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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