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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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