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Minority Investments - Additional Information (Detail) |  |  | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | ---
Mar. 11, 2016 USD ($) | Oct. 06, 2015 USD ($) | Mar. 31, 2016 USD ($) Item | Sep. 30, 2016 USD ($) | Mar. 31, 2016 USD ($) Item | Mar. 31, 2015 USD ($) | Mar. 31, 2014 USD ($)
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |
Impairment charge on investment |  |  |  |  | $ 746,000 | $ 3,464,000 | $ 1,265,000
Gain on sale of minority interests |  |  |  |  | 3,092,000 |  |
Proceeds from sale of minority interests |  |  |  |  | 3,092,000 |  |
Gain on minority interest investments |  |  |  |  | $ (356,000) | (743,000) | (1,008,000)
Tres Amigas |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |
Number of commonly interconnected power grids | Item |  |  | 3 |  | 3 |  |
Equity method investment, aggregate cost |  |  | $ 5,400,000 |  | $ 5,400,000 |  |
Impairment charge on investment |  |  |  |  | 700,000 |  |
Percentage of minority share investment sold | 100.00% |  |  |  |  |  |
Minority share investment sold, amount | $ 600,000 |  |  |  |  |  |
Gain on sale of minority interests |  |  | 300,000 |  |  |  |
Tres Amigas | Scenario Forecast |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |
Proceeds from sale of minority interests |  |  |  | $ 300,000 |  |  |
Blade Dynamics Ltd |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |
Impairment charge on investment |  |  |  |  |  | $ 3,500,000 | $ 1,300,000
Cost method investment, original cost |  |  | $ 8,000,000 |  | 8,000,000 |  |
Percentage of outstanding common stock |  | 100.00% |  |  |  |  |
Gain on minority interest investments |  |  |  |  | $ 2,800,000 |  |
Milestone achievement period |  | 3 years |  |  |  |  |
Blade Dynamics Ltd | Maximum |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |
Additional proceeds receivable upon successful achievement of certain milestones |  | $ 1,200,000 |  |  |  |  |

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