Business Segments (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Summary information for the reportable segments
Rental and other property revenues		$ 240,382	$ 239,873	$ 717,308	$ 719,501
Tax credit and asset management revenues		6,005	6,970	18,127	22,684
Total revenues		246,387	246,843	735,435	742,185
Property operating expenses		88,621	95,240	272,043	289,008
Investment management expenses		1,905	1,279	4,594	3,552
Depreciation and amortization		77,237	69,437	226,819	211,143
Impairment of Real Estate		0	1,413	0	1,413
General and administrative expenses		11,013	10,658	33,727	31,304
Other expenses, net		3,590	1,349	7,521	7,223
Total operating expenses		182,366	179,376	544,704	543,643
Net operating income (loss)		64,021	67,467	190,731	198,542
Other items included in continuing operations		(40,252)	(49,281)	(124,598)	(150,373)
Income from continuing operations		23,769	18,186	66,133	48,169
Operating Segments [Member] | Conventional Real Estate Operations [Member]
Summary information for the reportable segments
Rental and other property revenues		204,246	187,063	599,977	546,381
Total revenues		204,246	187,063	599,977	546,381
Property operating expenses		68,456	63,869	200,660	187,881
Total operating expenses		68,456	63,869	200,660	187,881
Net operating income (loss)		135,790	123,194	399,317	358,500
Income from continuing operations		135,790	123,194	399,317	358,500
Operating Segments [Member] | Affordable Real Estate Operations [Member]
Summary information for the reportable segments
Rental and other property revenues		24,388	23,724	72,779	70,717
Total revenues		24,388	23,724	72,779	70,717
Property operating expenses		9,631	9,274	28,965	29,129
Impairment of Real Estate					0
Total operating expenses		9,631	9,274	28,965	29,129
Net operating income (loss)		14,757	14,450	43,814	41,588
Income from continuing operations		14,757	14,450	43,814	41,588
Proportionate Adjustments [Member]
Summary information for the reportable segments
Rental and other property revenues	[1]	10,219	7,337	28,269	21,704
Total revenues	[1]	10,219	7,337	28,269	21,704
Property operating expenses	[1]	3,434	2,422	10,274	6,820
Total operating expenses	[1]	3,434	2,422	10,274	6,820
Net operating income (loss)	[1]	6,785	4,915	17,995	14,884
Income from continuing operations	[1]	6,785	4,915	17,995	14,884
Corporate Nonsegment And Other Reconciling Items Member [Member]
Summary information for the reportable segments
Rental and other property revenues	[2]	1,529	21,749	16,283	80,699
Tax credit and asset management revenues	[2]	6,005	6,970	18,127	22,684
Total revenues	[2]	7,534	28,719	34,410	103,383
Property operating expenses	[2]	7,100	19,675	32,144	65,178
Investment management expenses	[2]	1,905	1,279	4,594	3,552
Depreciation and amortization	[2]	77,237	69,437	226,819	211,143
Impairment of Real Estate			1,413		1,413
General and administrative expenses	[2]	11,013	10,658	33,727	31,304
Other expenses, net	[2]	3,590	1,349	7,521	7,223
Total operating expenses	[2]	100,845	103,811	304,805	319,813
Net operating income (loss)	[2]	(93,311)	(75,092)	(270,395)	(216,430)
Other items included in continuing operations	[2]	(40,252)	(49,281)	(124,598)	(150,373)
Income from continuing operations	[2]	$ (133,563)	$ (124,373)	$ (394,993)	$ (366,803)

[1] 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.

[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.