Common Stock Warrants Outstanding - Equity-Classified Common Stock Warrants, Outstanding (Detail) - $ / shares	3 Months Ended
	Mar. 31, 2019	Mar. 19, 2019	Feb. 12, 2019	Dec. 31, 2018	Aug. 13, 2018	Jan. 30, 2018
Class Of Warrant Or Right [Line Items]
Weighted Average Exercise Price		$ 1.25	$ 1.20		$ 4.53	$ 1.20
Warrant [Member]
Class Of Warrant Or Right [Line Items]
Total Shares Outstanding	17,799,468			4,694,927
Weighted Average Exercise Price 1.22 [Member] | Warrant [Member]
Class Of Warrant Or Right [Line Items]
Weighted Average Exercise Price	$ 1.22
Total Shares Outstanding	14,204,168
Weighted Average Contractual Life (in years)	5 years 1 month 6 days
Weighted Average Exercise Price 4.21 [Member] | Warrant [Member]
Class Of Warrant Or Right [Line Items]
Weighted Average Exercise Price	$ 4.21
Total Shares Outstanding	3,311,578
Weighted Average Contractual Life (in years)	4 years 4 months 24 days
Weighted Average Exercise Price 25.50 [Member] | Warrant [Member]
Class Of Warrant Or Right [Line Items]
Weighted Average Exercise Price	$ 25.50
Total Shares Outstanding	8,208
Weighted Average Contractual Life (in years)	3 years 8 months 12 days
Weighted Average Exercise Price 33.00 [Member] | Warrant [Member]
Class Of Warrant Or Right [Line Items]
Weighted Average Exercise Price	$ 33.00
Total Shares Outstanding	96,999
Weighted Average Contractual Life (in years)	2 years 7 months 6 days
Weighted Average Exercise Price 45.00 [Member] | Warrant [Member]
Class Of Warrant Or Right [Line Items]
Weighted Average Exercise Price	$ 45.00
Total Shares Outstanding	47,821
Weighted Average Contractual Life (in years)	3 years 4 months 24 days
Weighted Average Exercise Price 75.00 [Member] | Warrant [Member]
Class Of Warrant Or Right [Line Items]
Weighted Average Exercise Price	$ 75.00
Total Shares Outstanding	71,995
Weighted Average Contractual Life (in years)	3 years 6 months
Weighted Average Exercise Price 117.00 [Member] | Warrant [Member]
Class Of Warrant Or Right [Line Items]
Weighted Average Exercise Price	$ 117.00
Total Shares Outstanding	38,772
Weighted Average Contractual Life (in years)	2 years 1 month 6 days
Weighted Average Exercise Price 140.40 [Member] | Warrant [Member]
Class Of Warrant Or Right [Line Items]
Weighted Average Exercise Price	$ 140.40
Total Shares Outstanding	19,339
Weighted Average Contractual Life (in years)	10 months 24 days
Weighted Average Exercise Price 424.80 [Member] | Warrant [Member]
Class Of Warrant Or Right [Line Items]
Weighted Average Exercise Price	$ 424.80
Total Shares Outstanding	588
Weighted Average Contractual Life (in years)	5 years 1 month 6 days