Fair Value Measurements - Summary of Changes in Fair Values Level Financial Liabilities Recurring Basis Using Unobservable Inputs (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Reclassification of warrant liabilities to equity			$ 62,175
Changes in fair value	$ 16,200	$ 20,900	16,240	$ 20,926
Fair Value Measurements Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Balance, beginning	56,420		56,420
Issuance of warrants				25,009
Securities issuance obligation				6,446
Changes in fair value			17,725	24,965
Balance, at end		56,420		56,420
Settlement of financial liabilities by securities issuance			(11,970)
Reclassification of warrant liabilities to equity			(62,175)
Series A Warrant [Member] | Fair Value Measurements Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Balance, beginning	32,616		32,616
Issuance of warrants				17,133
Balance, at end		32,616		32,616
Changes in fair value			11,597	15,483
Reclassification to equity			(44,213)
Series B Warrant [Member] | Fair Value Measurements Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Balance, beginning	13,319		13,319
Issuance of warrants				7,876
Balance, at end		13,319		13,319
Changes in fair value			4,643	5,443
Reclassification to equity			(17,962)
Warrant Issuance Obligation [Member] | Fair Value Measurements Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Balance, beginning	3,036		3,036
Securities issuance obligation				1,543
Balance, at end		3,036		3,036
Settlement of financial liabilities by securities issuance			(3,188)
Changes in fair value			152	1,493
Common stock Issuance Obligation [Member] | Fair Value Measurements Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Balance, beginning	$ 7,449		7,449
Securities issuance obligation				4,903
Balance, at end		$ 7,449		7,449
Settlement of financial liabilities by securities issuance			(8,782)
Changes in fair value			$ 1,333	$ 2,546