Business Segments - (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Summary information for the reportable segments
Rental and other property revenues (3)																	$ 952,831		$ 939,231		$ 916,742
Tax credit and asset management revenues																	31,532		34,822		41,769
Total revenues	242,178	[1]	246,843	[1]	246,418	[1]	248,924	[1]	250,862	[1]	243,943	[1]	241,744	[1]	237,504	[1]	984,363		974,053		958,511
Property operating expenses (3)																	373,316		375,672		374,347
Investment management expenses																	7,310		4,341		12,008
Depreciation, Depletion and Amortization																	282,608		291,910		325,173
Provision for real estate impairment losses (3)																	1,820		0		6,235
General and administrative expenses																	44,195		45,708		49,602
Other expenses, net																	12,764		7,403		12,130
Total operating expenses	178,370	[1]	179,376	[1]	180,621	[1]	183,646	[1]	177,707	[1]	179,430	[1]	183,033	[1]	184,864	[1]	722,013		725,034		779,495
Net operating income (loss)	63,808	[1]	67,467	[1]	65,797	[1]	65,278	[1]	73,155	[1]	64,513	[1]	58,711	[1]	52,640	[1]	262,350		249,019		179,016
Other items included in continuing operations																	(194,875)		(214,423)		(197,772)	[2]
Income (loss) from continuing operations	19,306	[1]	18,186	[1]	17,943	[1]	12,040	[1]	26,804	[1]	6,977	[1]	2,477	[1]	(1,662)	[1]	67,475		34,596		(18,756)
Operating Segments [Member] | Conventional Real Estate Operations [Member]
Summary information for the reportable segments
Rental and other property revenues (3)																	767,419	[2]	715,035	[2]	675,929	[2]
Total revenues																	767,419		715,035		675,929
Property operating expenses (3)																	260,451	[2]	247,737	[2]	237,340	[2]
Total operating expenses																	260,451		247,737		237,340
Net operating income (loss)																	506,968		467,298		438,589
Income (loss) from continuing operations																	506,968		467,298		438,589
Operating Segments [Member] | Affordable Real Estate Operations [Member]
Summary information for the reportable segments
Rental and other property revenues (3)																	94,520	[2]	93,053	[2]	91,628	[2]
Total revenues																	94,520		93,053		91,628
Property operating expenses (3)																	38,425	[2]	37,448	[2]	36,565	[2]
Total operating expenses																	38,425		37,448		36,565
Net operating income (loss)																	56,095		55,605		55,063
Income (loss) from continuing operations																	56,095		55,605		55,063
Proportionate Adjustments [Member]
Summary information for the reportable segments
Rental and other property revenues (3)																	32,304	[2],[3]	30,856	[2],[3]	59,561	[2],[3]
Total revenues																	32,304	[3]	30,856	[3]	59,561	[3]
Property operating expenses (3)																	10,283	[3],[4]	10,623	[2],[3]	24,404	[2],[3]
Total operating expenses																	10,283	[3]	10,623	[3]	24,404	[3]
Net operating income (loss)																	22,021	[3]	20,233	[3]	35,157	[3]
Income (loss) from continuing operations																	22,021	[3]	20,233	[3]	35,157	[3]
Corporate Nonsegment And Other Reconciling Items Member [Member]
Summary information for the reportable segments
Rental and other property revenues (3)																	58,588	[2],[4]	100,287	[2],[4]	89,624	[2],[4]
Total revenues																	90,120	[4]	135,109	[4]	131,393	[4]
Property operating expenses (3)																	64,157	[2],[4]	79,864	[2],[4]	76,038	[2],[4]
Total operating expenses																	412,854	[4]	429,226	[4]	481,186	[4]
Net operating income (loss)																	(322,734)	[4]	(294,117)	[4]	(349,793)	[4]
Other items included in continuing operations																	(194,875)	[4]	(214,423)	[4]	(197,772)	[4]
Income (loss) from continuing operations																	$ (517,609)	[4]	$ (508,540)	[4]	$ (547,565)	[4]

[1] Certain reclassifications have been made to quarterly amounts to conform to the full year presentation.

[2] 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), depreciation and amortization and provision for real estate impairment losses. Accordingly, we do not allocate these amounts to our segments.

[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.

[4] Our basis for assessing segment performance excludes the results of apartment communities sold or classified as held for sale. As discussed in Note 12, effective January 1, 2014, we adopted ASU 2014-08, which revised the definition of a discontinued operation. In the segment presentation above, the current year and prior years operating results for apartment communities sold or classified as held for sale during 2014 are presented within the Corporate and Amounts Not Allocated to Segments column. The operating results for the years ended December 31, 2013 and 2012, for apartment communities sold through December 31, 2013, are presented within discontinued operations and are accordingly excluded from the segment presentation above.