Organization, Basis of Presentation and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Segments	Segments At December 31, 2017, the Company had three reportable operating segments: Core Portfolio, Funds and Structured Financing. The Company’s chief operating decision maker may review operational and financial data on a property basis and does not differentiate properties on a geographical basis for purposes of allocating resources or capital. Each property is considered a separate operating segment; however, each property on a stand-alone basis represents less than 10% of revenues, profit or loss, and assets of the combined reported operating segment and meets the majority of the aggregations criteria under the applicable standard.
Principles of Consolidation	Noncontrolling Interests Noncontrolling interests represent the portion of equity that the Company does not own in those entities it consolidates. The Company identifies its noncontrolling interests separately within the equity section on the Company’s consolidated balance sheets. The amounts of consolidated net earnings attributable to the Company and to the noncontrolling interests are presented separately on the Company’s consolidated statements of income. Noncontrolling interests also include amounts related to common and preferred OP Units issued to unrelated third parties in connection with certain property acquisitions. In addition, the Company periodically issues common OP Units to certain employees of the Company under its share-based incentive program. Unit holders generally have the right to redeem their units for shares of the Company's common stock subject to blackout and other limitations. Common and restricted OP Units are included in the caption Noncontrolling interest within the equity section on the Company’s consolidated balance sheets. Principles of Consolidation The consolidated financial statements include the consolidated accounts of the Company and its investments in partnerships and limited liability companies in which the Company has control in accordance with Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 810 “Consolidation” (“ASC Topic 810”). The ownership interests of other investors in these entities are recorded as noncontrolling interests. All significant intercompany balances and transactions have been eliminated in consolidation. Investments in entities for which the Company has the ability to exercise significant influence over, but does not have financial or operating control, are accounted for using the equity method of accounting. Accordingly, the Company’s share of the earnings (or losses) of these entities are included in consolidated net income.
Cost Method Investments	Cost Method Investments The Company has certain investments to which it applies the cost method of accounting. The Company recognizes as income distributions from net accumulated earnings of the investee since the date of acquisition. The net accumulated earnings of an investee subsequent to the date of investment are recognized by the Company only to the extent distributed by the investee. Distributions received in excess of earnings subsequent to the date of investment are considered a return of investment and are recorded as reductions of cost of the investment. For the periods presented, there have been no events or changes in circumstances that may have a significant adverse effect on the fair value of the Company's cost-method investments.
Use of Estimates	Use of Estimates GAAP requires the Company’s management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. The most significant assumptions and estimates relate to the valuation of real estate, depreciable lives, revenue recognition and the collectability of notes receivable and rents receivable. Application of these estimates and assumptions requires the exercise of judgment as to future uncertainties and, as a result, actual results could differ from these estimates.
Real Estate	Real Estate Land, buildings, and personal property are carried at cost less accumulated depreciation. Improvements and significant renovations that extend the useful life of the properties are capitalized, while replacements, maintenance, and repairs that do not improve or extend the lives of the respective assets are expensed as incurred. Real estate under development includes costs for significant property expansion and development. Depreciation is computed on the straight-line basis over estimated useful lives of the assets as follows: Buildings and improvements Useful lives of 40 years for buildings and 15 years for improvements Furniture and fixtures Useful lives, ranging from five years to 20 years Tenant improvements Shorter of economic life or lease terms Purchase Accounting – Upon acquisitions of real estate, the Company assesses the fair value of acquired assets and assumed liabilities (including land, buildings and improvements, and identified intangibles such as above- and below-market leases and acquired in-place leases and customer relationships) and acquired liabilities in accordance with ASC Topic 805, “Business Combinations” and ASC Topic 350 “Intangibles – Goodwill and Other,” and allocates the acquisition price based on these assessments. The Company assesses fair value of its tangible assets acquired and assumed liabilities based on estimated cash flow projections that utilize appropriate discount and capitalization rates and available market information at the measurement period. Estimates of future cash flows are based on a number of factors including the historical operating results, known trends, and market/economic conditions that may affect the property. In determining the value of above- and below-market leases, the Company estimates the present value difference between contractual rent obligations and estimated market rate of leases at the time of the transaction. To the extent there were fixed-rate options at below-market rental rates, the Company included these along with the current term below-market rent in arriving at the fair value of the acquired leases. The discounted difference between contract and market rents is being amortized to rental income over the remaining applicable lease term, inclusive of any option periods. In determining the value of acquired in-place leases and customer relationships, the Company considers market conditions at the time of the transaction and values the costs to execute similar leases during the expected lease-up period from vacancy to existing occupancy, including carrying costs. The value assigned to in-place leases and tenant relationships is amortized over the estimated remaining term of the leases. If a lease were to be terminated prior to its scheduled expiration, all unamortized costs relating to that lease would be written off. The Company estimates the value of any assumption of mortgage debt based on market conditions at the time of acquisitions including prevailing interest rates, terms and ability to obtain financing for a similar asset. Mortgage debt discounts or premiums are amortized into interest expense over the remaining term of the related debt instrument. Real Estate Under Development – The Company capitalizes certain costs related to the development of real estate. Interest and real estate taxes incurred during the period of the construction, expansion or development of real estate are capitalized and depreciated over the estimated useful life of the building. The Company will cease the capitalization of these costs when construction activities are substantially completed and the property is available for occupancy by tenants, but no later than one year from the completion of major construction activity at which time the project is placed in service and depreciation commences. If the Company suspends substantially all activities related to development of a qualifying asset, the Company will cease capitalization of interest and taxes until activities are resumed. Real Estate Impairment – The Company reviews its real estate and real estate under development for impairment when there is an event or a change in circumstances that indicates that the carrying amount may not be recoverable. In cases where the Company does not expect to recover its carrying costs on properties held for use, the Company reduces its carrying costs to fair value. The determination of anticipated undiscounted cash flows is inherently subjective, requiring significant estimates made by management, and considers the most likely expected course of action at the balance sheet date based on current plans, intended holding periods and available market information. If the Company is evaluating the potential sale of an asset, the undiscounted future cash flows analysis is probability-weighted based upon management’s best estimate of the likelihood of the alternative courses of action as of the balance sheet date. Such cash flow projections consider factors such as expected future operating income, trends and prospects, as well as the effects of demand, competition and other factors. If an impairment is indicated, an impairment loss is recognized based on the excess of the carrying amount of the asset over its fair value. See Note 8 for information about impairment charges incurred during the periods presented.
Dispositions of Real Estate	Dispositions of Real Estate – The Company recognizes property sales in accordance with ASC Topic 970 “Real Estate.” Sales of real estate include the sale of land, operating properties and investments in real estate joint ventures. Gains from dispositions are recognized using the full accrual or partial sale methods, provided that various criteria relating to the terms of sale and any subsequent involvement by the Company with the asset sold are met.
Real Estate Held for Sale	Real Estate Held for Sale – The Company generally considers assets to be held for sale when it has entered into a contract to sell the property, all material due diligence requirements have been satisfied, and management believes it is probable that the disposition will occur within one year. Assets that are classified as held for sale are recorded at the lower of their carrying amount or fair value, less cost to sell.
Notes Receivable	Notes Receivable Notes receivable include certain loans that are held for investment and are collateralized by real estate-related investments and may be subordinate to other senior loans. Notes receivable are recorded at stated principal amounts or at initial investment less accretive yield for loans purchased at a discount, which is accreted over the life of the note. The Company defers loan origination and commitment fees, net of origination costs, and amortizes them over the term of the related loan. The Company evaluates the collectability of both principal and interest based upon an assessment of the underlying collateral value to determine whether it is impaired. A reserve is recorded when, based upon current information and events, it is probable that the Company will be unable to collect all amounts due according to the existing contractual terms. The amount of the reserve is calculated by comparing the recorded investment to the value of the underlying collateral. As the underlying collateral for a majority of the notes receivable is real estate-related investments, the same valuation techniques are used to value the collateral as those used to determine the fair value of real estate investments for impairment purposes. Given the small number of notes outstanding, the Company does not provide for an additional reserve based on the grouping of loans, as the Company believes the characteristics of its notes are not sufficiently similar to allow an evaluation of these notes as a group for a possible loan loss allowance. As such, all of the Company’s notes are evaluated individually for this purpose. Interest income on performing notes is accrued as earned. A note is placed on non-accrual status when, based upon current information and events, it is probable that the Company will not be able to collect all amounts due according to the existing contractual terms. Recognition of interest income on an accrual basis on non-performing notes is resumed when it is probable that the Company will be able to collect amounts due according to the contractual terms.
Investments in and Advances to Unconsolidated Joint Ventures	Investments in and Advances to Unconsolidated Joint Ventures Some of the Company’s joint ventures obtain non-recourse third-party financing on their property investments, contractually limiting the Company’s exposure to losses. The Company recognizes income for distributions in excess of its investment where there is no recourse to the Company and no intention or obligation to contribute additional capital. For investments in which there is recourse to the Company or an obligation or intention to contribute additional capital exists, distributions in excess of the investment are recorded as a liability. When characterizing distributions from equity investees within the Company's consolidated statements of cash flows, all distributions received are first applied as returns on investment to the extent there are cumulative earnings related to the respective investment and are classified as cash inflows from operating activities. If cumulative distributions are in excess of cumulative earnings, distributions are considered return of investment. In such cases, the distribution is classified as cash inflows from investing activities. To the extent that the Company’s carrying basis in an unconsolidated affiliate is different from the basis reflected at the joint venture level, the basis difference is amortized over the life of the related assets and included in the Company’s share of equity in net income (loss) of investments in unconsolidated affiliates the joint venture. The Company periodically reviews its investments in unconsolidated joint ventures for other-than-temporary losses in investment value. Any decline that is not expected to be recovered based on the underlying assets of the investment, is considered other than temporary and an impairment charge is recorded as a reduction in the carrying value of the investment. During the periods presented there were no impairment charges related to the Company’s investments in unconsolidated joint ventures.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less when purchased to be cash equivalents. Cash and cash equivalents are maintained at financial institutions and, at times, balances may exceed the limits insured by the Federal Deposit Insurance Corporation.
Restricted Cash	Restricted Cash Restricted cash consists principally of cash held for real estate taxes, construction costs, property maintenance, insurance, minimum occupancy and property operating income requirements at specific properties as required by certain loan agreements.
Deferred Costs	Deferred Costs Fees and costs paid in the successful negotiation of leases are deferred and amortized on a straight-line basis over the terms of the respective leases. Fees and costs incurred in connection with obtaining financing are deferred and amortized as a component of interest expense over the term of the related debt obligation on a straight-line basis, which approximates the effective interest method. The Company capitalizes salaries, commissions and benefits related to time spent by leasing and legal department personnel involved in originating leases.
Derivative Instruments and Hedging Activities	Derivative Instruments and Hedging Activities The Company measures derivative instruments at fair value and records them as assets or liabilities, depending on its rights or obligations under the applicable derivative contract. Derivatives that are not designated as hedges must be adjusted to fair value through earnings. For a derivative designated and that qualified as a cash flow hedge, the effective portion of the change in fair value of the derivative is recognized in Other comprehensive (loss) income until the hedged item is recognized in earnings. The ineffective portion of a derivative’s change in fair value is immediately recognized in earnings. Although the Company's derivative contracts are subject to master netting arrangements, which serve as credit mitigants to both the Company and its counterparties under certain situations, the Company does not net its derivative fair values or any existing rights or obligations to cash collateral on the consolidated balance sheets. The Company does not use derivatives for trading or speculative purposes. For the periods presented, all of the Company's derivatives qualified and were designated as cash flow hedges, and none of its derivatives were deemed ineffective.
Revenue Recognition and Accounts Receivable	Revenue Recognition and Accounts Receivable Minimum rents from tenants are recognized using the straight-line method over the non-cancelable lease term of the respective leases. Lease termination fees are recognized upon the effective termination of a tenant’s lease when the Company has no further obligations under the lease. As of December 31, 2017 and 2016, unbilled rents receivable relating to the straight-lining of rents of $37.3 million and $34.9 million, respectively, are included in Rents Receivable, net on the accompanying consolidated balance sheets. Certain of these leases also provide for percentage rents based upon the level of sales achieved by the tenant. Percentage rent is recognized in the period when the tenants’ sales breakpoint is met. In addition, leases typically provide for the reimbursement to the Company of real estate taxes, insurance and other property operating expenses. These reimbursements are recognized as revenue in the period the related expenses are incurred. The Company makes estimates of the uncollectability of its accounts receivable related to tenant revenues. An allowance for doubtful accounts has been provided against certain tenant accounts receivable that are estimated to be uncollectible. Once the amount is ultimately deemed to be uncollectible, it is written off. Rents receivable at December 31, 2017 and 2016 are shown net of an allowance for doubtful accounts of $5.9 million and $5.7 million, respectively.
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation expense for all equity-classified stock-based compensation awards is based on the grant date fair value estimated in accordance with current accounting guidance for share-based payments. The Company recognizes these compensation costs for only those shares or units expected to vest on a straight-line or graded-vesting basis, as appropriate, over the requisite service period of the award. The Company includes stock-based compensation within the Additional paid-in capital caption of equity.
Income Taxes	Income Taxes The Company has made an election to be taxed, and believes it qualifies, as a REIT under Sections 856 through 860 of the Internal Revenue Code of 1986, as amended (the “Code”). To maintain REIT status for Federal income tax purposes, the Company is generally required to distribute at least 90% of its REIT taxable income to its shareholders as well as comply with certain other income, asset and organizational requirements as defined in the Code. Accordingly, the Company is generally not subject to Federal corporate income tax to the extent that it distributes 100% of its REIT taxable income each year. In connection with the REIT Modernization Act, the Company is permitted to participate in certain activities and still maintain its qualification as a REIT, so long as these activities are conducted in entities that elect to be treated as taxable subsidiaries under the Code. As such, the Company is subject to Federal and state income taxes on the income from these activities. The Protecting Americans from Tax Hikes Act (PATH Act) was enacted in December 2015, and included numerous law changes applicable to REITs. The provisions have various effective dates beginning as early as 2016. These changes did not materially impact the Company's operations or consolidated financial statements. The Tax Cuts and Jobs Act was enacted in December 2017 and is generally effective for tax years beginning in 2018. This new legislation is not expected to have a material adverse effect on the Company’s business and contains several potentially favorable provisions. However, the Company has recorded an reduction of $2.0 million to its deferred tax assets to reflect the lower Federal corporate tax rate and other provisions effective in 2018. Although it may qualify for REIT status for Federal income tax purposes, the Company is subject to state income or franchise taxes in certain states in which some of its properties are located. In addition, taxable income from non-REIT activities managed through the Company’s taxable REIT subsidiaries (“TRS”) is fully subject to Federal, state and local income taxes. The Company accounts for TRS income taxes under the liability method as required by ASC Topic 740, “Income Taxes.” Under the liability method, deferred income taxes are recognized for the temporary differences between the GAAP basis and tax basis of the TRS income, assets and liabilities. The Company records net deferred tax assets to the extent it believes it is more likely than not that these assets will be realized and would record a valuation allowance to reduce deferred tax assets when it has determined that an uncertainty exists regarding their realization, which would increase the provision for income taxes. In making such determination, the Company considers all available positive and negative evidence, including forecasts of future taxable income, the reversal of other existing temporary differences, available net operating loss carry-forwards, tax planning strategies and recent results of operations. Several of these considerations require assumptions and significant judgment about the forecasts of future taxable income and are consistent with the plans and estimates that the Company is utilizing to manage its business. To the extent facts and circumstances change in the future, adjustments to the valuation allowances may be required.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In May 2014, the FASB issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers. ASU 2014-09 is a comprehensive new revenue recognition model requiring a company to recognize revenue to depict the transfer of goods or services to a customer at an amount reflecting the consideration it expects to receive in exchange for those goods or services. ASU 2014-09 does not apply to the Company’s lease revenues, but will apply to reimbursed tenant costs. Additionally, this guidance modifies disclosures regarding the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. In August 2015, the FASB issued ASU 2015-14, which defers the effective date of ASU 2014-09 for all entities by one year, until years beginning in 2018, with early adoption permitted but not before 2017. Entities may adopt ASU 2014-09 using either a full retrospective approach reflecting the application of the standard in each prior reporting period with the option to elect certain practical expedients or a modified retrospective approach with the cumulative effect recognized at the date of adoption. Substantially all of the Company’s revenue is derived from its leases and therefore falls outside of the scope of this guidance. With respect to its fee-derived revenue, the Company does not anticipate any significant changes to the timing of the Company’s revenue recognition; however, the recognition of gains on sales of properties may be impacted prospectively under limited circumstances under which collectability may not be reasonably assured or if the Company has continuing involvement with a sold property. The Company intends to implement the standard using the modified retrospective approach with the cumulative effect recognized in retained earnings at the date of application. In February 2016, the FASB issued ASU No. 2016-02, Leases. ASU 2016-02 outlines a new model for accounting by lessees, whereby their rights and obligations under substantially all leases, existing and new, would be capitalized and recorded on the balance sheet. As a lessee, the Company is party to various equipment, ground, and office leases with future payment obligations aggregating $207.2 million at December 31, 2017 (Note 11) for which the Company expects to record right-of-use assets upon adoption of ASU 2016-02. For lessors, however, the accounting remains largely unchanged from the current model, with the distinction between operating and financing leases retained, but updated to align with certain changes to the lessee model and the new revenue recognition standard discussed above. The new guidance also requires that internal leasing costs be expensed as incurred, as opposed to capitalized and deferred. The Company expects that it will no longer capitalize a significant portion of internal leasing costs that were previously capitalized. The Company capitalized $1.0 million, $1.1 million and $1.4 million of internal leasing costs during the years ended December 31, 2017, 2016 and 2015, respectively. ASU 2016-02 will also require extensive quantitative and qualitative disclosures and is effective beginning after December 15, 2018, but early adoption is permitted. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses. ASU 2016-13 introduces a new model for estimating credit losses for certain types of financial instruments, including loans receivable, held-to-maturity debt securities, and net investments in direct financing leases, amongst other financial instruments. ASU 2016-13 also modifies the impairment model for available-for-sale debt securities and expands the disclosure requirements regarding an entity’s assumptions, models, and methods for estimating the allowance for losses. ASU 2016-13 is effective for periods beginning after December 15, 2019, with adoption permitted for fiscal years beginning after December 15, 2018. Retrospective adjustments shall be applied through a cumulative-effect adjustment to retained earnings. The adoption of ASU 2016-13 is not expected to have a material impact on the Company’s consolidated financial statements. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows – Classification of Certain Cash Receipts and Cash Payments. ASU 2016-15 provides guidance on certain specific cash flow issues, including, but not limited to, debt prepayment or extinguishment costs, contingent consideration payments made after a business combination and distributions received from equity method investees. ASU 2016-15 is effective for periods beginning after December 15, 2017, with early adoption permitted and shall be applied retrospectively where practicable. The Company expects to elect the “cumulative distribution approach” whereby distributions received from equity method investments would be classified as cash flows from operations to the extent of equity earnings and then as cash flows from investing activities thereafter. Upon the adoption of ASU 2016-15, the Company expects to reclassify $6.3 million and $0 of its cash inflows from investing activities to cash flows from operating activities in its historical presentation of cash flows related to its equity method investments for the years ended December 31, 2017 and 2016, respectively. In January 2017, the FASB issued ASU No. 2017-01, Business Combinations – Clarifying the Definition of a Business. ASU 2017-01 clarifies that to be considered a business, the elements must include, at a minimum, an input and a substantive process that together significantly contribute to the ability to create output. The new standard illustrates the circumstances under which real estate with in-place leases would be considered a business and provides guidance for the identification of assets and liabilities in purchase accounting. ASU 2017-01 is effective for periods beginning after December 15, 2017 and early adoption is permitted. It is expected that the new standard will reduce the number of future real estate acquisitions that will be accounted for as business combinations and, therefore, reduce the amount of acquisition costs that will be expensed. The Company expensed $2.1 million and $8.2 million of acquisition costs during the year ended December 31, 2017 and 2016, respectively. In January 2017, the FASB issued ASU No. 2017-03 Accounting Changes and Error Corrections (Topic 250) and Investments – Equity Method and Joint Ventures (Topic 323). ASU 2017-03 amends certain SEC guidance in the FASB Accounting Standards Codification in response to SEC staff announcements made during 2016 Emerging Issues Task Force (“EITF”) meetings which addressed (i) the additional qualitative disclosures that a registrant is expected to provide when it cannot reasonably estimate the impact that ASUs 2014-09, 2016-02 and 2016-13 will have in applying the guidance in Staff Accounting Bulletin Topic 11.M and (ii) guidance in ASC 323 related to the amendments made by ASU 2014-01 regarding use of the proportional amortization method in accounting for investments in qualified affordable housing projects (announcement made at the November 17, 2016, EITF meeting). The adoption of ASU 2017-03 is not expected to have a material impact on the Company’s consolidated financial statements. In February 2017, the FASB issued ASU 2017-05, Other Income—Gains and Losses from the Derecognition of Nonfinancial Assets (Subtopic 610-20): Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets, which amends the guidance on nonfinancial assets in ASC 610-20. The amendments clarify that (i) a financial asset is within the scope of ASC 610-20 if it meets the definition of an in substance nonfinancial asset and may include nonfinancial assets transferred within a legal entity to a counter-party, (ii) an entity should identify each distinct nonfinancial asset or in substance nonfinancial asset promised to a counter-party and de-recognize each asset when a counter-party obtains control of it, and (iii) an entity should allocate consideration to each distinct asset by applying the guidance in ASC 606 on allocating the transaction price to performance obligations. Further, ASU 2017-05 provides guidance on accounting for partial sales of nonfinancial assets. The amendments are effective at the same time as the amendments in ASU 2014-09. The adoption of ASU 2017-05 is not expected to have a material impact on the Company's consolidated financial statements. In May 2017, the FASB issued ASU 2017-09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting, which clarifies the scope of modification accounting with respect to changes to the terms or conditions of a share-based payment award. Modification accounting would not apply if a change to an award does not affect the total current fair value (or other applicable measurement), vesting conditions, or the classification of the award. For all entities, ASU 2017-09 is effective prospectively for awards modified in fiscal years beginning after December 15, 2017, and interim periods within those annual periods and early adoption is permitted. The adoption of ASU 2017-09 is not expected to have a material impact on the Company's consolidated financial statements because the Company has not historically had significant modifications of its awards. In August 2017, the Financial Accounting Standards Board issued ASU 2017-12, Derivatives and Hedging: Targeted Improvements to Accounting for Hedging Activities. The purpose of this updated guidance is to better align a company’s financial reporting for hedging activities with the economic objectives of those activities. ASU 2017-12 is effective for fiscal years beginning after December 15, 2018, with early adoption, including adoption in an interim period, permitted. The Company plans to adopt ASU 2017-12 effective January 1, 2018. ASU 2017-12 requires a modified retrospective transition method in which the Company will recognize the cumulative effect of the change on the opening balance of each affected component of equity in the statement of financial position as of the date of adoption. The adoption will not have a material impact on the Company’s consolidated financial statements.