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Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions |  | 1 Months Ended | 6 Months Ended |  |
--- | --- | --- | --- | --- | ---
Nov. 18, 2016 | Nov. 30, 2016 | Mar. 31, 2017 | Mar. 21, 2017 | Sep. 30, 2016
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 |  | 5,000,000
Preferred stock, par value |  |  | $ 0.001 |  | $ 0.001
Common stock, shares outstanding |  |  | 74,772,103 |  | 69,746,685
Preferred stock, shares outstanding |  |  | 0 |  | 15,652
Dividend distribution, declared date |  |  | Mar. 21, 2017 |  |
Number of rights distributed for each outstanding share of common stock |  |  |  | 1 |
Dividend distribution, record date |  |  | Mar. 22, 2017 |  |
Rights expiration date |  |  | Mar. 21, 2018 |  |
ARO-LPA Agreement | Amgen |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |
Common stock shares sold | 1,745,810 |  |  |  |
Common stock shares sold, price per share | $ 7.16 |  |  |  |
Net proceeds received |  | $ 12.5 |  |  |
Series C Preferred Stock |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |
Preferred stock, shares converted |  |  | 15,652 |  |
Common stock, issued upon conversion of preferred stock |  |  | 2,670,990 |  |
Preferred stock, shares outstanding |  |  | 0 |  |
Series D Junior Participating Preferred |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |
Preferred stock, par value |  |  |  | $ 0.001 |
Preferred stock conversion of purchase price per one one thousandth of share |  |  |  | $ 0.020 |
Beneficial ownership percentage of common stock upon right exercisable |  |  |  | 15.00% |
Number of rights distributed for each outstanding share of common stock |  |  | 1 |  |
2004 Equity Incentive Plan, 2013 Equity Incentive Plan, and Inducement Grants |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |
Common Stock, Share reserve for issuance |  |  | 8,939,510 |  |

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