Organization, Basis of Presentation, and Significant Accounting Policies (Details 2) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
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 expense									141	305	1,483
Casualty and impairment loss (gain), net									6,250	(3,935)	(10,542)
Other than Temporary Impairment Losses, Investments									0	0	0
Reconciliation of Income from Book Basis to Tax Basis Adjustment
Net income attributable to common stockholders	237,573	$ 238,248	$ 165,225	$ 235,875	242,235	$ 356,392	$ 197,444	$ 237,931	876,921	1,034,002	742,038
GAAP gain on sale of communities (in excess of) less than tax gain									(85,873)	(195,029)	(20,900)
Depreciation/amortization timing differences on real estate									11,868	(947)	(24,657)
Amortization of debt/mark to market interest									(17,430)	(18,985)	(64,676)
Tax compensation expense less than (in excess of) GAAP									(3,828)	9,821	(1,244)
Casualty and impairment (gain) loss, net									6,250	(657)	(10,542)
Other adjustments									(40,381)	11,533	(12,829)
Taxable net income									$ 747,527	$ 839,738	$ 607,190
Tax components of common stock dividends declared
Ordinary income (as a percent)									75.00%	68.00%	83.00%
20% capital gain (as a percent)									18.00%	26.00%	12.00%
Capital gain tax rate (as a percent)									20.00%	20.00%	20.00%
Unrecaptured 1250 gain (as a percent)									7.00%	6.00%	5.00%
Unsecured notes
Deferred Financing Costs
Accumulated amortization of deferred finance costs	16,984				14,008				$ 16,984	$ 14,008
Secured notes
Deferred Financing Costs
Accumulated amortization of deferred finance costs	4,991				10,562				4,991	10,562
Line of Credit [Member]
Deferred Financing Costs
Accumulated amortization of deferred finance costs	$ 8,299				$ 6,490				8,299	6,490
Land [Member]
Income Tax Disclosure [Abstract]
Casualty and impairment loss (gain), net									$ 9,350		$ 0
New England [Member]
Income Tax Disclosure [Abstract]
Casualty and impairment loss (gain), net										(5,732)
Deferred Financing Costs
Insurance Recoveries										$ 8,493