Registered Offering and Warrants - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended				9 Months Ended
	Mar. 17, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2020
Class Of Stock [Line Items]
Sale price		$ 5.95				$ 5.95
Warrants to purchase		19,000,000				19,000,000
Warrant exercise price		$ 5.95				$ 5.95
Shares issued for common stock at-the-market, net of issuance costs	$ 90,439	$ 45,230	$ 3,842	$ 27,027	$ 37,445
Issuance costs incurred on registered offering	$ 5,150
Daily cash penalty	1.00%
Level 3 [Member]
Class Of Stock [Line Items]
Estimated fair value of warrant liability per warrant		$ 3.76				3.76
Other Expense (Income) [Member]
Class Of Stock [Line Items]
Issuance costs incurred on registered offering	$ 3,953
Pre funded Warrants [Member]
Class Of Stock [Line Items]
Warrant exercise price		$ 0.0001				$ 0.0001
Warrant Liability [Member]
Class Of Stock [Line Items]
Shares issued for common stock at-the-market, net of issuance costs	$ 69,414
Class 2 Common Stock [Member]
Class Of Stock [Line Items]
Shares issued for common stock at-the-market, net of issuance costs, shares	7,250,000	6,781,090				9,493,494
Sale price	$ 4.76
Warrants to purchase	19,000,000
Warrant exercise price	$ 5.95
Shares issued for common stock at-the-market, net of issuance costs	$ 21,025
Issuance costs incurred on registered offering	$ 1,197					$ 1,540
Class 2 Common Stock [Member] | Minimum [Member]
Class Of Stock [Line Items]
Warrants expire period	6 months
Class 2 Common Stock [Member] | Maximum [Member]
Class Of Stock [Line Items]
Warrants expire period	5 years
Class 2 Common Stock [Member] | Pre funded Warrants [Member]
Class Of Stock [Line Items]
Sale price	$ 4.7599
Warrants to purchase	11,750,000			11,750,000
Warrant exercise price	$ 0.0001			$ 0.0001