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Minority Investments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended |
--- | --- | ---
Mar. 31, 2014 | Jun. 30, 2014
Tres Amigas |  |
Schedule Of Equity Method Investments [Line Items] |  |
Number of commonly interconnected power grids |  | 3
Equity method investment, aggregate cost |  | $ 5.4
Percentage of ownership interest hold |  | 26.00%
Blade Dynamics Ltd. |  |
Schedule Of Equity Method Investments [Line Items] |  |
Percentage of ownership interest hold |  | 19.00%
Cost method investment, original cost |  | 8.0
Impairment charge on investment | $ 1.3 |

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