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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 |  |

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