Preferred and Common Stock Warrants - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended	9 Months Ended
	Apr. 16, 2019	Mar. 31, 2019	Sep. 30, 2019	Apr. 12, 2019	Mar. 13, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Fair value of warrant purchase					$ 5,200
Gain (loss) on change in fair value of warrant		$ 288
Number of warrants, Issuance of warrants for the purchase of common stock (in shares)			6,035,000
Common stock, par value (in usd per share)			$ 0.001			$ 0.001
Class A Warrant
Class of Stock [Line Items]
Number of warrants, Issuance of warrants for the purchase of common stock (in shares)	3,900,000
Warrant exercise price (usd per share)	$ 13.20			$ 13.20
Pre Funded Warrant
Class of Stock [Line Items]
Number of warrants, Issuance of warrants for the purchase of common stock (in shares)	2,130,000
Warrant exercise price (usd per share)	$ 10.999			$ 10.999
Number of warrants for purchase of convertible preferred shares (in shares)	1
Common stock, par value (in usd per share)	$ 0.001