Business Segments - Total Business Segments Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018
Segment Reporting Asset Reconciling Item [Line Items]
Total assets	$ 84,446	$ 88,175
Operating Segments | Wind
Segment Reporting Asset Reconciling Item [Line Items]
Total assets	14,830	16,790
Operating Segments | Grid
Segment Reporting Asset Reconciling Item [Line Items]
Total assets	42,701	37,012
Corporate assets
Segment Reporting Asset Reconciling Item [Line Items]
Total assets	$ 26,915	$ 34,373