	$ 34,138
Unrealized Gains	6
Unrealized Losses		(3)
Fair Value	23,348	34,135
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	1,005	4,812
Fair Value	1,005	4,812
Marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	8,246	7,504
Unrealized Gains	6
Unrealized Losses		(3)
Fair Value	8,252	7,501
Cash and money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	14,091	21,822
Fair Value	14,091	21,822
Level 2 | Corporate debt securities | Due within 1 year
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	8,246	6,504
Unrealized Gains	6
Unrealized Losses		(3)
Fair Value	8,252	6,501
Level 2 | Government agency securities | Due within 1 year
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost		1,000
Fair Value		1,000
Cash and Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	15,096	26,634
Fair Value	$ 15,096	$ 26,634