Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Summary information for the reportable segments
Rental and other property revenues	$ 244,115	$ 240,382	$ 728,467	$ 717,308
Tax credit and asset management revenues	4,789	6,005	17,894	18,127
Total revenues	248,904	246,387	746,361	735,435
Property operating expenses	91,523	88,621	268,225	272,043
Investment management expenses	938	1,905	2,930	4,594
Depreciation and amortization	84,848	77,237	245,356	226,819
General and administrative expenses	11,320	11,013	34,509	33,727
Other expenses, net	1,543	3,590	8,639	7,521
Total operating expenses	190,172	182,366	559,659	544,704
Net operating income (loss)	58,732	64,021	186,702	190,731
Other Items included in income before gain on dispositions (4)	(43,194)	(40,252)	(118,054)	(124,598)
Income before gain on dispositions	15,538	23,769	68,648	66,133
Operating Segments [Member] | Conventional Real Estate Operations [Member]
Summary information for the reportable segments
Rental and other property revenues	203,532	190,702	597,239	559,973
Total revenues	203,532	190,702	597,239	559,973
Property operating expenses	66,888	63,482	194,690	185,408
Total operating expenses	66,888	63,482	194,690	185,408
Net operating income (loss)	136,644	127,220	402,549	374,565
Income before gain on dispositions	136,644	127,220	402,549	374,565
Operating Segments [Member] | Affordable Real Estate Operations [Member]
Summary information for the reportable segments
Rental and other property revenues	25,368	23,610	75,149	70,446
Total revenues	25,368	23,610	75,149	70,446
Property operating expenses	9,869	9,383	29,042	28,166
Total operating expenses	9,869	9,383	29,042	28,166
Net operating income (loss)	15,499	14,227	46,107	42,280
Income before gain on dispositions	15,499	14,227	46,107	42,280
Segment Reconciling Items [Member]
Summary information for the reportable segments
Rental and other property revenues	7,311	7,552	22,046	21,584
Total revenues	7,311	7,552	22,046	21,584
Property operating expenses	2,269	2,279	6,363	6,841
Total operating expenses	2,269	2,279	6,363	6,841
Net operating income (loss)	5,042	5,273	15,683	14,743
Income before gain on dispositions	5,042	5,273	15,683	14,743
Corporate Non-Segment [Member]
Summary information for the reportable segments
Rental and other property revenues	7,904	18,518	34,033	65,305
Tax credit and asset management revenues	4,789	6,005	17,894	18,127
Total revenues	12,693	24,523	51,927	83,432
Property operating expenses	12,497	13,477	38,130	51,628
Investment management expenses	938	1,905	2,930	4,594
Depreciation and amortization	84,848	77,237	245,356	226,819
General and administrative expenses	11,320	11,013	34,509	33,727
Other expenses, net	1,543	3,590	8,639	7,521
Total operating expenses	111,146	107,222	329,564	324,289
Net operating income (loss)	(98,453)	(82,699)	(277,637)	(240,857)
Other Items included in income before gain on dispositions (4)	(43,194)	(40,252)	(118,054)	(124,598)
Income before gain on dispositions	$ (141,647)	$ (122,951)	$ (395,691)	$ (365,455)