Impairment Charges (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Impairment charges on consolidated assets and unconsolidated joint venture investments
Land held for development	$ 40,200,000		$ 40,200,000	$ 54,300,000
Undeveloped land	2,000,000		5,900,000	5,000,000
Assets marketed for sale	9,000,000		22,400,000
Total continuing operations	51,200,000		68,500,000	59,300,000
Impairments Sold Assets or Assets held for sale in discontinued operations	2,400,000	7,100,000	11,300,000	48,400,000
Assets formerly occupied by Mervyns				35,300,000
Total impairment charges included in discontinued operations	2,400,000	7,100,000	11,300,000	83,700,000
Joint venture investments			1,671,000
Total impairment charges	53,600,000	7,100,000	81,400,000	143,000,000
Impairment Charges (Textuals) [Abstract]
Company's share of impairment related to land under development for consolidated joint ventures	36,400,000	0	36,400,000	41,900,000
Company's share of impairment of assets formerly occupied by major tenant	$ 0	$ 0	$ 0	$ 16,500,000