Organization, Basis of Presentation, and Significant Accounting Policies (Details 2) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Minimum distribution of adjusted taxable income for deducting dividends from federally taxable income (as a percent)									90.00%
Minimum distribution of REIT taxable income for federal income tax exemption (as a percent)									100.00%
Income Tax Disclosure [Abstract]
Unrecognized tax benefits	$ 0				$ 0				$ 0	$ 0
Excise and sales taxes									0	0	$ 0
Excise tax refund	0				0				0	0	0
Income tax (benefit) expense									(160)	141	305
Casualty and impairment loss (gain), net									215	6,250	(3,935)
Impairment of investment in unconsolidated entities									0	0	0
Reconciliation of Income from Book Basis to Tax Basis Adjustment
Net income attributable to common stockholders	385,734	$ 192,486	$ 254,662	$ 141,643	237,573	$ 238,248	$ 165,225	$ 235,875	974,525	876,921	1,034,002
GAAP gain on sale of communities in excess of tax gain									(194,596)	(86,661)	(195,029)
Depreciation/amortization timing differences on real estate									5,431	(3,642)	(947)
Amortization of debt/mark to market interest									2,276	(18,096)	(18,985)
Tax compensation expense (in excess of) less than GAAP									(612)	3,912	9,821
Casualty and impairment loss (gain), net									19,153	20,243	(657)
Other adjustments									(4,905)	(4,304)	11,533
Taxable net income									$ 801,272	$ 788,373	$ 839,738
Tax components of common stock dividends declared
Ordinary income (as a percent)									76.00%	75.00%	68.00%
20% capital gain (as a percent)									11.00%	18.00%	26.00%
Capital gain tax rate (as a percent)									20.00%	20.00%	20.00%
Unrecaptured 1250 gain (as a percent)									13.00%	7.00%	6.00%
Unsecured notes
Deferred Financing Costs
Accumulated amortization of deferred finance costs	20,564				16,984				$ 20,564	$ 16,984
Secured notes
Deferred Financing Costs
Accumulated amortization of deferred finance costs	2,044				4,991				2,044	4,991
Variable rate unsecured credit facility
Deferred Financing Costs
Accumulated amortization of deferred finance costs	$ 10,108				$ 8,299				10,108	8,299
Land
Income Tax Disclosure [Abstract]
Casualty and impairment loss (gain), net									$ 826	$ 9,350	$ 10,500
New England
Income Tax Disclosure [Abstract]
Casualty and impairment loss (gain), net											(5,732)
Deferred Financing Costs
Insurance recoveries											$ 8,493