Assets and Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands		Sep. 30, 2020		Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value		$ 104,053		$ 76,865
Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	[1]	24,923		15,369
U.S. Government Agency Securities | Short-Term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value		55,042	[2]	51,490	[3]
Federal Agency Securities | Short-Term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	[3]			10,006
Federal Agency Securities | Short-Term and Long-Term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	[2]	24,088
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value		79,965		66,859
Fair Value, Inputs, Level 1 | Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	[1]	24,923		15,369
Fair Value, Inputs, Level 1 | U.S. Government Agency Securities | Short-Term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value		55,042	[2]	51,490	[3]
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value		24,088		10,006
Fair Value, Inputs, Level 2 | Federal Agency Securities | Short-Term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	[3]			$ 10,006
Fair Value, Inputs, Level 2 | Federal Agency Securities | Short-Term and Long-Term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	[2]	$ 24,088

[1] Included in cash and cash equivalents on the accompanying condensed consolidated balance sheets.

[2] Included in short-term investments on the accompanying condensed consolidated balance sheets and classified as available-for-sale debt securities. $1.2 million of Federal agency securities are included in long-term investments on the accompanying condensed consolidated balance sheets due to the maturity being more than 12 months.

[3] Included in short-term investments on the accompanying condensed consolidated balance sheets and classified as available-for-sale debt securities.