Business Segments - Operating Results for Two Business Segments (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Segment Reporting Information [Line Items]
Revenues	$ 16,195	$ 27,148	$ 18,507	$ 13,345	$ 27,524	$ 25,772	$ 19,004	$ 23,723	$ 75,195	$ 96,023	$ 70,530
Operating loss	$ (6,988)	$ (4,060)	$ (7,150)	$ (9,344)	$ (1,708)	$ (3,312)	$ (6,841)	$ (8,257)	(27,542)	(20,118)	(52,517)
Unallocated corporate expenses
Segment Reporting Information [Line Items]
Operating loss									(2,892)	(4,027)	(11,306)
Wind
Segment Reporting Information [Line Items]
Revenues									47,269	68,883	51,307
Wind | Operating Segments
Segment Reporting Information [Line Items]
Operating loss									(4,174)	(1,256)	(14,321)
Grid
Segment Reporting Information [Line Items]
Revenues									27,926	27,140	19,223
Grid | Operating Segments
Segment Reporting Information [Line Items]
Operating loss									$ (20,476)	$ (14,835)	$ (26,890)