Description of Business (Detail) - USD ($) $ in Thousands	1 Months Ended	6 Months Ended
	Jul. 31, 2019	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Organization And Description Of Business [Line Items]
Entity incorporation state		Delaware
Entity incorporation date		Aug. 01, 2012
Accumulated Deficit		$ 667,570		$ 527,349
Proceeds from issuance of common stock through underwritten public offering, net		$ 7,630	$ 47,586
Subsequent Event | Underwritten Public Offering
Organization And Description Of Business [Line Items]
Proceeds from issuance of common stock through underwritten public offering, net	$ 140,600