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Business Segments - Additional Information (Detail) $ in Thousands | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2018 USD ($) segment MW | Dec. 31, 2017 USD ($) | Mar. 31, 2018 segment
Segment Reporting Information [Line Items] |  |  |  |  |
Number of reportable business segments | segment |  |  | 2 |  | 2
Stock-based compensation expense | $ 792 | $ 883 | $ 2,402 | $ 2,115 |
Restructuring charges (less than $0.1 million) | 47 | 1 | 450 | 1,328 |
Change in fair value of contingent consideration | 0 | 272 | 0 | 71 |
Unallocated corporate expenses |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Stock-based compensation expense | 800 | $ 900 | 2,400 | 2,100 |
Restructuring charges (less than $0.1 million) | $ 100 |  | $ 500 | $ 1,300 |
Minimum |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Megawatts of drive trains and power ratings | MW |  |  | 2 |  |

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