Assets Held for Sale and Discontinued Operations - (Details 1) (USD $)	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
Discontinued Operations and Disposal Groups [Line Items]
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest	$ 19,306,000	[1]	$ 18,186,000	[1]	$ 17,943,000	[1]	$ 12,040,000	[1]	$ 26,804,000	[1]	$ 6,977,000	[1]	$ 2,477,000	[1]	$ (1,662,000)	[1]	$ 67,475,000	$ 34,596,000	$ (18,756,000)
Gain on dispositions of real estate, net of tax (Note 12)	26,153,000	[1]	126,329,000	[1]	66,662,000	[1]	69,492,000	[1]									288,636,000	0	0
Provision for real estate impairment losses (3)																	1,820,000	0	6,235,000
Gross proceeds from sale of unconsolidated partnership interests																	640,044,000	357,314,000	484,904,000
Wholly Owned And Consolidated Properties [Member] | Assets Held-for-sale [Member]
Discontinued Operations and Disposal Groups [Line Items]
Number of apartment communities	4																4
Number of apartment homes	371																371
Unconsolidated Properties [Member]
Discontinued Operations and Disposal Groups [Line Items]
Number of apartment communities	11								20								11	20	22
Disposal Group Disposed Of By Sale Not Discontinued Operations [Member] | Wholly Owned And Consolidated Properties [Member]
Discontinued Operations and Disposal Groups [Line Items]
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest																	18,700,000
Gain (Loss) on Sale of Properties, Applicable Income Taxes																	36,100,000
Payments of Debt Extinguishment Costs																	25,200,000
Number of apartment communities	30																30
Number of apartment homes	9,067																9,067
Disposal Group Disposed Of By Sale Not Discontinued Operations [Member] | Unconsolidated Properties [Member]
Discontinued Operations and Disposal Groups [Line Items]
Gross proceeds from sale of unconsolidated partnership interests																	100,000
Number of apartment communities	10																10
Number of apartment homes	439																439
Discontinued Operations, Held-for-sale or Disposed of by Sale [Member] | Wholly Owned And Consolidated Properties [Member]
Discontinued Operations and Disposal Groups [Line Items]
Payments of Debt Extinguishment Costs																		$ 16,500,000	$ 16,500,000
Number of apartment communities									29									29	75
Number of apartment homes									6,953									6,953	11,232

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