Shareholders' Equity - Additional Information (Detail) - USD ($)							3 Months Ended			9 Months Ended
		Aug. 13, 2021	Jul. 06, 2021	Jul. 02, 2021	Mar. 15, 2021	Jun. 28, 2018	Jun. 30, 2021	Mar. 31, 2021		Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Apr. 28, 2017
Class Of Warrant Or Right [Line Items]
Common stock, par value										$ 0.001		$ 0.001
Net proceeds after deducting underwriting discounts commissions and offering expenses										$ 122,148,000
Issuance of common stock and pre-funded warrants in public offering, net of offering costs							$ 321,000	$ 121,827,000	[1]
H.C. Wainwright & Co., LLC [Member]
Class Of Warrant Or Right [Line Items]
Common stock, shares sold										0	942,825
Common stock, par value													$ 0.001
Termination of agreement				July 12, 2021
Net proceeds from sale of shares											$ 2,300,000
H.C. Wainwright & Co., LLC [Member] | Maximum [Member]
Class Of Warrant Or Right [Line Items]
Amount available to sell under equity program													$ 60,000
Evercore Group L.L.C., [Member]
Class Of Warrant Or Right [Line Items]
Common stock, shares sold										0
Common stock, par value			$ 0.001
Sales commissions in fixed percentage of gross proceeds per share			3.00%
Common stock sales agreement, effective date			Jul. 16, 2021
Evercore Group L.L.C., [Member] | Maximum [Member]
Class Of Warrant Or Right [Line Items]
Amount available to sell under equity program			$ 60,000,000
Warrant Repurchase [Member]
Class Of Warrant Or Right [Line Items]
Common stock, par value										$ 0.15
Warrants and rights outstanding										$ 3,900,000
Warrant Repurchase [Member] | Milestone Warrants [Member]
Class Of Warrant Or Right [Line Items]
Warrant to purchase of common stock										26,061,769
Number of warrants expired		3,474,902
Common Stock [Member]
Class Of Warrant Or Right [Line Items]
Issuance of common stock and pre-funded warrants in public offering, net of offering costs	[1]							$ 57,000
Common Stock [Member] | H.C. Wainwright & Co., LLC [Member]
Class Of Warrant Or Right [Line Items]
Issuance of common stock and pre-funded warrants in public offering, net of offering costs						$ 2,300,000
Public Offering of Common Stock [Member]
Class Of Warrant Or Right [Line Items]
Common stock, shares sold					57,479,978
Common stock, par value					$ 0.001
Common stock, sale of stock, price per share					$ 1.45
Common stock, shares issued to underwriters					11,694,150
Common stock, pre-funded warrants to purchase					32,175,172
Common Stock pre funded warrants exercise price					$ 0.001
Common Stock pre funded warrants per warrant					$ 1.449
Net proceeds after deducting underwriting discounts commissions and offering expenses					$ 122,100,000

[1] As discussed in Note 10. Stockholders’ Equity, the Company sold (i) an aggregate of 57,479,978 shares of the Company’s common stock, par value $0.001 per share and (ii) pre-funded warrants to purchase an aggregate of 32,175,172 shares of the Company's common stock at an exercise price, equal to the par value, of $0.001 per share.