Common Stock - Summary of Common Stock Reserved and Unreserved for Future Issuance (Detail) - shares		12 Months Ended
		Dec. 31, 2018	Sep. 13, 2018	Sep. 12, 2018	Dec. 31, 2017
Class Of Stock Disclosures [Abstract]
Common stock, shares authorized		200,000,000	200,000,000	100,000,000	100,000,000
Common stock issued and outstanding		9,078,238
Common stock reserved for the exercises of common stock warrants	[1]	7,345,103
Common stock reserved for the exercise of options		353,274
Common stock reserved for other		497
Common stock reserved for future awards under the Plans (Note 13)		1,499,934
Total common stock issued and reserved for future issuance		18,277,046
Unreserved common stock available for future issuance		181,722,954

[1] The 1,612 warrants for the redeemable preferred stock require 150% common stock reserve