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Organization and Significant Accounting Policies - Additional Information (Detail) - USD ($) |  | 1 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | ---
Nov. 18, 2016 | Aug. 31, 2016 | Sep. 30, 2016 | Sep. 30, 2015 | Sep. 30, 2014 | Nov. 29, 2016 | Sep. 30, 2013
Schedule Of Investments [Line Items] |  |  |  |  |  |  |
Cash and cash equivalents |  |  | $ 85,366,448 | $ 81,214,354 | $ 132,510,610 |  | $ 19,114,444
Net increase (decrease) in cash |  |  | 4,152,094 | (51,296,256) | 113,396,166 |  |
Proceeds from the issuance of common stock |  | $ 43,200,000 | 52,231,433 |  | 172,641,671 |  |
Proceeds from sale of marketable securities |  |  | 17,308,000 | 26,090,950 | 11,591,120 |  |
Cash outflow related to continuing operating activities |  |  | (64,427,486) | (65,707,615) | $ (35,416,373) |  |
Restricted Cash |  |  | 0 | $ 0 |  |  |
Maximum |  |  |  |  |  |  |
Schedule Of Investments [Line Items] |  |  |  |  |  |  |
Amount insured in FDIC per account |  |  | $ 250,000 |  |  |  |
Property, Plant and Equipment, Useful Life |  |  | 7 years |  |  |  |
Minimum |  |  |  |  |  |  |
Schedule Of Investments [Line Items] |  |  |  |  |  |  |
Property, Plant and Equipment, Useful Life |  |  | 3 years |  |  |  |
Common Stock Purchase Agreement | Amgen |  |  |  |  |  |  |
Schedule Of Investments [Line Items] |  |  |  |  |  |  |
Proceeds from the issuance of common stock |  |  | $ 9,000,000 |  |  |  |
Subsequent Event |  |  |  |  |  |  |
Schedule Of Investments [Line Items] |  |  |  |  |  |  |
Percentage of workforce reduced due to discontinued clinical program |  |  |  |  |  | 30.00% |
Subsequent Event | Amgen | Second Collaboration and License Agreement |  |  |  |  |  |  |
Schedule Of Investments [Line Items] |  |  |  |  |  |  |
Upfront payment | $ 30,000,000 |  |  |  |  |  |
Subsequent Event | Common Stock Purchase Agreement | Amgen |  |  |  |  |  |  |
Schedule Of Investments [Line Items] |  |  |  |  |  |  |
Proceeds from the issuance of common stock | $ 12,500,000 |  |  |  |  |  |
Subsequent Event | Common Stock Purchase Agreement | Amgen | Second Tranche |  |  |  |  |  |  |
Schedule Of Investments [Line Items] |  |  |  |  |  |  |
Common stock issued | 1,745,810 |  |  |  |  |  |

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