Stockholders' Equity - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2019
Class Of Stock [Line Items]
Capital stock authorized for issuance	150,000,000	150,000,000
Common stock, shares authorized	145,000,000	145,000,000		145,000,000
Common stock, par value	$ 0.001	$ 0.001		$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, par value	$ 0.001	$ 0.001
Common stock, shares outstanding	101,111,797	101,111,797		95,506,271
Net proceeds from common stock after deducting advisory fees and offering expenses	$ 250,500,000	$ 250,476,739	$ 60,521,729
Public Offering
Class Of Stock [Line Items]
Shares issued to institutional investors	4,600,000	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	$ 58.00
2004 Equity Incentive Plan, 2013 Equity Incentive Plan, and Inducement Grants
Class Of Stock [Line Items]
Common Stock, Share reserve for issuance	6,665,719	6,665,719