Business Segments - Operating Results for Two Business Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Revenues	$ 11,049	$ 18,507	$ 19,971	$ 31,852
Operating loss	(7,805)	(7,150)	(22,499)	(16,494)
Unallocated corporate expenses
Segment Reporting Information [Line Items]
Operating loss	(265)	(653)	(2,358)	(1,653)
Wind
Segment Reporting Information [Line Items]
Revenues	5,554	12,898	7,831	18,573
Wind | Operating Segments
Segment Reporting Information [Line Items]
Operating loss	(1,440)	(1,235)	(5,873)	(4,264)
Grid
Segment Reporting Information [Line Items]
Revenues	5,495	5,609	12,140	13,279
Grid | Operating Segments
Segment Reporting Information [Line Items]
Operating loss	$ (6,100)	$ (5,262)	$ (14,268)	$ (10,577)