Derivative Instruments and Hedging Activities (Details 1) (Cash Flow Hedging [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Oct. 31, 2011	Oct. 31, 2010	Oct. 31, 2011	Oct. 31, 2010
Derivative instruments gain loss in financial statements
Gain (Loss) Recognized in OCI (Effective Portion)	$ (14,867)	$ (13,633)	$ (37,756)	$ (53,747)
Gain (loss) reclassified from Accumulated OCI	(1,034)	(715)	(2,851)	(2,201)
Ineffectiveness Recognized in Interest Expense on Derivatives	(16)	(2)	(571)	(3)
Interest rate caps and treasury options [Member] | Equity in loss of unconsolidated entities [Member]
Derivative instruments gain loss in financial statements
Gain (loss) reclassified from Accumulated OCI	(100)		(282)
Ineffectiveness Recognized in Interest Expense on Derivatives	(17)		(572)
Interest rate caps, interest rate swaps and Treasury options [Member]
Derivative instruments gain loss in financial statements
Gain (Loss) Recognized in OCI (Effective Portion)	(14,867)	(13,633)	(37,756)	(53,747)
Interest rate caps, interest rate swaps and Treasury options [Member] | Interest expense [Member]
Derivative instruments gain loss in financial statements
Gain (loss) reclassified from Accumulated OCI	(934)	(696)	(2,569)	(2,144)
Ineffectiveness Recognized in Interest Expense on Derivatives	1	1	1	2
Treasury options [Member] | Equity in loss of unconsolidated entities [Member]
Derivative instruments gain loss in financial statements
Gain (loss) reclassified from Accumulated OCI		(19)		(57)
Ineffectiveness Recognized in Interest Expense on Derivatives		$ (3)		$ (5)