Notes Payable - Additional Information (Detail) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Apr. 15, 2019
Debt Instrument [Line Items]
Loss on extinguishment of debt				$ 971,000
Interest expense			$ 472,000	1,527,000	$ 472,000
Loan Agreement [Member]
Debt Instrument [Line Items]
Interest expense	$ 0		$ 0	$ 1,500,000	$ 0
Term Loan [Member] | Loan Agreement [Member] | Hercules Capital, Inc [Member]
Debt Instrument [Line Items]
Aggregate principal amount of loan						$ 15,000,000
Debt discount discount and issuance costs						400,000
Payments of fee						300,000
Payoff amount						16,000,000
Prepayment penalty						200,000
Prepayment fee						$ 800,000
Loss on extinguishment of debt		$ 1,000,000