Accumulated Other Comprehensive Income (Loss), Net of Tax Unrealized gain on investments Real Estate Investment Property, Accumulated Depreciation Less accumulated depreciation Noncash or Part Noncash Acquisition, Debt Assumed Acquisitions funded by assumed debt Additional Paid in Capital, Common Stock Additional paid-in capital Amortization of Financing Costs and Discounts Amortization of deferred financing fees and debt discounts Gain (Loss) on Sale of Properties Gain on sale of properties Gain on sale of properties Amortization of Intangible Assets Due from Related Parties Due from affiliate Asset Impairment Charges Impairment of assets Impairment of assets Earnings Per Share, Basic Net income, Basic (in dollars per share) Business Acquisition, Pro Forma Information [Text Block] Pro Forma Information (unaudited) Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents Cash and cash equivalents at beginning of year Cash and cash equivalents at end of year Interest Paid Interest paid Increase (Decrease) in Interest Payable, Net Accrued interest Increase (Decrease) in Operating Liabilities Other liabilities Common Stock, Shares Authorized Common shares of beneficial interest, shares authorized Common Stock, Shares, Issued Common shares of beneficial interest, shares issued Common Stock, Shares, Outstanding Common shares of beneficial interest, shares outstanding Common Stock, Value, Issued Common shares of beneficial interest, $0.01 par value: 149,700,000 shares authorized, 141,854,657 and 127,377,665 shares issued and outstanding at December 31, 2010 and 2009, respectively Comprehensive Income Note [Text Block] Comprehensive Income Concentration Risk Disclosure [Text Block] Concentration of Credit Risk Direct Costs of Leased and Rented Property or Equipment Property operating expenses Debt Disclosure [Text Block] Indebtedness Depreciation, Depletion and Amortization, Nonproduction Depreciation Earnings Per Share, Diluted Net income, Diluted (in dollars per share) Equity Method Investments Disclosure [Text Block] Affiliates Insurance Company Income (Loss) from Equity Method Investments Equity in losses of an investee Equity in losses of Affiliates Insurance Company Payments of Financing Costs Payment of deferred financing fees Gains (Losses) on Extinguishment of Debt Loss on early extinguishment of debt Loss on early extinguishment of debt General and Administrative Expense General and administrative Income (Loss) from Continuing Operations, Per Diluted Share Income before gain (loss) on sale of properties, DELETE (in dollars per share) Income (Loss) from Continuing Operations, Per Basic Share Income before gain (loss) on sale oDELETEf properties, Basic (in dollars per share) Income (Loss) from Discontinued Operations, Net of Tax, Per Diluted Share Gain (loss) on sale of properties, DELETE (in dollars per share) Income (Loss) from Discontinued Operations, Net of Tax, Per Basic Share Gain (loss) on sale of DELETE, Basic (in dollars per share) Increase (Decrease) in Other Operating Assets Other assets Finite-Lived Intangible Assets, Net Acquired real estate leases, net Interest Expense Interest expense Investment Building and Building Improvements Land Land Liabilities Total liabilities Liabilities and Stockholders' Equity Total liabilities and shareholders' equity Long-term Line of Credit Unsecured revolving credit facility Available-for-sale Securities Investments in available for sale securities Net Cash Provided by (Used in) Financing Activities Cash provided by financing activities Net Cash Provided by (Used in) Investing Activities Cash used for investing activities Net Cash Provided by (Used in) Operating Activities Cash provided by operating activities Net Cash Provided by (Used in) Operating Activities [Abstract] CASH FLOWS FROM OPERATING ACTIVITIES: Cash and Cash Equivalents, Period Increase (Decrease) Increase (decrease) in cash and cash equivalents Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Text Block] Recent Accounting Pronouncements Operating Leases, Income Statement, Lease Revenue Operating Income (Loss) Operating income Revenues Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Organization Other Assets Other assets Other Liabilities Other liabilities Payments of Dividends, Common Stock Distributions to shareholders Proceeds from Issuance of Common Stock Proceeds from issuance of common shares, net Proceeds from Lines of Credit Proceeds from borrowings on revolving credit facility Proceeds from Issuance of Secured Debt Proceeds from issuance of mortgage debt Proceeds from Issuance of Unsecured Debt Proceeds from issuance of unsecured senior notes, net of discount Payments to Acquire Equity Method Investments Investment in Affiliates Insurance Company Payments to Acquire Real Estate Real estate acquisitions Schedule of Real Estate and Accumulated Depreciation [Text Block] SCHEDULE III REAL ESTATE AND ACCUMULATED DEPRECIATION Real Estate Disclosure [Text Block] Real Estate Properties Real Estate Investment Property, at Cost Total real estate properties, at cost, gross Real Estate Investment Property, Net Total real estate properties, at cost, net Real Estate Revenue, Net Rental income Related Party Transactions Disclosure [Text Block] Related Person Transactions Repayments of Lines of Credit Repayments of borrowings on revolving credit facility Repayments of Subordinated Debt Repayment of junior subordinated debentures Repayments of Other Debt Repayment of other debt Repayments of Unsecured Debt Redemption of senior notes Retained Earnings (Accumulated Deficit) Cumulative net income Schedule of Subsequent Events [Text Block] Subsequent Events Segment Reporting Disclosure [Text Block] Segment Reporting Significant Accounting Policies [Text Block] Summary of Significant Accounting Policies Stockholders' Equity Note Disclosure [Text Block] Shareholders' Equity Notes Assumed Assumption of mortgage notes payable Transfer Other Real Estate Real estate acquisitions Weighted Average Number of Shares Outstanding, Diluted Weighted average shares outstanding, Diluted (in shares) Weighted Average Number of Shares Outstanding, Basic Weighted average shares outstanding (in shares) Common Stock Assets. Total assets Scenario, Unspecified [Domain] Statement [Table] Statement, Scenario [Axis] Statement [Line Items] Statement Capital Lease Obligations Incurred Increase in capital lease obligations Fair Value Disclosures [Text Block] Fair Value of Assets and Liabilities Quarterly Financial Information [Text Block] Selected Quarterly Financial Data (unaudited) Senior Notes Senior unsecured notes due 2012, 2015 and 2020, net of discount Payments to Acquire Available-for-sale Securities, Equity Investment in Five Star Quality Care, Inc. Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity Stockholders' Equity, Period Increase (Decrease) Stockholders' equity, period increase (decrease) Deferred Finance Costs, Net Deferred financing fees, net Increase (Decrease) in Other Operating Liabilities Other liabilities Common Stock, Par or Stated Value Per Share Common shares of beneficial interest, par value (in dollars per share) Income Tax Expense (Benefit) Income tax expense Acquisition Costs Acquisition related costs Off-market Lease, Unfavorable Statement, Equity Components [Axis] Additional Paid-in Capital Cumulative Net Income Unrealized Gain (Loss) on Investments Equity Component [Domain] Increase (Decrease) in Restricted Cash for Operating Activities Restricted cash Stock Issued During Period, Value, New Issues Issuance of shares Stock Issued During Period, Shares, New Issues Issuance of shares (in shares) Replacement Reserve Escrow Restricted cash Stock Issued During Period, Shares, Period Increase (Decrease) Stock issued during period, shares, period increase (decrease) Costs and Expenses Total expenses Dividends, Common Stock Distributions Shares, Issued Beginning balance (in shares) Ending balance (in shares) Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Net income Net income Depreciation, Depletion and Amortization Comprehensive Income, Net of Tax, Including Portion Attributable to Noncontrolling Interest Comprehensive income Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Total shareholders' equity Beginning balance Ending balance Commitments and Contingencies Commitments and contingencies Proceeds from Sale of Real Estate Held-for-investment Proceeds from sale of properties Due to Affiliate Due to affiliate Interest Payable Accrued interest Share grants Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition, Value Issuance of common shares pursuant to our equity compensation plans Stock Granted During Period, Shares, Share-based Compensation Share grants (in shares) Document and Entity Information Significant Tenant Significant Tenant [Text Block] Represents the full disclosure related to significant tenant during the period. Assets [Abstract] ASSETS Real Estate Investment Property, Net [Abstract] Real estate properties, at cost: Liabilities and Stockholders' Equity [Abstract] LIABILITIES AND SHAREHOLDERS' EQUITY Secured debt and capital leases Secured Debt and Capital Lease Obligations Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower and amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date. Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Shareholders' equity: Cumulative distributions Cumulative Common Stock Dividends The amount as of the balance sheet date representing cumulative distributions to common shareholders. Costs and Expenses [Abstract] Expenses: Earnings Per Share, Basic [Abstract] Basic and diluted earnings per share: Diluted earnings per share: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net income to cash provided by operating activities: Increase (Decrease) in Operating Capital [Abstract] Changes in assets and liabilities: Purchases of trading securities Payments for Purchases of Trading Securities The net cash outflow from purchases of trading securities during the period. Trading securities are bought and held principally for the purpose of selling them in the near term (thus held only for a short time). Sales of trading securities Proceeds from Sales of Trading Securities The net cash inflow from sales of trading securities during the period. Trading securities are bought and held principally for the purpose of selling them in the near term (thus held only for a short time). Net Cash Provided by (Used in) Investing Activities [Abstract] CASH FLOWS FROM INVESTING ACTIVITIES: Net Cash Provided by (Used in) Financing Activities [Abstract] CASH FLOWS FROM FINANCING ACTIVITIES: Supplemental Cash Flow Information [Abstract] SUPPLEMENTAL CASH FLOW INFORMATION: NON-CASH INVESTING ACTIVITIES: Non-cash Investing Activities [Abstract] Increase in capital lease assets Increase in Capital Lease Assets The increase during the period in capital lease assets. NON-CASH FINANCING ACTIVITIES: Non-cash Financing Activities [Abstract] Cumulative Distributions Element represents cumulative distributions to common shareholders. SCHEDULE III REAL ESTATE AND ACCUMULATED DEPRECIATION CONSOLIDATED BALANCE SHEETS CONSOLIDATED STATEMENTS OF CASH FLOWS CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY CONSOLIDATED STATEMENTS OF INCOME Interest and Other Income Interest and other income This element represents interest generated from day to day operating activities of the business, earned dividend income on equity securities owned by the entity and includes other income. Acquired real estate lease obligations, net Off Market Lease Unfavorable, Net This element represents a liability associated with the acquisition of an off-market lease when the terms of the lease are unfavorable to the market terms for the lease at the date of acquisition, less accumulated amortization and any impairment charges. Amortization of acquired real estate leases Amortization of Intangible Assets and Liabilities The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) and liabilities in a systematic and rational manner to the periods expected to be impacted from such assets and liabilities. As a noncash expense/ income, this element is added back to/deducted from net income when calculating cash provided by (used in) operations using the indirect method. Buildings, improvements and equipment Investment Building Improvements CIP and Equipment Aggregate of the carrying amounts as of the balance sheet date of investments in buildings, improvements, construction in progress and equipment. Income before gain (loss) on sale of properties and income tax expense This element represents the income or loss from operations before the effects of gain (loss) on sales of properties and income tax expense. Income Loss Before Gain on Sale of Properties and Income Tax Expense Real Estate Properties Indebtedness Shareholders' Equity Fair Value of Assets and Liabilities Segment Reporting Significant Tenant Pro Forma Information (unaudited) Affiliates Insurance Company Summary of Significant Accounting Policies Related Person Transactions Concentration of Credit Risk Selected Quarterly Financial Data (unaudited) Subsequent Events Income before income tax expense This element represents the income or loss from operations before income tax expense. Income Loss Before Income Tax Expense Unrealized Gain on Investments This item represents the disclosure related to the unrealized gains and losses reported in the balance sheet which have resulted from differences between the quoted market prices of the investments and the weighted costs at the date of acquisition. Net Unrealized Gain Loss on Investments Disclosure [Text Block] Recent Accounting Pronouncements Unrealized Gain on Investments Comprehensive Income Organization