Summary of Cash, Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	$ 23,483	$ 24,426
Unrealized Gains		1
Fair Value	23,483	24,427
Cash and money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	14,806	16,211
Fair Value	14,806	16,211
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Gains		1
Amortized Cost	8,677	8,215
Fair Value	$ 8,677	$ 8,216