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