Business Segments - Total Business Segments Assets (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 194,193	$ 216,754
Operating Segments [Member] | Wind [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	56,015	67,111
Operating Segments [Member] | Grid [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	72,252	72,800
Unallocated Corporate Expenses [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 65,926	$ 76,843