Organization, Basis of Presentation, and Significant Accounting Policies (Details 2) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
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									305	1,483	9,368
Casualty and impairment (gain) loss, net									(3,935)	(10,542)	0
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	242,235	$ 356,392	$ 197,444	$ 237,931	155,428	$ 206,142	$ 172,324	$ 208,144	1,034,002	742,038	683,567
GAAP gain on sale of communities (in excess of) less than tax gain									(204,767)	(20,900)	22,127
Depreciation/amortization timing differences on real estate									(10,183)	(24,657)	(10,735)
Amortization of debt/mark to market interest									(19,763)	(64,676)	(38,202)
Tax compensation expense less than (in excess of) GAAP									5,592	(1,244)	(5,252)
Casualty and impairment (gain) loss, net									(3,935)	(10,542)	0
Other adjustments									(10)	(12,829)	14,323
Taxable net income									$ 800,936	$ 607,190	$ 665,828
Tax components of common stock dividends declared
Ordinary income (as a percent)									68.00%	83.00%	62.00%
20% capital gain (as a percent)									26.00%	12.00%	29.00%
Capital gain tax rate (as a percent)									20.00%	20.00%	20.00%
Unrecaptured 1250 gain (as a percent)									6.00%	5.00%	9.00%
Unsecured notes
Deferred Financing Costs
Accumulated amortization of deferred finance costs	14,008				11,995				$ 14,008	$ 11,995
Secured notes
Deferred Financing Costs
Accumulated amortization of deferred finance costs	10,562				12,315				10,562	12,315
Line of Credit [Member]
Deferred Financing Costs
Accumulated amortization of deferred finance costs	$ 6,490				$ 4,967				6,490	$ 4,967
New England [Member]
Income Tax Disclosure [Abstract]
Casualty and impairment (gain) loss, net									(5,732)
Deferred Financing Costs
Insurance Proceeds									$ 8,493