Nature of the Business and Operations and Liquidity - Additional Information (Detail) $ in Thousands			1 Months Ended	3 Months Ended		6 Months Ended		66 Months Ended
	May 26, 2017 USD ($)	May 10, 2017 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2017 USD ($) employee	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) employee	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) employee	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)
Description Of Business [Line Items]
Accumulated deficit				$ 978,090		$ 978,090		$ 978,090	$ 955,557
Cash and cash equivalents				30,320	$ 25,262	30,320	$ 25,262	$ 30,320	$ 26,784	$ 39,330
Net cash used in operating activities						13,539	10,912
Restructuring charges				$ (12)	$ 0	$ 1,328	0
Number of workforce persons | employee				321		321		321
Cash flows from financing activities						$ 15,188	$ (2,490)	$ 85,100
Proceeds from additional equity offering	$ 17,000	$ 17,000
INOX Wind Limited
Description Of Business [Line Items]
Strategic agreements value			$ 210,000
Manufacturing agreement period, additional period required			3 years