Derivative Instruments and Hedging Activities (Details 1) (Cash Flow Hedging [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Jan. 31, 2012	Jan. 31, 2011	Jan. 31, 2010
Derivative instruments gain loss in financial statements
Gain (Loss) Recognized in OCI (Effective Portion)	$ (48,087)	$ (14,854)	$ 27,386
Gain (loss) reclassified from Accumulated OCI, Effective Amount	(3,886)	(2,921)	(3,444)
Gain (loss) reclassified from Accumulated OCI, Ineffective Amount	(564)	(4)	(2,111)
Interest rate caps, interest rate swaps and Treasury options [Member]
Derivative instruments gain loss in financial statements
Gain (Loss) Recognized in OCI (Effective Portion)	(48,087)	(14,854)	27,386
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	(3,514)	(2,841)	(3,266)
Gain (loss) reclassified from Accumulated OCI, Ineffective Amount	1	1	(1,012)
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	(372)
Gain (loss) reclassified from Accumulated OCI, Ineffective Amount	(565)
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		(80)	(178)
Gain (loss) reclassified from Accumulated OCI, Ineffective Amount		$ (5)	$ (1,099)