Fair Value Measurements (Details 2) (Fair value measurement, recurring basis [Member], USD $) In Thousands, unless otherwise specified	Apr. 30, 2012	Jan. 31, 2012
Fair value of financial instruments measured on a recurring basis
Redeemable noncontrolling interest	$ (230,438)	$ (229,149)
Fair value valuation technique credit valuation adjustment of interest rate swap	Potential future exposure
Fair value valuation technique of total return swap	Third party bond pricing
Fair value valuation technique adjustment to borrowings subject to total rate of return swap	Third party bond pricing
Fair value valuation technique of redeemable noncontrolling interest	Discounted cash flows
Fair value unobservable input credit valuation adjustment of interest rate swap	Credit spreads
Fair value unobservable input of total return swap	Bond quote
Fair value unobservable input adjustment to borrowings subject to total rate of return swap	Bond quote
Fair value unobservable input redeemable noncontrolling interest	Discount rate
Percentage of input values redeemable noncontrolling interest	10.30%
Maximum [Member]
Fair value of financial instruments measured on a recurring basis
Percentage of input values credit valuation adjustment of interest rate swap	4.25%
Range of input values of total rate of return swap	102.28%
Range of input values fair values adjustment to borrowings subject to total rate of return swap	100.79%
Minimum [Member]
Fair value of financial instruments measured on a recurring basis
Percentage of input values credit valuation adjustment of interest rate swap	2.72%
Range of input values of total rate of return swap	84.41%
Range of input values fair values adjustment to borrowings subject to total rate of return swap	84.41%
Fair Value, Inputs, Level 3 [Member]
Fair value of financial instruments measured on a recurring basis
Credit valuation adjustment of interest rate swap	14,712
Fair value measurement of total return swap	(10,855)
Fair value adjustment to borrowings subject to total rate of return swap	9,325
Redeemable noncontrolling interest	$ (230,438)	$ (229,149)