Business - Additional Information (Detail) - USD ($)	1 Months Ended		6 Months Ended
	Aug. 31, 2021	Aug. 06, 2021	Jun. 30, 2021	Jul. 31, 2021	Dec. 31, 2020
Cash and cash equivalents			$ 76,746,000		$ 115,069,000
Accumulated deficit			$ 808,325,000		$ 764,101,000
Common Stock, Shares Authorized			350,000,000		350,000,000
Common Stock, Shares, Outstanding			215,559,148		214,591,906
Description of payment terms			The term loan amortization date is April 1, 2022; provided, however, if the Company raises $50M in funding on or prior to March 31, 2022, the term loan first payment date shall automatically be extended to September 1, 2022. Further, if the Company raised $50M on or prior to March 31, 2022 and an additional $50M on or prior to August 31, 2022, the term loan amortization shall automatically be extended to September 1, 2023. The term loan maturity date is March 1, 2023; provided, however, if Company achieves the funding milestones, the term loan maturity date shall automatically be extended to August 1, 2025. There is a final payment due of 5.75%.
Common Stock [Member]
Common Stock, Shares Authorized			50,000,000
Common Stock, Shares, Outstanding				215,559,148
Common stock reserved for future issuance				34,088,731
Forecast [Member]
Gross proceeds from debt	$ 25,000,000.0
Forecast [Member] | Warrants [Member]
Warrant exercise per share		$ 2.22
Warrants granted to purchase shares of closing		432,843
Warrant granted to draw tranche		$ 25,000.0
Forecast [Member] | Term Loan [Member]
Initial term loan		25,000,000.0
Additonal tranche facility		$ 25,000,000.0
Debt Instrument, maturity date		Mar. 01, 2023
Term loan maturity date, extended		Aug. 01, 2025
Term loan, amortization date		Apr. 01, 2022
Term loan amortization date, extended		Sep. 01, 2023
Percentage of final payment due		5.75%
Raise fund		$ 50,000
Forecast [Member] | Term Loan [Member] | Prime Rate [Member]
Interest rate		4.50%
Forecast [Member] | Term Loan [Member] | Maximum [Member]
Interest rate		7.75%