Investments in Unconsolidated Entities (Details 1) (USD $)	3 Months Ended		9 Months Ended
	Oct. 31, 2011	Oct. 31, 2010	Oct. 31, 2011	Oct. 31, 2010	Jan. 31, 2011	Jan. 31, 2010
Real Estate
Completed rental properties	$ 7,126,942,000		$ 7,126,942,000		$ 8,215,425,000
Projects under construction and development	2,237,756,000		2,237,756,000		2,706,235,000
Land held for development or sale	268,685,000		268,685,000		244,879,000
Total Real Estate	9,633,383,000		9,633,383,000		11,166,539,000
Less accumulated depreciation	(1,519,794,000)		(1,519,794,000)		(1,614,399,000)
Real Estate, net	8,113,589,000		8,113,589,000		9,552,140,000
Cash and equivalents	229,656,000	190,240,000	229,656,000	190,240,000	193,372,000	251,405,000
Restricted cash and escrowed funds	457,441,000		457,441,000		720,180,000
Other Assets	610,310,000		610,310,000		759,399,000
Total Assets	8,040,083,000		8,040,083,000		6,320,153,000
Mortgage debt and notes payable, nonrecourse	5,493,372,000		5,493,372,000		7,207,218,000
Members' and partners' equity	997,264,000		997,264,000		587,164,000
Total Liabilities and Members and Partners Equity	8,040,083,000		8,040,083,000		6,320,153,000
Operations:
Revenues	260,808,000	218,500,000	775,828,000	675,177,000
Operating expenses	(169,155,000)	(162,082,000)	(491,834,000)	(486,726,000)
Impairment of real estate	(10,707,000)	(5,703,000)	(15,777,000)	(6,803,000)
Depreciation and amortization - Real Estate Groups	(55,415,000)	(60,367,000)	(166,660,000)	(177,733,000)
Interest and other income	11,294,000	11,919,000	42,116,000	34,964,000
Discontinued operations:
Gain on disposition of rental properties		10,998,000		10,998,000
Discontinued operations subtotal	0	(32,937,000)	125,266,000	(69,823,000)
Net earnings (loss) (pre-tax)	4,814,000	12,344,000	(23,367,000)	(1,259,000)
Company's portion of net earnings (loss) (pre-tax)	1,273,000	22,232,000	11,085,000	19,380,000
Impairment of investment in unconsolidated entities	(41,289,000)	(21,564,000)	(41,289,000)	(36,002,000)
Gain (loss) on disposition of equity method investments			12,567,000	(830,000)
Net earning (loss) (pre-tax) from unconsolidated entities	(40,016,000)	668,000	(17,637,000)	(17,452,000)
Equity Method Investee [Member]
Real Estate
Completed rental properties	7,155,582,000		7,155,582,000		5,514,041,000
Projects under construction and development	351,217,000		351,217,000		174,106,000
Land held for development or sale	226,477,000		226,477,000		272,930,000
Total Real Estate	7,733,276,000		7,733,276,000		5,961,077,000
Less accumulated depreciation	(1,224,318,000)		(1,224,318,000)		(944,968,000)
Real Estate, net	6,508,958,000		6,508,958,000		5,016,109,000
Cash and equivalents	144,173,000		144,173,000		109,246,000
Restricted cash and escrowed funds	325,605,000		325,605,000		384,584,000
Other restricted cash and escrowed funds	307,370,000		307,370,000		206,778,000
Other Assets	753,977,000		753,977,000		536,246,000
Operating property assets held for sale	0		0		67,190,000
Mortgage debt and notes payable, nonrecourse	6,533,871,000		6,533,871,000		5,301,900,000
Other liabilities	508,948,000		508,948,000		369,871,000
Liabilities of operating property held for sale	0		0		61,218,000
Operations:
Operating expenses	(130,799,000)	(112,983,000)	(425,585,000)	(378,785,000)
Interest expense including early extinguishment of debt	(80,043,000)	(67,945,000)	(240,334,000)	(197,938,000)
Impairment of real estate				(1,457,000)
Depreciation and amortization - Real Estate Groups	(48,693,000)	(41,806,000)	(144,344,000)	(122,383,000)
Interest and other income	3,541,000	4,190,000	11,068,000	11,515,000
Earnings (loss) form continuing operations	4,814,000	(44,000)	(23,367,000)	(13,871,000)
Discontinued operations:
Operating earnings from rental properties		1,390,000		1,614,000
Gain on disposition of rental properties		10,998,000		10,998,000
Discontinued operations subtotal		12,388,000		12,612,000
Impairment of investment in unconsolidated entities	$ (41,289,000)	$ (21,564,000)	$ (41,289,000)	$ (36,002,000)