Segment Information (Details) (USD $)	3 Months Ended
	Apr. 30, 2013 segment unit		Apr. 30, 2012	Jan. 31, 2013
Financial data of six reportable segments
Number of strategic business units	3
Number of reportable operating segments	6
Number of reportable operating segments represented by the strategic business units	4
Identifiable assets	$ 10,583,186,000			$ 10,612,432,000
Revenues from real estate operations	305,615,000		287,295,000
Operating expenses	207,804,000		162,986,000
Depreciation and amortization	69,495,000		50,474,000
Interest expense	87,418,000		56,068,000
Interest and other income	11,017,000		10,669,000
Capital expenditures	120,390,000		196,354,000
Commercial Group [Member]
Financial data of six reportable segments
Identifiable assets	6,953,658,000			7,127,228,000
Revenues from real estate operations	181,472,000		173,283,000
Operating expenses	100,804,000		87,609,000
Depreciation and amortization	45,629,000		38,094,000
Interest expense	53,952,000		41,127,000
Interest and other income	2,004,000		3,790,000
Capital expenditures	56,593,000		88,552,000
Commercial Group Land Sales [Member]
Financial data of six reportable segments
Revenues from real estate operations	25,600,000		40,000,000
Operating expenses	15,363,000		3,516,000
Residential Group [Member]
Financial data of six reportable segments
Identifiable assets	2,220,798,000			2,060,892,000
Revenues from real estate operations	63,919,000		61,740,000
Operating expenses	48,578,000		43,165,000
Depreciation and amortization	13,609,000		11,944,000
Interest expense	8,796,000		3,722,000
Interest and other income	6,147,000		4,474,000
Capital expenditures	48,869,000		25,937,000
Arena [Member]
Financial data of six reportable segments
Identifiable assets	998,820,000			980,321,000
Revenues from real estate operations	28,697,000		116,000
Operating expenses	23,951,000		4,288,000
Depreciation and amortization	9,405,000		0
Interest expense	9,013,000		(4,127,000)
Interest and other income	0		0
Capital expenditures	13,886,000		81,587,000
Land Development Group [Member]
Financial data of six reportable segments
Identifiable assets	258,724,000			246,873,000
Revenues from real estate operations	5,927,000		12,156,000
Operating expenses	5,693,000		11,677,000
Depreciation and amortization	98,000		107,000
Interest expense	(102,000)		1,751,000
Interest and other income	2,820,000		2,360,000
Capital expenditures	813,000		42,000
The Nets [Member]
Financial data of six reportable segments
Identifiable assets	(1,870,000)	[1]		1,111,000
Revenues from real estate operations	0		0
Operating expenses	0		0
Depreciation and amortization	0		0
Interest expense	0		0
Interest and other income	0		0
Capital expenditures	0		0
Corporate Activities [Member]
Financial data of six reportable segments
Identifiable assets	153,056,000			196,007,000
Revenues from real estate operations	0		0
Operating expenses	13,415,000		12,731,000
Depreciation and amortization	754,000		329,000
Interest expense	15,759,000		13,595,000
Interest and other income	46,000		45,000
Capital expenditures	$ 229,000		$ 236,000

[1] The identifiable assets of $(1,870) at April 30, 2013 represent losses in excess of the Company's investment basis in The Nets.