Stockholders' Equity - Additional Information (Detail) - USD ($)	1 Months Ended	6 Months Ended
	Dec. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2019
Class Of Stock [Line Items]
Capital stock authorized for issuance		150,000,000
Common stock, shares authorized		145,000,000		145,000,000
Common stock, par value		$ 0.001		$ 0.001
Preferred stock, shares authorized		5,000,000
Preferred stock, par value		$ 0.001
Common stock, shares outstanding		101,748,107		95,506,271
Net proceeds from common stock after deducting advisory fees and offering expenses	$ 250,500,000	$ 250,478,974	$ 60,521,729
Public Offering
Class Of Stock [Line Items]
Shares issued to institutional investors	4,600,000
Aggregate purchase price paid by investors	$ 266,800,000
Net proceeds from common stock after deducting advisory fees and offering expenses	$ 250,500,000
Stock issued, price per share	$ 58.00
2004 Equity Incentive Plan, 2013 Equity Incentive Plan, and Inducement Grants
Class Of Stock [Line Items]
Common Stock, Share reserve for issuance		8,474,561