Notes Payable - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Apr. 15, 2019
Debt Instrument [Line Items]
Loss on extinguishment of debt			$ 971,000
Interest expense	$ 1,049,000		1,527,000
Loan Agreement [Member]
Debt Instrument [Line Items]
Interest expense	1,000,000	$ 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