Business Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Summary information for the reportable segments
Rental and other property revenues (3)	$ 238,289	[1]	$ 240,136	[1]
Tax credit and asset management revenues	5,976	[2]	8,788	[2]
Total revenues	244,265		248,924
Property operating expenses (3)	95,492	[1]	99,268	[1]
Investment management expenses	1,603	[2]	1,252	[2]
Depreciation and amortization (3)	74,432	[1],[2]	70,307	[1],[2]
General and administrative expenses	10,652	[2]	10,527	[2]
Other expenses, net	1,019	[2]	2,296	[2]
Total operating expenses	183,198		183,650
Net operating income (loss)	61,067		65,274
Other items included in continuing operations	(42,610)		(53,234)
Income from continuing operations	18,457		12,040
Corporate Nonsegment And Other Reconciling Items Member [Member]
Summary information for the reportable segments
Rental and other property revenues (3)	3,472	[1],[2]	25,928	[1],[2]
Total revenues	9,448	[2]	34,716	[2]
Property operating expenses (3)	11,916	[1],[2]	21,650	[1],[2]
Total operating expenses	99,622	[2]	106,032	[2]
Net operating income (loss)	(90,174)	[2]	(71,316)	[2]
Other items included in continuing operations	(42,610)	[2]	(53,234)	[2]
Income from continuing operations	(132,784)	[2]	(124,550)	[2]
Proportionate Adjustments [Member]
Summary information for the reportable segments
Rental and other property revenues (3)	8,732	[1],[3]	7,131	[1],[3]
Total revenues	8,732	[3]	7,131	[3]
Property operating expenses (3)	3,603	[1],[3]	2,451	[1],[3]
Total operating expenses	3,603	[3]	2,451	[3]
Net operating income (loss)	5,129	[3]	4,680	[3]
Income from continuing operations	5,129	[3]	4,680	[3]
Operating Segments [Member] | Conventional Real Estate Operations [Member]
Summary information for the reportable segments
Rental and other property revenues (3)	201,853	[1]	183,696	[1]
Total revenues	201,853		183,696
Property operating expenses (3)	69,743	[1]	64,899	[1]
Total operating expenses	69,743		64,899
Net operating income (loss)	132,110		118,797
Income from continuing operations	132,110		118,797
Operating Segments [Member] | Affordable Real Estate Operations [Member]
Summary information for the reportable segments
Rental and other property revenues (3)	24,232	[1]	23,381	[1]
Total revenues	24,232		23,381
Property operating expenses (3)	10,230	[1]	10,268	[1]
Total operating expenses	10,230		10,268
Net operating income (loss)	14,002		13,113
Income from continuing operations	$ 14,002		$ 13,113

[1] Proportionate property net operating income, our key measurement of segment profit or loss excludes property management revenues (which are included in rental and other property revenues), property management expenses and casualty gains and losses (which are included in property operating expenses) and depreciation and amortization. Accordingly, we do not allocate these amounts to our segments.

[2] Our basis for assessing segment performance excludes the results of apartment communities sold or classified as held for sale. In the segment presentation above, the current year and prior year operating results for apartment communities sold or classified as held for sale during 2015 or 2014 are presented within the Corporate and Amounts Not Allocated to Segments column.

[3] Represents adjustments for the noncontrolling interests in consolidated real estate partnerships’ share of the results of our consolidated apartment communities and the results of consolidated apartment communities that we do not manage, which are excluded from our measurement of segment performance but included in the related consolidated amounts, and our share of the results of operations of our unconsolidated real estate partnerships that we manage, which are included in our measurement of segment performance but excluded from the related consolidated amounts.