Derivative Instruments and Hedging Activities (Details 1) (Cash Flow Hedging [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended
	Apr. 30, 2012	Apr. 30, 2011
Derivative instruments gain loss in financial statements
Gain (Loss) Recognized in OCI (Effective Portion)	$ 8,725	$ (2,039)
Gain (loss) reclassified from Accumulated OCI, Effective Amount	(1,055)	(779)
Gain (loss) reclassified from Accumulated OCI, Ineffective Amount	2
Interest rate caps, interest rate swaps and Treasury options [Member]
Derivative instruments gain loss in financial statements
Gain (Loss) Recognized in OCI (Effective Portion)	8,725	(2,039)
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, Effective Amount	(967)	(691)
Gain (loss) reclassified from Accumulated OCI, Ineffective Amount
Treasury options [Member] | Equity in loss of unconsolidated entities [Member]
Derivative instruments gain loss in financial statements
Gain (loss) reclassified from Accumulated OCI, Effective Amount	(88)	(88)
Gain (loss) reclassified from Accumulated OCI, Ineffective Amount	$ 2