Warrants - Summary of Warrant Activity (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Apr. 24, 2019	May 24, 2018	May 25, 2017
Class of Warrant or Right [Line Items]
Number of Warrant Shares, Reserved (in shares)				4,072,308	3,149,231	1,995,385
Weighted Average Exercise Price, Expired (in dollars per share)	$ 38.67
Warrants Not Settleable in Cash
Class of Warrant or Right [Line Items]
Number of Warrant Shares, Outstanding Beginning balance (in shares)		1,012,513
Number of Warrant Shares, Exercised (in shares)	(15,385)	(672,125)
Number of Warrant Shares, Expired (in shares)		(7,354)
Number of Warrant Shares, Reserved (in shares)	1,753,523
Number of Warrant Shares, Outstanding Ending balance (in shares)			1,012,513
Weighted Average Exercise Price, Outstanding, Beginning balance (in dollars per share)	$ 13.39	$ 14.04
Weighted Average Exercise Price, Exercised (in dollars per share)	13.00	14.17
Weighted Average Exercise Price, Expired (in dollars per share)		21.45
Weighted Average Exercise Price, Reserved (in dollars per share)	1.39
Weighted Average Exercise Price, Outstanding, Ending balance (in dollars per share)	$ 2.05	$ 13.39	$ 14.04
Weighted Average Remaining Contractual Life, Outstanding	2 years 4 months 24 days	3 years 8 months 12 days	4 years 6 months
Weighted Average Remaining Contractual Life, Reserved for future issuance	2 years 2 months 12 days
Weighted Average Fair Value, Outstanding, Beginning balance (in dollars per share)	$ 3.38	$ 5.07
Weighted Average Fair Value, Reserved (in dollars per share)	1.22
Weighted Average Fair Value, Outstanding, Ending balance (in dollars per share)	$ 1.34	$ 3.38	$ 5.07