Income Taxes (Details) (USD $)	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Income Taxes [Abstract]
Minimum dividend required to maintain REIT status	$ 1.01	$ 0.32	$ 0.89
Tax basis of assets	2,700,000,000	2,400,000,000
Tax basis of liabilities	2,000,000,000	1,600,000,000
State income tax expense in rental property and other expenses recorded	100,000	100,000	600,000
Cumulative taxable loss that taxable REIT subsidiary has operated	5,300,000
Deferred tax asset for cumulative tax loss carryforwards	2,000,000
Net deferred tax liabilities	1,600,000
Reserved amount of net deferred tax asset position of taxable REIT subsidiary	$ 400,000

The sum of the tax effects as of the balance sheet date of the amount of excesses of tax deductions over gross income in a year which cannot be used on the tax returns in the current year but can be carried forward to reduce taxable income or income taxes payable in a future year, for which there must be sufficient tax-basis income to utilize a portion or all of the carryforward amount to realize the deferred tax asset.

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The amount as of the balance sheet date of the estimated future tax effects attributable to the difference between the tax basis of capital assets and the basis of capital assets computed in accordance with generally accepted accounting principles. The difference in basis, attributable to different capitalization of costs, depreciation, or amortization methodologies, will increase future taxable income when such basis difference is realized. Capital assets include but are not limited to assets such as land, real estate, leasehold improvements, machinery and equipment and furniture and fixtures.

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- Definition

Amount of an unrecognized tax benefit that is directly related to a position taken in a tax year that results in a net operating loss carryforward. This amount is presented as a reduction of the related deferred tax asset in the balance sheet if that deferred tax asset is not used. This amount is presented separately from the deferred tax asset for a net operating loss carryforward if this unrelated tax benefit is associated with a different tax position.

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- Definition

The amount of the valuation allowance recorded as of the balance sheet date pertaining to the specified deferred tax asset for which an assessment was made that it is more likely than not that all or a portion of such deferred tax asset will not be realized through related deductions on future tax returns.

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