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Special Purpose Entities - Additional Information (Detail) (USD $) | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jul. 31, 2014 JointVenture | Jul. 31, 2013 | Jul. 31, 2014 Project JointVenture | Jul. 31, 2013
Variable Interest Entity [Line Items] |  |  |  |
Number of natural gas-fired power plant projects under development |  |  | 2 |
Gains on the deconsolidation of variable interest entities | $ 0 | $ 1,324,000 | $ 0 | $ 2,444,000
Income attributable to the noncontrolling interest | 3,470,000 | 1,300,000 | 4,796,000 | 1,830,000
Number of joint ventures | 2 |  | 2 |
Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |
Gains on the deconsolidation of variable interest entities |  | 1,324,000 |  | 2,444,000
Investment income interest |  | 407,000 |  | 569,000
Income attributable to the noncontrolling interest |  |  |  | $ 261,000

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