Fair Value of Financial Assets and Liabilities - Schedule of Assets and Liabilities Measured at Fair Value (Detail) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	$ 62,604,000	$ 44,834,000
Fair value of derivative liability	491,000	455,000
Fair Value, Measurements, Recurring | Level 1
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	34,816,000	16,816,000
Fair value of derivative liability	0	0
Fair Value, Measurements, Recurring | Level 2
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	27,788,000	28,018,000
Fair value of derivative liability	0	0
Fair Value, Measurements, Recurring | Level 3
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	0	0
Fair value of derivative liability	491,000	$ 455,000
Measurement Input, Discount Rate
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair value of derivative liability	$ 0.14