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Nature of the Business and Operations and Liquidity - Additional Information (Detail) $ in Thousands |  | 1 Months Ended | 3 Months Ended | 6 Months Ended | 7 Months Ended | 54 Months Ended |
--- | --- | --- | --- | --- | --- | --- | ---
Apr. 29, 2015 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2016 USD ($) | Mar. 31, 2016 USD ($) | Sep. 30, 2016 USD ($) employee | Sep. 30, 2015 USD ($) | Sep. 30, 2016 USD ($) employee | Sep. 30, 2016 USD ($) employee | Mar. 31, 2015 USD ($)
Description Of Business [Line Items] |  |  |  |  |  |  |  |  |
Accumulated deficit |  |  |  | $ (928,184) | $ (945,864) |  | $ (945,864) | $ (945,864) |
Cash and cash equivalents |  |  |  | 39,330 | 25,262 | $ 32,572 | $ 25,262 | $ 25,262 | $ 20,490
Net cash used in operating activities |  |  |  |  | $ 10,912 | 7,767 |  |  |
Number of workforce persons | employee |  |  |  |  | 366 |  | 366 | 366 |
Cash flows from financing activities |  |  |  |  | $ (2,490) | $ 20,202 |  | $ 68,500 |
Proceeds from additional equity offering | $ 22,300 |  |  |  |  |  |  |  |
Tres Amigas |  |  |  |  |  |  |  |  |
Description Of Business [Line Items] |  |  |  |  |  |  |  |  |
Minority investment, percentage of investment sold |  |  |  |  |  |  | 100.00% |  |
Minority share investment proceeds |  |  |  | $ 300 |  |  | $ 600 |  |
Tres Amigas | Scenario, Forecast |  |  |  |  |  |  |  |  |
Description Of Business [Line Items] |  |  |  |  |  |  |  |  |
Minority share investment proceeds |  |  | $ 300 |  |  |  |  |  |
Maximum | Tres Amigas |  |  |  |  |  |  |  |  |
Description Of Business [Line Items] |  |  |  |  |  |  |  |  |
Minority share investment proceeds |  |  |  |  |  |  | $ 600 |  |
INOX Wind Limited |  |  |  |  |  |  |  |  |
Description Of Business [Line Items] |  |  |  |  |  |  |  |  |
Strategic agreements value |  | $ 210,000 |  |  |  |  |  |  |
Manufacturing agreement period, additional period required |  | 3 years |  |  |  |  |  |  |
INOX Wind Limited | Minimum |  |  |  |  |  |  |  |  |
Description Of Business [Line Items] |  |  |  |  |  |  |  |  |
Period allowable to manufacture the electrical control system |  | 3 years |  |  |  |  |  |  |
INOX Wind Limited | Maximum |  |  |  |  |  |  |  |  |
Description Of Business [Line Items] |  |  |  |  |  |  |  |  |
Period allowable to manufacture the electrical control system |  | 4 years |  |  |  |  |  |  |

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