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Business Segments - Additional Information (Detail) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) segment MW	Sep. 30, 2017 USD ($)	Mar. 31, 2018 segment
Segment Reporting Information [Line Items]
Number of reportable business segments | segment			2		2
Stock-based compensation expense	$ 825	$ 478	$ 1,610	$ 1,232
Restructuring charges (less than $0.1 million)	93	(12)	403	1,328
Gain on fair value of contingent consideration	0	201	0	201
Unallocated corporate expenses
Segment Reporting Information [Line Items]
Stock-based compensation expense	800	500	1,600	1,200
Restructuring charges (less than $0.1 million)	$ 100	$ 100	$ 400	$ 1,300
Minimum
Segment Reporting Information [Line Items]
Megawatts of drive trains and power ratings | MW			2

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Power of wind turbines.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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