Significant Accounting Policies (Policy)	12 Months Ended
Significant Accounting Policies (Policy)	Dec. 31, 2013
Policy Text Block [Abstract]
Business Description and Basis of Presentation [Text Block]	The Company - National Health Investors, Inc. ("NHI" or the "Company"), a Maryland corporation incorporated and publicly listed in 1991, is a real estate investment trust (“REIT”) specializing in financing healthcare real estate by purchase and leaseback transactions, RIDEA transactions and mortgage loans. Our investments include senior housing (assisted living, memory care, independent living and senior living campuses), skilled nursing, medical office buildings and specialty hospitals. Revenue is derived primarily from rental income on leased properties, interest income on mortgage loans and income from investments in the securities of other healthcare REITs.
Consolidation, Policy	Principles of Consolidation - The accompanying consolidated financial statements include our accounts and the accounts of our wholly-owned subsidiaries and the joint venture entity over which we exercise control. All inter-company transactions and balances have been eliminated in consolidation. Net income is reduced by the portion of net income attributable to noncontrolling interests. We apply Financial Accounting Standards Board ("FASB") guidance for our arrangements with variable interest entities ("VIEs") which requires us to identify entities for which control is achieved through means other than voting rights and to determine which business enterprise is the primary beneficiary of the VIE. A VIE is broadly defined as an entity with one or more of the following characteristics: (a) the total equity investment at risk is insufficient to finance the entity's activities without additional subordinated financial support; (b) as a group, the holders of the equity investment at risk lack (i) the ability to make decisions about the entity's activities through voting or similar rights, (ii) the obligation to absorb the expected losses of the entity, or (iii) the right to receive the expected residual returns of the entity; or (c) the equity investors have voting rights that are not proportional to their economic interests, and substantially all of the entity's activities either involve, or are conducted on behalf of, an investor that has disproportionately few voting rights. We consolidate investments in VIEs when we are determined to be the primary beneficiary of the VIE. We may change our assessment of a VIE due to events such as modifications of contractual arrangements that affect the characteristics or adequacy of the entity's equity investments at risk and the disposal of all or a portion of an interest held by the primary beneficiary. We identify the primary beneficiary of a VIE as the enterprise that has both: (i) the power to direct the activities of the VIE that most significantly impact the entity's economic performance; and (ii) the obligation to absorb losses or the right to receive benefits of the VIE that could be significant to the entity. We perform this analysis on an ongoing basis. At December 31, 2013, we held an interest in one unconsolidated VIE, of which we were not the primary beneficiary. We also apply FASB guidance related to investments in joint ventures based on the type of controlling rights held by the members' interests in limited liability companies that may preclude consolidation by the majority equity owner in certain circumstances in which the majority equity owner would otherwise consolidate the joint venture. We structure our joint ventures to be compliant with the provisions of the REIT Investment Diversification and Empowerment Act of 2007 ("RIDEA") which permits NHI to receive rent payments through a triple-net lease between a property company and an operating company, and is designed to give NHI the opportunity to capture additional value on the improving performance of the operating company through distributions to a taxable REIT subsidiary ("TRS"). Accordingly, the TRS holds our equity interest in an unconsolidated operating company, which we do not control, and provides an organizational structure that will allow the TRS to engage in a broad range of activities and share in revenues that would otherwise be non-qualifying income under the REIT gross income tests. Equity-Method Investment - We report our TRS' investment in an unconsolidated entity, over whose operating and financial policies we have the ability to exercise significant influence but not control, under the equity method of accounting. Under this method of accounting, our pro rata share of the entity's earnings or losses is included in our Consolidated Statements of Income. Additionally, we adjust our investment carrying amount to reflect our share of changes in an equity-method investee's capital resulting from its capital transactions. The initial carrying value of our equity-method investment is based on the fair value of the net assets of the entity at the time we acquired our interest. We estimate fair values of the net assets of our equity-method investee based on discounted cash flow models. The inputs we use in these models are based on assumptions that we believe to be within a reasonable range of current market rates for the respective investments. We evaluate our equity-method investment for impairment whenever events or changes in circumstances indicate that the carrying value of our investment may exceed the fair value. If it is determined that a decline in the fair value of our investment is not temporary, and if such reduced fair value is below its carrying value, an impairment is recorded. The determination of the fair value of our equity-method investments involve significant judgment. Our estimates consider all available evidence including the present value of the expected future cash flows discounted at market rates, general economic conditions and other relevant factors. Noncontrolling Interest - We present the portion of any equity that we do not own in entities that we control (and thus consolidate) as noncontrolling interest and classify such interest as a component of consolidated equity, separate from total NHI stockholders' equity, in our Consolidated Balance Sheets. In addition, we include net income attributable to the noncontrolling interest in net income in our Consolidated Statements of Income
Use of Estimates, Policy	Use of Estimates - The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the U.S. requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Fair Value Of Financial Instruments	Fair Value Measurements - Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants at the measurement date. A three-level fair value hierarchy is required to prioritize the inputs used to measure fair value. This hierarchy requires entities to maximize the use of observable inputs and minimize the use of unobservable inputs. The three levels of inputs used to measure fair value are as follows: Level 1 - Quoted prices in active markets for identical assets or liabilities. Level 2 - Observable inputs other than quoted prices included in Level 1, such as quoted prices for similar assets and liabilities in active markets; quoted prices for identical or similar assets and liabilities in markets that are not active; or other inputs that are observable or can be corroborated by observable market data. Level 3 - Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. This includes certain pricing models, discounted cash flow methodologies and similar techniques that use significant unobservable inputs. If the fair value measurement is based on inputs from different levels of the hierarchy, the level within which the entire fair value measurement falls is the lowest level input that is significant to the fair value measurement in its entirety. Our assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment and considers factors specific to the asset or liability. When an event or circumstance alters our assessment of the observability and thus the appropriate classification of an input to a fair value measurement which we deem to be significant to the fair value measurement as a whole, we will transfer that fair value measurement to the appropriate level within the fair value hierarchy.
Property, Plant and Equipment, Impairment	Real Estate Properties - Real estate properties are recorded at cost or, if acquired through business combination, at fair value. Cost or fair value at the time of acquisition is allocated among land, buildings, tenant improvements, lease and other intangibles, and personal property. For properties acquired in transactions accounted for as asset purchases, the purchase price allocation is based on the relative fair values of the assets acquired. Cost includes capitalized interest during construction periods. We use the straight-line method of depreciation for buildings over their estimated useful lives of 40 years, and improvements over their estimated useful lives ranging from 3 to 25 years. We evaluate the recoverability of the carrying value of our real estate properties on a property-by-property basis. On a quarterly basis, we review our properties for recoverability when events or circumstances, including significant physical changes in the property, significant adverse changes in general economic conditions and significant deteriorations of the underlying cash flows of the property, indicate that the carrying amount of the property may not be recoverable. The need to recognize an impairment charge is based on estimated undiscounted future cash flows from a property compared to the carrying value of that property. If recognition of an impairment charge is necessary, it is measured as the amount by which the carrying amount of the property exceeds the fair value of the property. We have reclassified for all periods presented the operations of facilities meeting the accounting criteria as either being sold or held for sale as discontinued operations in the Consolidated Statements of Income. Long-lived assets classified as held for sale are reported separately in the Consolidated Balance Sheets. When assets previously classified as being held for sale no longer meet the accounting criteria for such classification, we reclassify those assets as held and used, measured at the lower of their carrying amount before the assets were classified as held for sale (adjusted in the period in which the decision not to sell was made for any depreciation expense that would have been recognized had the assets been continuously classified as held and used) or their fair value at the date of the subsequent decision not to sell. Results of operations of the facilities previously disclosed in our Consolidated Statements of Income as discontinued operations which no longer meet the accounting criteria as held for sale are reclassified into continuing operations for all periods presented. There is no change to reported net income for the prior periods as a result of this reclassification.
Mortgage Notes Receivable	Mortgage and Other Notes Receivable - Each quarter, we evaluate the carrying values of our notes receivable on an instrument-by-instrument basis for recoverability when events or circumstances, including the non-receipt of contractual principal and interest payments, significant deteriorations of the financial condition of the borrower and significant adverse changes in general economic conditions, indicate that the carrying amount of the note receivable may not be recoverable. If a note receivable becomes more than 30 days delinquent as to contractual principal or interest payments, the loan is classified as non-performing, and thereafter we recognize all amounts due when received. If necessary, an impairment is measured as the amount by which the carrying amount exceeds the discounted cash flows expected to be received under the note receivable or, if foreclosure is probable, the fair value of the collateral securing the note receivable.
Cash and Cash Equivalents, Policy [Policy Text Block]	Cash Equivalents - Cash equivalents consist of all highly liquid investments with an original maturity of three months or less.
Concentration Risk, Credit Risk, Policy [Policy Text Block]	Concentration of Credit Risks - Our credit risks primarily relate to cash and cash equivalents, investments in preferred stock and investments in mortgage and other notes receivable. Cash and cash equivalents are primarily held in bank accounts and overnight investments. We maintain our bank deposit accounts with large financial institutions in amounts that often exceed federally-insured limits. We have not experienced any losses in such accounts. Our mortgages and other notes receivable consist primarily of secured loans on health care facilities. Our investment in preferred stock is in another healthcare REIT. Our financial instruments, principally our investments in preferred stock, marketable securities, and notes receivable, are subject to the possibility of loss of the carrying values as a result of either the failure of other parties to perform according to their contractual obligations or changes in market prices which may make the instruments less valuable. We obtain collateral in the form of mortgage liens and other protective rights and continually monitor these rights in order to reduce such possibilities of loss. We evaluate the need to provide for reserves for potential losses on our financial instruments based on management's periodic review of our portfolio on an instrument-by-instrument basis.
Marketable Securities, Policy [Policy Text Block]	Marketable Securities - Our investments in marketable securities are classified as available-for-sale securities. Unrealized gains and losses on available-for-sale securities are recorded in stockholders' equity. We evaluate our marketable securities for other-than-temporary impairments on at least a quarterly basis. Realized gains and losses from the sale of available-for-sale securities are determined on a specific-identification basis. A decline in the market value of any available-for-sale or held-to-maturity security below cost that is deemed to be other-than-temporary results in an impairment to reduce the carrying amount to fair value. The impairment is charged to earnings and a new cost basis for the security is established. To determine whether an impairment is other-than-temporary, we consider whether we have the ability and intent to hold the investment until a market price recovery and consider whether evidence indicating the cost of the investment is recoverable outweighs evidence to the contrary. Evidence considered in this assessment includes the reasons for the impairment, the severity and duration of the impairment, changes in value subsequent to year-end and forecasted performance of the investment.
Deferred Charges, Policy [Policy Text Block]	Deferred Costs - Costs incurred to acquire debt are amortized by the effective interest method over the term of the related debt.
Revenue Recognition, Deferred Revenue [Policy Text Block]	Deferred Income - Deferred income primarily includes non-refundable loan and lease commitment fees received by us, which are amortized into income over the expected period of the related loan or lease. In the event that our financing commitment to a potential borrower or lessee expires, the related commitment fees are recognized into income immediately. Commitment fees may be charged based on the terms of the loan or lease agreements and the creditworthiness of the parties.
Revenue Recognition, Policy [Policy Text Block]	Rental Income - Base rental income is recognized using the straight-line method over the term of the lease. Under certain leases, we receive additional contingent rent, which is calculated on the increase in revenues of the lessee over a base year or base quarter. We recognize contingent rent annually or quarterly when, based on the actual revenues of the lessee, receipt of such income is probable since the target threshold has been achieved. Revenue from minimum lease payments under our leases is recognized on a straight-line basis to the extent that future lease payments are considered collectible. Lease payments that depend on a factor directly related to future use of the property, such as an increase in annual revenues over a base year, are considered to be contingent rentals and are excluded from minimum lease payments. If rental income calculated on a straight-line basis exceeds the cash rent due under a lease, the difference is recorded as an increase to straight-line rent receivable in the Consolidated Balance Sheets and an increase in rental income in the Consolidated Statements of Income. If rental income on a straight-line basis is calculated to be less than cash received, there is a decrease in the same accounts. We identify a lease as non-performing if a required payment is not received within 30 days of the date it is due. Our policy related to rental income on non-performing leased real estate properties is to recognize rental income in the period when the related cash is received. As of December 31, 2013, we had not identified any of our leases as non-performing. Mortgage Interest Income - Mortgage interest income is recognized based on the interest rates and principal amounts outstanding on the mortgage notes receivable. Under certain mortgages, we receive additional contingent interest, which is calculated on the increase in the current year revenues of a borrower over a base year. We identify a mortgage loan as non-performing if a required payment is not received within 30 days of the date it is due. Our policy related to mortgage interest income on non-performing mortgage loans is to recognize mortgage interest income in the period when the cash is received. As of December 31, 2013, we had not identified any of our mortgages as non-performing. Investment Income and Other - Investment income and other includes dividends when declared and interest when earned from investments in preferred stock and marketable securities of other healthcare REITs, interest on cash and cash equivalents when earned, and amortization of deferred income. Realized gains and losses on sales of marketable securities using the specific-identification method are included as a separate component of continuing operations in the Consolidated Statements of Income as investment and other gains.
Derivatives, Policy [Policy Text Block]	Derivatives - In the normal course of business, we are subject to risk from adverse fluctuations in interest rates. We have periodically chosen to manage this risk through the use of derivative financial instruments, primarily interest rate swaps. Counterparties to these contracts are major financial institutions. We are exposed to credit loss in the event of nonperformance by these counterparties. We do not use derivative instruments for trading or speculative purposes. Our objective in managing exposure to market risk is to limit the impact on cash flows. To qualify for hedge accounting, our interest rate swaps must effectively reduce the risk exposure that they are designed to hedge. In addition, at inception of a qualifying cash flow hedging relationship, the underlying transaction or transactions must be, and are expected to remain, probable of occurring in accordance with our related assertions. All of our hedges are cash flow hedges. We recognize all derivative instruments, including embedded derivatives required to be bifurcated, as assets or liabilities at their fair value in the Consolidated Balance Sheets. Changes in the fair value of derivative instruments that are not designated as hedges or that do not meet the criteria of hedge accounting are recognized in earnings. For derivatives designated in qualifying cash flow hedging relationships, the change in fair value of the effective portion of the derivatives is recognized in accumulated other comprehensive income (loss), whereas the change in fair value of the ineffective portion is recognized in earnings.
Income Tax, Policy [Policy Text Block]	Federal Income Taxes - We intend at all times to qualify as a REIT under Sections 856 through 860 of the Internal Revenue Code of 1986, as amended. Effective October 1, 2012, we began recording income tax expense or benefit with respect to one of our subsidiaries which is taxed as a Taxable REIT Subsidiary ("TRS") under provisions similar to those applicable to regular corporations. Aside from such income taxes which may be applicable to the taxable income in the TRS, we will not be subject to U.S. federal income tax, provided that we continue to qualify as a REIT and make distributions to stockholders equal to or in excess of our taxable income. Accordingly, no provision for federal income taxes has been made in the consolidated financial statements, except for the provision on the taxable income of the TRS which is included in franchise, excise and other taxes in the Consolidated Statements of Income. Our failure to continue to qualify under the applicable REIT qualification rules and regulations would have a material adverse impact on our financial position, results of operations and cash flows. Earnings and profits, which determine the taxability of dividends to stockholders, differ from net income reported for financial reporting purposes due primarily to differences in the basis of assets, estimated useful lives used to compute depreciation expense, gains on sales of real estate, non-cash compensation expense and recognition of commitment fees. Our tax returns filed for years beginning in 2010 are subject to examination by taxing authorities. We classify interest and penalties related to uncertain tax positions, if any, in our consolidated financial statements as a component of income tax expense.
Segment Reporting, Policy [Policy Text Block]	Segment Disclosures - We are in the business of owning and financing health care properties. We are managed as one segment, rather than multiple segments for internal purposes and for internal decision making.
New Accounting Pronouncements, Policy	New Accounting Pronouncements - In February 2013, the FASB issued ASU 2013-02, Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income, which amends FASB Topic 220, Comprehensive Income, which requires entities to provide information about amounts reclassified out of accumulated other comprehensive income by component. In addition, an entity is required to present, either on the face of the income statement or in the notes, significant amounts reclassified out of accumulated other comprehensive income by the respective line items of net income. ASU 2013-02 was effective prospectively for reporting periods beginning after December 15, 2012. The adoption of ASU 2013-02 did not have a material impact on our consolidated financial statements. In July 2013 the FASB issued ASU 2013-10, Derivatives and Hedging, which amends Topic 815. ASU 2013-10 permits the Fed Funds Effective Swap Rate (OIS) to be used as a U.S. benchmark interest rate for hedge accounting purposes under Topic 815, in addition to U.S. Treasury and LIBOR. ASU 2013-10 also removes the restriction on using different benchmark rates for similar hedges. ASU 2013-10 is effective prospectively for qualifying new or redesignated hedging relationships entered into on or after July 17, 2013. The adoption of ASU 2013-10 did not have a material impact on our consolidated financial statements