Derivative Instruments and Hedging Activities (Details 1) (Cash Flow Hedging [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2012	Jul. 31, 2011
Derivative instruments gain loss in financial statements
Gain (Loss) Recognized in OCI (Effective Portion)	$ (7,019)	$ (20,850)	$ 1,706	$ (22,889)
Gain (loss) reclassified from Accumulated OCI, Effective Amount	(1,073)	(1,038)	(2,128)	(1,817)
Gain (loss) reclassified from Accumulated OCI, Ineffective Amount	6	(555)	8	(555)
Interest rate caps, interest rate swaps and Treasury options [Member]
Derivative instruments gain loss in financial statements
Gain (Loss) Recognized in OCI (Effective Portion)	(7,019)	(20,850)	1,706	(22,889)
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	(980)	(944)	(1,947)	(1,635)
Gain (loss) reclassified from Accumulated OCI, Ineffective Amount	0	0	0	0
Interest rate caps, interest rate swaps and 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	(93)		(181)
Gain (loss) reclassified from Accumulated OCI, Ineffective Amount	6		8
Interest rate caps, swaps and treasury options [Member]
Derivative instruments gain loss in financial statements
Gain (Loss) Recognized in OCI (Effective Portion)	0		0
Interest rate caps and Treasury options [Member]
Derivative instruments gain loss in financial statements
Gain (Loss) Recognized in OCI (Effective Portion)		0		0
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, Effective Amount		(94)		(182)
Gain (loss) reclassified from Accumulated OCI, Ineffective Amount		$ (555)		$ (555)