Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2018
Accounting Policies [Abstract]
New accounting pronouncements	ASU 2017-01—The adoption of ASU 2017-01, Business Combinations: Clarifying the Definition of a Business ("ASU 2017-01"), did not have a material impact on the Company's consolidated financial statements. Under ASU 2017-01, certain transactions previously accounted for as business combinations under the former accounting guidance will be accounted for as asset acquisitions under ASU 2017-01. As a result, the Company expects more transaction costs to be capitalized relating to real estate acquisitions as a result of ASU 2017-01. ASU 2017-05—ASU 2017-05, Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets ("ASU 2017-05"), simplifies GAAP by eliminating several accounting differences between transactions involving assets and transactions involving businesses. The amendments in ASU 2017-05 require an entity to initially measure a retained noncontrolling interest in a nonfinancial asset at fair value consistent with how a retained noncontrolling interest in a business is measured. Also, if an entity transfers ownership interests in a consolidated subsidiary that is within the scope of ASC 610-20 and continues to have a controlling financial interest in that subsidiary, ASU 2017-05 requires the entity to account for the transaction as an equity transaction, which is consistent with how changes in ownership interests in a consolidated subsidiary that is a business are recorded when a parent retains a controlling financial interest in the business. The Company adopted ASU 2017-05 using the modified retrospective approach which was applied to all contracts. On January 1, 2018, the Company recorded a step-up in basis to fair value of its retained noncontrolling interest relating to the sale of its ground lease business (refer to Note 4) and other transactions where the Company sold or contributed real estate to a venture and previously recognized partial gains. Prior to the adoption of ASU 2017-05, the Company was required to recognize gains on only the portion of its interest transferred to third parties and was precluded from recognizing a gain on its retained noncontrolling interest which was carried at the Company’s historical cost basis. ASU 2017-12—ASU 2017-12, Derivatives and Hedging - Targeted Improvements to Accounting for Hedging Activities ("ASU 2017-12"), was issued to better align an entity’s risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedge results. ASU 2017-12 expands and refines hedge accounting for both nonfinancial and financial risk components and aligns the recognition and presentation of the effects of the hedging instrument and the hedged item in the financial statements. The Company adopted ASU 2017-12 on January 1, 2018 and the adoption did not have a material impact on the Company's consolidated financial statements. New Accounting Pronouncements—In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses: Measurement of Credit Losses on Financial Instruments ("ASU 2016-13"), which was issued to provide financial statement users with more decision-useful information about the expected credit losses on financial instruments held by a reporting entity. This amendment replaces the incurred loss impairment methodology in current GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. The Company currently records a general reserve that covers performing loans and reserves for loan losses are recorded when: (i) available information as of each balance sheet date indicates that it is probable a loss has occurred in the portfolio; and (ii) the amount of the loss can be reasonably estimated. The formula-based general reserve is derived from estimated principal default probabilities and loss severities applied to groups of loans based upon risk ratings assigned to loans with similar risk characteristics during our quarterly loan portfolio assessment. The Company estimates loss rates based on historical realized losses experienced within its portfolio and take into account current economic conditions affecting the commercial real estate market when establishing appropriate time frames to evaluate loss experience. ASU 2016-13 is effective for interim and annual reporting periods beginning after December 15, 2019. Early adoption is permitted for interim and annual reporting periods beginning after December 15, 2018. Management does not believe the guidance will have a material impact on the Company's consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases ("ASU 2016-02"), and in July 2018, the FASB issued ASU 2018-11, Leases ("ASU 2018-11"), to address two requirements of ASU 2016-02. ASU 2016-02 and ASU 2018-11 are effective for interim and annual reporting periods beginning after December 15, 2018. ASU 2016-02 requires the recognition of lease assets and lease liabilities by lessees for those leases classified as operating or finance leases. For operating and finance leases, a lessee will be required to recognize a right-of-use asset and a lease liability, initially measured at the present value of the lease payments, in its statement of financial position. Lessees under operating leases will be required to recognize a single lease cost, calculated so that the cost of the lease is allocated over the lease term generally on a straight-line basis, and classify all cash payments within operating activities in its statement of cash flows. Lessees under finance leases will be required to recognize interest expense on the lease liability (under the effective interest method) and amortization expense of the right-of-use asset (generally on a straight line basis), each reflected separately in its statement of operations. For operating lease arrangements for which the Company is the lessee, primarily under leases of office space, the Company expects the adoption of ASU 2016-02 to result in the recognition of a right-of-use asset and lease liability on its consolidated balance sheets. The Company does not expect the right-of-use assets or lease liabilities to be material to the Company's balance sheet. The accounting applied by the Company as a lessor will be mostly unchanged from that applied under previous GAAP. Management currently expects to elect the practical expedient package that allows the Company: (a) to not reassess whether any expired or existing contracts entered into prior to January 1, 2019 are or contain leases; (b) to not reassess the lease classification for any expired or existing leases entered into prior to January 1, 2019; and (c) to not reassess initial direct costs for any expired or existing leases entered into prior to January 1, 2019. In addition, the Company will elect to not record on its consolidated balance sheets leases whose term is less than 12 months at lease inception. ASU 2018-11 amends ASU 2016-02 so that: (i) entities may elect to not recast the comparative periods presented when transitioning to ASC 842 by allowing entities to change their initial application to the beginning of the period of adoption; and (ii) provides lessors with a practical expedient to not separate non-lease components from the associated lease component of the contractual payments if certain conditions are met. Management currently expects to elect both of these provisions. The following paragraphs describe the impact on the Company's consolidated financial statements from the adoption of Accounting Standards Updates ("ASUs") on January 1, 2018. ASU 2014-09—ASU 2014-09, Revenue from Contracts with Customers ("ASU 2014-09"), stipulates that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. Certain contracts with customers, including lease contracts and financial instruments and other contractual rights, are not within the scope of the new guidance. The Company's revenue within the scope of the guidance is primarily ancillary income related to its operating properties. The Company adopted ASU 2014-09 using the modified retrospective approach and the adoption did not have a material impact on the Company's consolidated financial statements. ASU 2016-01 and ASU 2018-03—ASU 2016-01, Financial Instruments - Overall: Recognition and Measurement of Financial Assets and Financial Liabilities ("ASU 2016-01"), addressed certain aspects of recognition, measurement, presentation and disclosure of financial instruments. ASU 2018-03, Technical Corrections and Improvements to Financial Instruments - Overall: Recognition and Measurement of Financial Assets and Financial Liabilities, provided technical corrections and improvements to ASU 2016-01. ASU 2016-01 requires entities to measure equity investments not accounted for under the equity method at fair value and recognize changes in fair value in net income. For equity investments without readily determinable fair values, entities may elect a measurement alternative that will allow those investments to be recorded at cost, less impairment, and adjusted for subsequent observable price changes. Upon adoption, entities must record a cumulative-effect adjustment to the balance sheet as of the beginning of the first reporting period in which the standard is adopted. ASU 2016-01 also eliminated the requirement for public business entities to disclose the methods and significant assumptions used to estimate the fair value that is required to be disclosed for financial instruments measured at amortized cost on the balance sheet. The adoption of ASU 2016-01 and ASU 2018-03 did not have a material impact on the Company's consolidated financial statements. ASU 2016-15—ASU 2016-15, Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments ("ASU 2016-15"), was issued to reduce diversity in practice in how certain cash receipts and cash payments, including debt prepayment or debt extinguishment costs, distributions from equity method investees, and other separately identifiable cash flows, are presented and classified in the statement of cash flows. The adoption of ASU 2016-15 was retrospective and resulted in an increase to cash flows provided by operating activities of $11.8 million and a decrease to cash flows provided by financing activities of $11.8 million for the nine months ended September 30, 2017, primarily resulting from the reclassification of cash payments made related to the extinguishment of debt. ASU 2016-18—ASU 2016-18, Statement of Cash Flows: Restricted Cash ("ASU 2016-18"), requires that restricted cash be included with cash and cash equivalents when reconciling beginning and ending cash and cash equivalents on the statement of cash flows and requires disclosure of what is included in restricted cash. The adoption of ASU 2016-18 did not have a material impact on the Company's consolidated financial statements.