Basis of Presentation (Policies)	6 Months Ended
Basis of Presentation (Policies)	Jun. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation Our interim consolidated financial statements have been prepared in accordance with the instructions to Form 10-Q and, therefore, do not necessarily include all information and footnotes necessary for a fair statement of our consolidated financial position, results of operations, and cash flows in accordance with generally accepted accounting principles in the United States, or GAAP.
Basis of Consolidation	Basis of Consolidation Our consolidated financial statements reflect all of our accounts, including those of our controlled subsidiaries. The portions of equity in consolidated subsidiaries that are not attributable, directly or indirectly, to us are presented as noncontrolling interests. All significant intercompany accounts and transactions have been eliminated.
Recently Adopted Accounting Policy	When we obtain an economic interest in an entity, we evaluate the entity to determine if it should be deemed a variable interest entity, or VIE, and, if so, whether we are the primary beneficiary and are therefore required to consolidate the entity. We apply accounting guidance for consolidation of VIEs to certain entities in which the equity investors do not have the characteristics of a controlling financial interest or do not have sufficient equity at risk for the entity to finance its activities without additional subordinated financial support from other parties. Fixed price purchase and renewal options within a lease, as well as certain decision-making rights within a loan or joint-venture agreement, can cause us to consider an entity a VIE. Limited partnerships and other similar entities that operate as a partnership will be considered a VIE unless the limited partners hold substantive kick-out rights or participation rights. Significant judgment is required to determine whether a VIE should be consolidated. We review the contractual arrangements provided for in the partnership agreement or other related contracts to determine whether the entity is considered a VIE and to establish whether we have any variable interests in the VIE. We then compare our variable interests, if any, to those of the other variable interest holders to determine which party is the primary beneficiary of the VIE based on whether the entity (i) has the power to direct the activities that most significantly impact the economic performance of the VIE and (ii) has the obligation to absorb losses or the right to receive benefits of the VIE that could potentially be significant to the VIE.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, 2014-09, Revenue from Contracts with Customers (Topic 606). 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 our lease revenues, which constitute a majority of our revenues, but will apply to reimbursed tenant costs and revenues generated from our operating properties. We will adopt this guidance for our annual and interim periods beginning January 1, 2018 using one of two methods: retrospective restatement for each reporting period presented at the time of adoption, or retrospectively with the cumulative effect of initially applying this guidance recognized at the date of initial application. We have not decided which method of adoption we will use. We are evaluating the impact of the new standard and have not yet determined if it will have a material impact on our business or our consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). 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. 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. The new standard also replaces existing sale-leaseback guidance with a new model applicable to both lessees and lessors. Additionally, the new standard requires extensive quantitative and qualitative disclosures. ASU 2016-02 is effective for GAAP public companies for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early application will be permitted for all entities. The new standard must be adopted using a modified retrospective transition of the new guidance and provides for certain practical expedients. Transition will require application of the new model at the beginning of the earliest comparative period presented. The ASU is expected to impact our consolidated financial statements as we have certain operating office and land lease arrangements for which we are the lessee. We are evaluating the impact of the new standard and have not yet determined if it will have a material impact on our business or our consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, Financial Instruments — Credit Losses. ASU 2016-13 introduces a new model for estimating credit losses based on current expected 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 will be effective for public business entities in fiscal years beginning after December 15, 2019, including interim periods within those fiscal years, with early application of the guidance permitted. We are in the process of evaluating the impact of adopting ASU 2016-13 on our consolidated financial statements. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. ASU 2016-15 intends to reduce diversity in practice for certain cash flow classifications, including, but not limited to (i) debt prepayment or debt extinguishment costs, (ii) contingent consideration payments made after a business combination, (iii) proceeds from the settlement of insurance claims, and (iv) distributions received from equity method investees. ASU 2016-15 will be effective for public business entities in fiscal years beginning after December 15, 2017, including interim periods within those fiscal years, with early application of the guidance permitted. We are in the process of evaluating the impact of adopting ASU 2016-15 on our consolidated financial statements and will adopt the standard for the fiscal year beginning January 1, 2018. In October 2016, the FASB issued ASU 2016-17, Consolidation (Topic 810): Interests Held through Related Parties That Are under Common Control. ASU 2016-17 changes how a reporting entity that is a decision maker should consider indirect interests in a VIE held through an entity under common control. If a decision maker must evaluate whether it is the primary beneficiary of a VIE, it will only need to consider its proportionate indirect interest in the VIE held through a common control party. ASU 2016-17 amends ASU 2015-02, which we adopted on January 1, 2016, and which currently directs the decision maker to treat the common control party’s interest in the VIE as if the decision maker held the interest itself. ASU 2016-17 is effective for public business entities in fiscal years beginning after December 15, 2016, including interim periods within those fiscal years. We adopted ASU 2016-17 as of January 1, 2017 on a prospective basis. The adoption of this standard did not have a material impact on our consolidated financial statements. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash. ASU 2016-18 intends to reduce diversity in practice for the classification and presentation of changes in restricted cash on the statement of cash flows. ASU 2016-18 requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 will be effective for public business entities in fiscal years beginning after December 15, 2017, including interim periods within those fiscal years, with early adoption permitted. We are in the process of evaluating the impact of adopting ASU 2016-18 on our consolidated financial statements and will adopt the standard for the fiscal year beginning January 1, 2018. In January 2017, the FASB issued ASU 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business. ASU 2017-01 intends to clarify the definition of a business with the objective of adding guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. Under the current implementation guidance in Topic 805, there are three elements of a business: inputs, processes, and outputs. While an integrated set of assets and activities, collectively referred to as a “set,” that is a business usually has outputs, outputs are not required to be present. ASU 2017-01 provides a screen to determine when a set is not a business. The screen requires that when substantially all of the fair value of the gross assets acquired (or disposed of) is concentrated in a single identifiable asset or a group of similar identifiable assets, the set is not a business. ASU 2017-01 will be effective for public business entities in fiscal years beginning after December 15, 2017, including interim periods within those fiscal years, with early adoption permitted. We elected to early adopt ASU 2017-01 on January 1, 2017 on a prospective basis. While our acquisitions have historically been classified as either business combinations or asset acquisitions, certain acquisitions that were classified as business combinations by us likely would have been considered asset acquisitions under the new standard. As a result, transaction costs are more likely to be capitalized since we expect most of our future acquisitions to be classified as asset acquisitions under this new standard. In addition, goodwill that was previously allocated to businesses that were sold or held for sale will no longer be allocated and written off upon sale if future sales were deemed to be sales of assets and not businesses. In January 2017, the FASB issued ASU 2017-04, Intangibles — Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment. ASU 2017-04 removes step 2 of the goodwill impairment test, which requires a hypothetical purchase price allocation. A goodwill impairment will now be the amount by which a reporting unit’s carrying value exceeds its fair value, not to exceed the carrying amount of goodwill. All other goodwill impairment guidance will remain largely unchanged. Entities will continue to have the option to perform a qualitative assessment to determine if a quantitative impairment test is necessary. ASU 2017-04 will be effective for public business entities in fiscal years beginning after December 15, 2019, including interim periods within those fiscal years in which a goodwill impairment test is performed, with early adoption permitted. We adopted ASU 2017-04 as of April 1, 2017 on a prospective basis. The adoption of this standard did not have a material impact on our 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). ASU 2017-05 clarifies that a financial asset is within the scope of Subtopic 610-20 if it meets the definition of an in substance nonfinancial asset. The amendments define the term “in substance nonfinancial asset,” in part, as a financial asset promised to a counterparty in a contract if substantially all of the fair value of the assets (recognized and unrecognized) that are promised to the counterparty in the contract is concentrated in nonfinancial assets. If substantially all of the fair value of the assets that are promised to the counterparty in a contract is concentrated in nonfinancial assets, then all of the financial assets promised to the counterparty are in substance nonfinancial assets within the scope of Subtopic 610-20. This amendment also clarifies that nonfinancial assets within the scope of Subtopic 610-20 may include nonfinancial assets transferred within a legal entity to a counterparty. For example, a parent company may transfer control of nonfinancial assets by transferring ownership interests in a consolidated subsidiary. ASU 2017-05 is effective for periods beginning after December 15, 2017, with early application permitted for fiscal years beginning after December 15, 2016. We are currently evaluating the impact of ASU 2017-05 on our consolidated financial statements.
Intangible Assets and Liabilities	Amortization of below-market and above-market rent intangibles is recorded as an adjustment to Rental income; amortization of below-market and above-market ground lease intangibles is included in Property expenses; and amortization of in-place lease intangibles is included in Depreciation and amortization expense in the consolidated financial statements
Fair Value Measurements	Derivative Assets — Our derivative assets, which are included in Other assets, net in the consolidated financial statements, are comprised of foreign currency forward contracts, interest rate swaps, interest rate caps, and foreign currency collars (Note 8). These derivative instruments were measured at fair value using readily observable market inputs, such as quotations on interest rates, and were classified as Level 2 as these instruments are custom, over-the-counter contracts with various bank counterparties that are not traded in an active market. Derivative Liabilities — Our derivative liabilities, which are included in Accounts payable, accrued expenses and other liabilities in the consolidated financial statements, are comprised of interest rate swaps and foreign currency collars (Note 8). These derivative instruments were measured at fair value using readily observable market inputs, such as quotations on interest rates, and were classified as Level 2 because they are custom, over-the-counter contracts with various bank counterparties that are not traded in an active market. The fair value of an asset is defined as the exit price, which is the amount that would either be received when an asset is sold or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The guidance establishes a three-tier fair value hierarchy based on the inputs used in measuring fair value. These tiers are: Level 1, for which quoted market prices for identical instruments are available in active markets, such as money market funds, equity securities, and U.S. Treasury securities; Level 2, for which there are inputs other than quoted prices included within Level 1 that are observable for the instrument, such as certain derivative instruments including interest rate caps, interest rate swaps, foreign currency forward contracts and foreign currency collars; and Level 3, for securities that do not fall into Level 1 or Level 2 and for which little or no market data exists, therefore requiring us to develop our own assumptions.
Derivatives	We measure derivative instruments at fair value and record them as assets or liabilities, depending on our 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 income (loss) until the hedged item is recognized in earnings. For a derivative designated, and that qualified, as a net investment hedge, the effective portion of the change in its fair value and/or the net settlement of the derivative is reported in Other comprehensive income (loss) as part of the cumulative foreign currency translation adjustment. The ineffective portion of the change in fair value of any derivative is immediately recognized in earnings.