Description of Business and Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation Our Consolidated Financial Statements are prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). The Company's Consolidated Financial Statements include the Operating Partnership, wholly owned subsidiaries and those entities in which the Company has the controlling interest. The Operating Partnership's Consolidated Financial Statements include wholly owned subsidiaries and those entities in which the Operating Partnership has the controlling interest. All intercompany transactions and accounts have been eliminated. The unaudited interim consolidated financial statements and accompanying unaudited consolidated financial information, in the opinion of management, contain all adjustments (including normal recurring accruals) necessary for a fair presentation of our financial position, results of operations and cash flows. We have condensed or omitted certain notes and other information from the interim Consolidated Financial Statements presented in this Quarterly Report as permitted by SEC rules and regulations. These Consolidated Financial Statements should be read in conjunction with our 2017 Annual Report on Form 10-K.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in accordance with GAAP requires us to make estimates and assumptions that affect the amounts reported in our Consolidated Financial Statements and accompanying notes. Actual results could differ from those estimates.
Insurance	Insurance Beginning in 2018, we are primarily self-insured for health care claims for eligible participating employees. We have stop-loss coverage to limit our exposure to significant claims on a per claim and annual aggregate basis. We determine our liabilities for claims, including incurred but not reported losses, based on all relevant information, including actuarial estimates of claim liabilities. At June 30, 2018, a reserve of $0.7 million was recorded to cover estimated reported and unreported claims.
Recently Issued Accounting Standards	Recently Issued Accounting Standards The Financial Accounting Standards Board ("FASB") issued an accounting standards update ("ASU") that superseded the revenue recognition requirements under previous guidance, which we adopted as of January 1, 2018. Several updates have been issued subsequently which were intended to promote a more consistent interpretation and application of the principles outlined in the ASU. The ASU requires the use of a new five-step model to recognize revenue from contracts with customers. The five-step model requires that we identify the contract with the customer, identify the performance obligations in the contract, determine the transaction price, allocate the transaction price to the performance obligations in the contract and recognize revenue when we satisfy the performance obligations. We are also required to disclose information regarding the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. In analyzing our contracts with customers, we determined that the most material potential impact from the adoption of this ASU would be in how revenue is recognized for sales of real estate with continuing involvement. Prior to the adoption of this ASU, profit for such sales transactions was recognized and then reduced by the maximum exposure to loss related to the nature of the continuing involvement at the time of sale. Upon adoption of this ASU, any continuing involvement must be analyzed as a separate performance obligation in the contract and a portion of the sales price allocated to each performance obligation. When the continuing involvement performance obligation is satisfied, the sales price allocated to it will be recognized. We had no sales of real estate with continuing involvement during the first six months of 2018 or prior periods; however, we will use such methodology for any future real estate sales with continuing involvement. Our internal controls with respect to accounting for such sales have been updated accordingly. The adoption of this ASU resulted in no other changes with respect to the timing of revenue recognition or internal controls related to our other contracts with customers which include primarily management, development and construction fees and transient parking income, all of which are not material to our Consolidated Financial Statements. As such, there is no cumulative-effect adjustment from the adoption of this ASU reflected in our Consolidated Financial Statements. The FASB issued an ASU that requires entities to show changes in total cash, cash equivalents, restricted cash and restricted cash equivalents in the statement of cash flows. As a result, restricted cash and restricted cash equivalents will be included with cash and cash equivalents when reconciling the beginning of period and end of period balances rather than presented as transfers between cash and cash equivalents and restricted cash and restricted cash equivalents in the statement of cash flows. We adopted the ASU as of January 1, 2018 with retrospective application to our Consolidated Statements of Cash Flows. Accordingly, our Consolidated Statements of Cash Flows present a reconciliation of the changes in cash and cash equivalents and restricted cash. The effect of the adoption resulted in an $8.5 million increase in net cash used in investing activities for the six months ended June 30, 2017. Restricted cash represents cash deposits that are legally restricted or held by third parties on our behalf, such as construction-related escrows, property disposition proceeds set aside and designated or intended to fund future tax-deferred exchanges of qualifying real estate investments, escrows and reserves for debt service, real estate taxes and property insurance established pursuant to certain mortgage financing arrangements and any deposits made with lenders to unencumber secured properties. The FASB issued an ASU that clarifies and narrows the definition of a business used in determining whether to account for a transaction as an asset acquisition or business combination. The guidance requires evaluation of the fair value of the assets acquired to determine if it is concentrated in a single identifiable asset or a group of similar identifiable assets. If so, the transferred assets would not be a business. The guidance also requires a business to include at least one substantive process and narrows the definition of outputs. We adopted the ASU prospectively as of January 1, 2018. We expect that the majority of our future acquisitions would not meet the definition of a business; therefore, the related acquisition costs would be capitalized as part of the purchase price. The FASB issued an ASU that clarifies when changes to the terms or conditions of a share-based payment award must be accounted for as modifications. The guidance requires modification accounting if the value, vesting conditions or classification of the award changes. We adopted the ASU as of January 1, 2018 with no effect on our Consolidated Financial Statements. 1. Description of Business and Significant Accounting Policies – Continued The FASB issued an ASU that sets out the principles for the recognition, measurement, presentation and disclosure of leases for both lessees and lessors. We are continuing to refine our analysis of the impact of the guidance on our Consolidated Financial Statements and the related internal controls and have an active project team working on the evaluation and implementation of the guidance. We continue to monitor FASB activity with respect to possible amendments to this ASU, particularly the FASB’s recent vote to finalize an amendment providing an optional practical expedient to lessors that removes the requirement to separate lease and non-lease components when the pattern of recognition of those components are the same and, when combined as a single unit, those would be classified as operating leases. Should the proposed amendment be issued, we expect to elect the practical expedient as our initial analysis of our leases indicates that the pattern of recognition of our material non-lease components (primarily cost recovery income) are the same as the lease components and will not require the use of the five-step revenue recognition model discussed above. We currently believe that the adoption of the ASU will not significantly change the accounting or the related internal controls for rental and other revenues from operating leases where we are the lessor, and that such leases will be accounted for in a manner similar to existing standards with the underlying leased asset being reported and recognized as a real estate asset. In addition, the guidance requires lessors to capitalize and amortize only incremental direct leasing costs. As a result, upon the adoption of the ASU, we will no longer be able to capitalize and amortize certain leasing related costs and instead will expense these costs as incurred. We are in the process of evaluating the impact to our results of operations of expensing such costs and any necessary changes to our related internal controls. The ASU is required to be adopted in 2019 using a modified retrospective approach which requires a cumulative-effect adjustment to retained earnings as of the beginning of the fiscal year of adoption. Leases where we are the lessee include primarily our operating ground leases. We expect to record right of use assets and the related liabilities for certain of these ground leases. We will continue to refine our evaluation and finalize our implementation plan throughout the remainder of 2018. The FASB issued an ASU that eliminates the requirement to separately measure and report hedge ineffectiveness and generally requires the entire change in the fair value of a hedging instrument to be presented in the same income statement line as the hedged item when the hedged item affects earnings. The ASU is required to be adopted in 2019 using a modified retrospective approach. We do not expect such adoption to have a material effect on our Consolidated Financial Statements. The FASB issued an ASU that requires, among other things, the use of a new current expected credit loss ("CECL") model in determining our allowances for doubtful accounts with respect to accounts receivable, accrued straight-line rents receivable and mortgages and notes receivable. The CECL model requires that we estimate our lifetime expected credit loss with respect to these receivables and record allowances that, when deducted from the balance of the receivables, represent the net amounts expected to be collected. We will also be required to disclose information about how we developed the allowances, including changes in the factors (e.g., portfolio mix, credit trends, unemployment, gross domestic product, etc.) that influenced our estimate of expected credit losses and the reasons for those changes. We will apply the ASU’s provisions as a cumulative-effect adjustment to retained earnings upon adoption in 2020. We are in the process of evaluating this ASU.