Elme Communities (ELME) 10-K 20 Feb 18 2017 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 15, 2018	Jun. 30, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	WASHINGTON REAL ESTATE INVESTMENT TRUST
Entity Central Index Key	104,894
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		78,497,963
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 2,436,739,462

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets
Land	$ 588,025	$ 573,315
Income producing property	2,113,977	2,112,088
Real estate investment property, at cost	2,702,002	2,685,403
Accumulated depreciation and amortization	(683,692)	(657,425)
Net income producing property	2,018,310	2,027,978
Properties under development or held for future development	54,422	40,232
Total real estate held for investment, net	2,072,732	2,068,210
Investment in real estate sold or held for sale, net	68,534	0
Cash and cash equivalents	9,847	11,305
Restricted cash	2,776	6,317
Rents and other receivables, net of allowance for doubtful accounts of $2,426 and $2,377, respectively	69,766	64,319
Prepaid expenses and other assets	125,087	103,468
Other assets related to properties sold or held for sale	10,684	0
Total assets	2,359,426	2,253,619
Liabilities
Notes payable, net	894,358	843,084
Mortgage notes payable, net	95,141	148,540
Lines of credit	166,000	120,000
Accounts payable and other liabilities	61,565	46,967
Dividends payable	23,581	22,414
Advance rents	12,487	11,750
Tenant security deposits	9,149	8,802
Other liabilities related to properties sold or held for sale	1,809	0
Total liabilities	1,264,090	1,201,557
Shareholders’ equity
Preferred shares; $0.01 par value; 10,000 shares authorized; no shares issued or outstanding	0	0
Shares of beneficial interest; $0.01 par value; 100,000 shares authorized: 78,510 and 74,606 shares issued and outstanding at December 31, 2017 and 2016, respectively	785	746
Additional paid in capital	1,483,980	1,368,636
Distributions in excess of net income	(399,213)	(326,047)
Accumulated other comprehensive income	9,419	7,611
Total shareholders’ equity	1,094,971	1,050,946
Noncontrolling interests in subsidiary	365	1,116
Total equity	1,095,336	1,052,062
Total liabilities and equity	$ 2,359,426	$ 2,253,619

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Rents and receivables, allowance for doubtful accounts	$ 2,426	$ 2,377
Preferred shares, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred shares, authorized (in shares)	10,000	10,000
Preferred shares, issued (in shares)	0	0
Preferred shares, outstanding (in shares)	0	0
Shares of beneficial interest, par value (in dollars per share)	$ 0.01	$ 0.01
Shares of beneficial interest, authorized (in shares)	100,000	100,000
Shares of beneficial interest, issued (in shares)	78,510	74,606
Shares of beneficial interest, outstanding (in shares)	78,510	74,606

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue
Real estate rental revenue	$ 325,078	$ 313,264	$ 306,427
Expenses
Real estate expenses	115,650	115,013	112,234
Depreciation and amortization	112,056	108,406	108,935
Acquisition costs	0	1,178	2,056
Real estate impairment and casualty (gain), net	33,152	(676)	5,909
General and administrative	22,580	19,545	20,123
Total expenses	283,438	243,466	249,257
Other operating income
Gain on sale of real estate	24,915	101,704	91,107
Real estate operating income	66,555	171,502	148,277
Other income (expense)
Interest expense	(47,534)	(53,126)	(59,546)
Other income	507	297	709
Loss on extinguishment of debt	0	0	(119)
Income tax benefit (expense)	84	615	(134)
Total other income (expense)	(46,943)	(52,214)	(59,090)
Net income	19,612	119,288	89,187
Less: Net loss attributable to noncontrolling interests in subsidiaries	(56)	(51)	(553)
Net income attributable to the controlling interests	$ 19,668	$ 119,339	$ 89,740
Basic net income attributable to the controlling interests per share
Basic net income attributable to the controlling interests per share (in dollars per share)	$ 0.25	$ 1.65	$ 1.31
Diluted net income attributable to the controlling interests per share
Diluted net income attributable to the controlling interests per share (in dollars per share)	$ 0.25	$ 1.65	$ 1.31
Weighted average shares outstanding – basic (in shares)	76,820	72,163	68,177
Weighted average shares outstanding – diluted (in shares)	76,935	72,339	68,310

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 19,612	$ 119,288	$ 89,187
Unrealized gain (loss) on interest rate hedges	1,808	8,161	(550)
Comprehensive income	21,420	127,449	88,637
Less: Net loss attributable to noncontrolling interests in subsidiaries	(56)	(51)	(553)
Comprehensive income attributable to the controlling interests	$ 21,476	$ 127,500	$ 89,190

Consolidated Statements of Equi

Consolidated Statements of Equity - USD ($) shares in Thousands, $ in Thousands	Total	Shares Of Beneficial Interest At Par Value [Member]	Additional Paid In Capital [Member]	Distributions In Excess Of Net Income Attributable To The Controlling Interests [Member]	AOCI Attributable to Parent [Member]	Total Shareholders' Equity [Member]	Noncontrolling Interests In Subsidiaries [Member]
Balance, shares at Dec. 31, 2014		67,819
Balance at Dec. 31, 2014	$ 822,229	$ 678	$ 1,184,395	$ (365,518)	$ 0	$ 819,555	$ 2,674
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to the controlling interests	89,740			89,740		89,740
Net loss attributable to noncontrolling interests and deconsolidation of noncontrolling interest	553
Net loss attributable to noncontrolling interests	(1,316)						(1,316)
Unrealized gain (loss) on interest rate hedges	(550)				(550)	(550)
Contributions from noncontrolling interest	5						5
Dividends	(82,003)			(82,003)		(82,003)
Stock issued during period (in shares)		184
Equity offerings, net of issuance costs	5,215	$ 2	5,213			5,215
Share grants, net of share grant amortization and forfeitures (in shares)		188
Share grants, net of share grant amortization and forfeitures	3,692	$ 2	3,690			3,692
Balance, shares at Dec. 31, 2015		68,191
Balance at Dec. 31, 2015	837,012	$ 682	1,193,298	(357,781)	(550)	835,649	1,363
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to the controlling interests	119,339			119,339		119,339
Net loss attributable to noncontrolling interests and deconsolidation of noncontrolling interest	51						51
Unrealized gain (loss) on interest rate hedges	8,161				8,161	8,161
Distributions to noncontrolling interests	(196)						(196)
Dividends	(87,570)			(87,570)		(87,570)
Stock issued during period (in shares)		6,223
Equity offerings, net of issuance costs	172,936	$ 62	172,874			172,936
Shares issued under Dividend Reinvestment Program (in shares)		23
Shares issued under Dividend Reinvestment Program	700		700			700
Share grants, net of share grant amortization and forfeitures (in shares)		169
Share grants, net of share grant amortization and forfeitures	1,766	$ 2	1,764			1,766
Balance, shares at Dec. 31, 2016		74,606
Balance at Dec. 31, 2016	1,052,062	$ 746	1,368,636	(326,047)	7,611	1,050,946	1,116
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustment for retrospective application of new accounting principle (see note 2)	(35)			(35)		(35)
Net income attributable to the controlling interests	19,668			19,668		19,668
Net loss attributable to noncontrolling interests and deconsolidation of noncontrolling interest	56						56
Unrealized gain (loss) on interest rate hedges	1,808				1,808	1,808
Distributions to noncontrolling interests	(4,199)		(3,128)			(3,128)	(1,071)
Contributions from noncontrolling interest	376						376
Dividends	(92,834)			(92,834)		(92,834)
Stock issued during period (in shares)		3,587
Equity offerings, net of issuance costs	113,194	$ 36	113,158			113,194
Shares issued under Dividend Reinvestment Program (in shares)		80
Shares issued under Dividend Reinvestment Program	2,576	$ 1	2,575			2,576
Share grants, net of share grant amortization and forfeitures (in shares)		237
Share grants, net of share grant amortization and forfeitures	2,741	$ 2	2,739			2,741
Balance, shares at Dec. 31, 2017		78,510
Balance at Dec. 31, 2017	$ 1,095,336	$ 785	$ 1,483,980	$ (399,213)	$ 9,419	$ 1,094,971	$ 365

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net income	$ 19,612	$ 119,288	$ 89,187
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on sale of real estate	24,915	101,704	91,107
Depreciation and amortization	112,056	108,406	108,935
Provision for losses on accounts receivable	882	1,706	1,368
Deferred tax benefit	(84)	(698)	0
Real estate impairment and casualty (gain), net	33,152	(676)	5,909
Share-based compensation expense	4,771	3,491	5,112
Amortization of debt premiums, discounts and related financing costs	1,897	3,187	3,486
Loss on extinguishment of debt, net	0	0	119
Changes in other assets	(20,199)	(15,713)	(10,496)
Changes in other liabilities	3,454	(2,562)	(3,195)
Net cash provided by operating activities	130,626	114,725	109,318
Cash flows from investing activities
Real estate acquisitions, net	(138,371)	(227,413)	(151,917)
Capital improvements to real estate	(60,515)	(57,094)	(41,507)
Development in progress	(18,150)	(22,572)	(31,203)
Net cash received from sale of real estate	30,798	243,624	136,930
Real estate deposits, net	6,250	0	0
Insurance proceeds	0	883	0
Non-real estate capital improvements	(3,866)	(920)	(2,129)
Net cash used in investing activities	(196,354)	(63,492)	(89,826)
Cash flows from financing activities
Line of credit borrowings, net	46,000	15,000	55,000
Principal payments – mortgage notes payable	(52,571)	(270,061)	(4,512)
Borrowing under construction loan	0	0	4,558
Notes payable repayments	0	0	(150,000)
Proceeds from dividend reinvestment program	2,576	700	0
Proceeds from term loan	50,000	100,000	150,000
Payment of financing costs	(319)	(1,590)	(5,095)
Dividends paid	(91,666)	(85,648)	(61,510)
Contributions from noncontrolling interests	0	0	5
Distributions to noncontrolling interests	(4,199)	(196)	0
Net proceeds from equity offerings	113,194	172,936	5,215
Payment of tax withholdings for restricted share awards	(2,286)	(1,960)	(2,071)
Net cash provided by (used in) financing activities	60,729	(70,819)	(8,410)
Net (decrease) increase in cash, cash equivalents and restricted cash	(4,999)	(19,586)	11,082
Cash, cash equivalents and restricted cash at beginning of year	17,622	37,208	26,126
Cash, cash equivalents and restricted cash at end of year	12,623	17,622	37,208
Supplemental disclosure of cash flow information:
Cash paid for interest, net of capitalized interest expense	45,730	51,054	57,179
Cash paid for income taxes	17	65	261
Change in accrued capital improvements and development costs	3,264	(3,788)	(4,229)
Reconciliation of cash, cash equivalents and restricted cash:
Cash, cash equivalents and restricted cash	$ 17,622	$ 37,208	$ 26,126

Nature of Business

Nature of Business	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature Of Business	NATURE OF BUSINESS Washington Real Estate Investment Trust (“Washington REIT”), a Maryland real estate investment trust, is a self-administered equity real estate investment trust, successor to a trust organized in 1960. Our business consists of the ownership and operation of income-producing real estate properties in the greater Washington Metro region. We own a diversified portfolio of office buildings, multifamily buildings and retail centers. Federal Income Taxes We believe that we qualify as a REIT under Sections 856-860 of the Internal Revenue Code of 1986, as amended (the "Code"), and intend to continue to qualify as such. We have considered the provisions of the Tax Cuts and Jobs Act (the "TCJA"), which was signed into law on December 22, 2017 and which generally takes effect for taxable years beginning on or after January 1, 2018, and do not expect the TCJA to have a material impact on our ability to continue to qualify as a REIT. To maintain our status as a REIT, we are, among other things, required to distribute 90% of our REIT taxable income (which is, generally, our ordinary taxable income, with certain modifications), excluding any net capital gains and any deductions for dividends paid to our shareholders on an annual basis. When selling a property, we generally have the option of (a) reinvesting the sales proceeds of property sold, in a way that allows us to defer recognition of some or all taxable gain realized on the sale, (b) distributing gains to the shareholders with no tax to us or (c) treating net long-term capital gains as having been distributed to our shareholders, paying the tax on the gain deemed distributed and allocating the tax paid as a credit to our shareholders. During the three years ended December 31, 2017 , we sold our interests in the following properties (in thousands): Disposition Date Property Type Gain on Sale October 23, 2017 Walker House Apartments Multifamily $ 23,838 Total 2017 $ 23,838 May 26, 2016 Dulles Station II (1) Office $ 527 June 27, 2016 Maryland Office Portfolio Transaction I (2) Office 23,585 September 22, 2016 Maryland Office Portfolio Transaction II (3) Office 77,592 Total 2016 $ 101,704 March 20, 2015 Country Club Towers Multifamily $ 30,277 September 9, 2015 1225 First Street (4) Multifamily — October 21, 2015 Munson Hill Towers Multifamily 51,395 December 14, 2015 Montgomery Village Center Retail 7,981 Total 2015 $ 89,653 (1) Land held for future development and an interest in a parking garage. (2) Maryland Office Portfolio Transaction I consists of 6110 Executive Boulevard, 600 Jefferson Plaza, Wayne Plaza and West Gude Drive. (3) Maryland Office Portfolio Transaction II consists of 51 Monroe Street and One Central Plaza. (4) Interest in land held for future development. The taxable gains for Walker House Apartments, Dulles Station II and the properties included in Maryland Office Portfolio Transaction I were distributed to shareholders through the quarterly dividends. The properties included in Maryland Office Portfolio Transaction II were identified for a reverse deferred exchange under Section 1031 of the Code. We acquired the replacement property, Riverside Apartments, during the second quarter of 2016 (see note 3, under "Acquisition"). We reinvested a portion of the Country Club Towers, Munson Hill Towers and Montgomery Village Center sales proceeds in replacement properties through deferred tax exchanges. Generally, and subject to our ongoing qualification as a REIT, no provisions for income taxes are necessary except for taxes on undistributed taxable income and taxes on the income generated by our taxable REIT subsidiaries (“TRSs”). Our TRSs are subject to corporate federal and state income tax on their taxable income at regular statutory rates, or as calculated under the alternative minimum tax, as appropriate. During the second quarter of 2016, we recognized an income tax benefit of $0.7 million from a reduction of the valuation allowance for a deferred tax asset at one of our taxable REIT subsidiaries. As of December 31, 2017 , a deferred tax asset of our TRSs of $1.4 million was fully reserved. As of December 31, 2016 , our TRSs had a deferred tax asset of $0.5 million , net of a valuation allowance of $2.9 million . As of December 31, 2017 and 2016 , our TRSs had deferred tax liabilities of $0.0 million and $0.4 million , respectively. Additionally, in connection with the acquisition of Watergate 600 (see note 3), we recorded a deferred state and local tax liability of approximately $0.6 million . These deferred tax liabilities are primarily related to temporary differences in the timing of the recognition of revenue, amortization and depreciation. The following is a breakdown of the taxable percentage of our dividends for the years ended December 31, 2017, 2016 and 2015 (unaudited): 2017 2016 2015 Ordinary income 76 % 66 % 78 % Return of capital — % 33 % 22 % Qualified dividends 2 % — % — % Unrecaptured Section 1250 gain 8 % 1 % — % Capital gain 14 % — % — %

Accounting Policies

Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND BASIS OF PRESENTATION Principles of Consolidation and Basis of Presentation The accompanying audited consolidated financial statements include the consolidated accounts of Washington REIT and our subsidiaries and entities in which Washington REIT has a controlling financial interest, including where Washington REIT has been determined to be a primary beneficiary of a variable interest entity (“VIE”). See note 3 for additional information on the properties for which there is a noncontrolling interest. All intercompany balances and transactions have been eliminated in consolidation. We have prepared the accompanying audited consolidated financial statements pursuant to the rules and regulations of the Securities and Exchange Commission. Use of Estimates in the Financial Statements The preparation of financial statements in conformity with Generally Accepted Accounting Principles ("GAAP") requires management to make certain 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. Recent Accounting Pronouncements Pronouncements Adopted In November 2016, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) 2016-18, Statement of Cash Flows (Topic 230) - Restricted Cash , which requires that restricted cash and cash equivalents be included with cash and cash equivalents when reconciling beginning-of-period and end-of-period total amounts shown on the consolidated statements of cash flows. The new standard is effective for public entities for fiscal years beginning after December 15, 2017 and for interim periods therein, with early adoption permitted. We adopted ASU 2016-18 as of December 31, 2017. The impact of the implementation was as follows: Year Ended December 31, 2017 2016 2015 Net cash provided by operating activities (prior to adoption of ASU 2016-18) $ 130,715 $ 116,931 $ 109,426 Impact of including restricted cash with cash and cash equivalents (89 ) (2,206 ) (108 ) Net cash provided by operating activities (after adoption of ASU 2016-18) $ 130,626 $ 114,725 $ 109,318 Net cash used in investing activities (prior to adoption of ASU 2016-18) $ (192,902 ) $ (58,632 ) $ (93,018 ) Impact of including restricted cash with cash and cash equivalents (3,452 ) (4,860 ) 3,192 Net cash used in investing activities (after adoption of ASU 2016-18) $ (196,354 ) $ (63,492 ) $ (89,826 ) Pronouncements Not Yet Adopted In August 2017, the FASB 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. The transition guidance provides companies with the option of early adopting the new standard using a modified retrospective transition method in any interim period after issuance of the update, or alternatively requires adoption for fiscal years beginning after December 15, 2018. We adopted the new standard as of January 1, 2018 and adoption does not have a material impact on our consolidated financial statements. In May 2017, the FASB issued ASU 2017-09, Compensation - Stock Compensation (Topic 718) - Scope of Modification Accounting, which provides guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting. The new standard is effective for all entities for fiscal years beginning after December 15, 2017 and for interim periods therein, with early adoption permitted. We adopted the new standard as of January 1, 2018 and adoption does not have a material impact on our consolidated financial statements. In August 2016, the FASB issued ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments , which provides specific guidance on how cash receipts and payments should be presented and classified in the statement of cash flows for eight specific issues. The new standard is effective for public entities for fiscal years beginning after December 15, 2017 and for interim periods therein, with early adoption permitted. We adopted the new standard as of January 1, 2018 and adoption does not have a material impact on our consolidated financial statements. In June 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”), which creates a single source of revenue guidance. The new standard provides accounting guidance for all revenue arising from contracts with customers and affects all entities that enter into contracts to provide goods or services to their customers (unless the contracts are in the scope of other U.S. generally accepted accounting principles (“GAAP”) requirements, such as the leasing literature). The guidance also provides a model for the measurement and recognition of gains and losses on the sale of certain nonfinancial assets, such as property and equipment, including real estate. The new standard is effective for public entities for fiscal years beginning after December 15, 2017 and for interim periods therein. We adopted the new standard for the fiscal year beginning on January 1, 2018. We evaluated the requirements for recognition of revenue from contracts with customers and measuring gains and losses on the sale of properties in accordance with ASU 2014-09 and concluded that adoption of the new standard will not impact the amount or timing of our revenue recognition. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) (“ASU 2016-02”) , which amends existing accounting standards for lease accounting, including by requiring lessees to recognize most leases on the balance sheet and making certain changes to lessor accounting. The new standard is effective for public entities for fiscal years beginning after December 15, 2018 and for interim periods therein with early adoption permitted. Upon adoption, for leases in which we are the lessor, the lease contract will be separated into lease and non-lease components in accordance with the provisions outlined within ASU 2014-09. The lease component of the contract will be recognized on a straight-line basis in accordance with ASU 2016-02, while the non-lease component will be recognized under the provisions of ASU 2014-09. For lease contracts with a duration of more than one year in which we are the lessee, the present value of future lease payments will be recognized on our balance sheet as a right-of-use asset and a corresponding lease liability. Also, only direct leasing costs may be capitalized under the new standard, while current accounting standards allow for the capitalization of indirect leasing costs. We are currently evaluating the impact ASU 2016-02 may have on Washington REIT’s consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, Measurement of Credit Losses on Financial Instruments , which requires financial assets measured at an amortized cost basis, including trade receivables, to be presented at the net amount expected to be collected. The new standard is effective for public entities for fiscal years beginning after December 15, 2019 and for interim periods therein with adoption one year earlier permitted. We are currently evaluating the impact the new standard may have on Washington REIT’s consolidated financial statements. Revenue Recognition We lease multifamily properties under operating leases with terms of generally one year or less. We lease commercial properties (our office and retail segments) under operating leases with an average term of seven years. Substantially all commercial leases contain fixed escalations or, in some instances, changes based on the Consumer Price Index, which occur at specified times during the term of the lease. We recognize rental income and rental abatements from our multifamily and commercial leases when earned on a straight-line basis over the lease term. Recognition of rental income commences when control of the leased space has been given to the tenant. We recognize sales of real estate at closing only when sufficient down payments have been obtained, possession and other attributes of ownership have been transferred to the buyer and we have no significant continuing involvement. We recognize cost reimbursement income from pass-through expenses on an accrual basis over the periods in which the expenses were incurred. Pass-through expenses are comprised of real estate taxes, operating expenses and common area maintenance costs which are reimbursed by tenants in accordance with specific allowable costs per tenant lease agreements. Parking revenues are derived from leases, monthly parking agreements and transient parking. We recognize parking revenues from leases on a straight-line basis over the lease term and other parking revenues as earned. Accounts Receivable and Allowance for Doubtful Accounts Accounts receivable primarily represents amounts accrued and unpaid from tenants in accordance with the terms of the respective leases, subject to our revenue recognition policy. We review receivables monthly and establish reserves when, in the opinion of management, collection of the receivable is doubtful. We establish reserves for tenants whose rent payment histories or financial conditions cast doubt upon the tenants’ abilities to perform under their lease obligations. When we determine the collection of a receivable to be doubtful in the same quarter that we established the receivable, we recognize the allowance for that receivable as an offset to real estate revenues. When we determine a receivable that was initially established in a prior quarter to be doubtful, we recognize the allowance as an operating expense in Real estate expenses in the consolidated statements of income. In addition to rents due currently, accounts receivable include amounts representing minimal rental income accrued on a straight-line basis to be paid by tenants over the remaining term of their respective leases. Our accounts receivable balances include $0.4 million and $2.4 million of notes receivable as of December 31, 2017 and 2016 , respectively. The decrease is due to the repayment during the fourth quarter of 2017 of a note receivable acquired in 2008 with the purchase of 2445 M Street. Debt Issuance Costs We amortize external debt issuance costs using the effective interest rate method or the straight-line method which approximates the effective interest rate method, over the estimated life of the related debt. We record debt issuance costs related to notes and mortgage notes, net of amortization, on our consolidated balance sheets as an offset to their related debt. We record debt issuance costs related to revolving lines of credit on our consolidated balance sheets with Prepaid expenses and other assets, regardless of whether a balance on the line of credit is outstanding. We record the amortization of all debt issuance costs as interest expense. Deferred Leasing Costs We capitalize and amortize costs associated with the successful negotiation of leases, both external commissions and internal direct costs, on a straight-line basis over the terms of the respective leases. We record the amortization of deferred leasing costs in Depreciation and amortization on the consolidated statements of income. If an applicable lease terminates prior to the expiration of its initial lease term, we write off the carrying amount of the costs to amortization expense. We capitalize and amortize against revenue leasing incentives associated with the successful negotiation of leases on a straight-line basis over the terms of the respective leases. We record the amortization of deferred leasing incentives as a reduction of revenue. If an applicable lease terminates prior to the expiration of its initial lease term, we write off the carrying amount of the costs as a reduction of revenue. Real Estate and Depreciation We depreciate buildings on a straight-line basis over estimated useful lives ranging from 28 to 50 years. We capitalize all capital improvements associated with replacements, improvements or major repairs to real property that extend its useful life and depreciate them using the straight-line method over their estimated useful lives ranging from 3 to 30 years. We also capitalize costs incurred in connection with our development projects, including capitalizing interest incurred on borrowing obligations and other internal costs during periods in which qualifying expenditures have been made and activities necessary to get the development projects ready for their intended use are in progress. Capitalization of these costs begin when the activities and related expenditures commence and cease when the project is substantially complete and ready for its intended use, at which time the project is placed in service and depreciation commences. In addition, we capitalize tenant leasehold improvements when certain criteria are met, including when we supervise construction and will own the improvements. We depreciate all tenant improvements over the shorter of the useful life of the improvements or the term of the related tenant lease. Real estate depreciation expense from continuing operations was $90.1 million , $84.1 million , $80.7 million during the years ended December 31, 2017 , 2016 and 2015 , respectively. We charge maintenance and repair costs that do not extend an asset’s useful life to expense as incurred. Interest expense and interest capitalized to real estate assets related to development and major renovation activities for the three years ended December 31, 2017 were as follows (in thousands): Year Ended December 31, 2017 2016 2015 Total interest incurred $ 48,498 $ 53,794 $ 60,204 Capitalized interest (964 ) (668 ) (658 ) Interest expense, net of capitalized interest $ 47,534 $ 53,126 $ 59,546 We recognize impairment losses on long-lived assets used in operations, development assets or land held for future development, if indicators of impairment are present and the net undiscounted cash flows estimated to be generated by those assets are less than the assets' carrying amount and estimated undiscounted cash flows associated with future development expenditures. If such carrying amount is in excess of the estimated undiscounted cash flows from the operation and disposal of the property, we would recognize an impairment loss equivalent to an amount required to adjust the carrying amount to its estimated fair value, calculated in accordance with current GAAP fair value provisions. Assets held for sale are recorded at the lower of cost or fair value less costs to sell. Acquisitions The properties we acquire typically are not businesses as defined by ASU 2017-01, Business Combinations (Topic 805) - Clarifying the Definition of a Business . Per this definition, a set of transferred assets and activities is not a business when substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or group of similar identifiable assets. We therefore account for such acquisitions as asset acquisitions. Acquisition costs are capitalized and identifiable assets (including physical assets and in-place leases), liabilities assumed and any noncontrolling interests are measured by allocating the cost of the acquisition on a relative fair value basis. Acquisitions executed prior to our adoption of ASU 2017-01 as of January 1, 2017 were accounted for as business combinations. We determine the fair values of acquired buildings on an “as-if-vacant” basis considering a variety of factors, including the replacement cost of the property, estimated rental and absorption rates, estimated future cash flows and valuation assumptions consistent with current market conditions. We determine the fair value of land acquired based on comparisons to similar properties that have been recently marketed for sale or sold. The fair value of in-place leases consists of the following components – (a) the estimated cost to us to replace the leases, including foregone rents during the period of finding a new tenant and foregone recovery of tenant pass-throughs (referred to as “absorption cost”); (b) the estimated cost of tenant improvements, and other direct costs associated with obtaining a new tenant (referred to as “tenant origination cost”); (c) estimated leasing commissions associated with obtaining a new tenant (referred to as “leasing commissions”); (d) the above/at/below market cash flow of the leases, determined by comparing the projected cash flows of the leases in place, including consideration of renewal options, to projected cash flows of comparable market-rate leases (referred to as “net lease intangible”); and (e) the value, if any, of customer relationships, determined based on our evaluation of the specific characteristics of each tenant’s lease and our overall relationship with the tenant (referred to as “customer relationship value”). We have attributed no value to customer relationships as of December 31, 2017 and 2016 . We discount the amounts used to calculate net lease intangibles using an interest rate which reflects the risks associated with the leases acquired. We classify tenant origination costs as income producing property on our consolidated balance sheets and amortize the tenant origination costs as depreciation expense on a straight-line basis over the remaining life of the underlying leases. We classify leasing commissions and absorption costs as other assets and amortize leasing commissions and absorption costs as amortization expense on a straight-line basis over the remaining life of the underlying leases. We classify net lease intangible assets as other assets and amortize them on a straight-line basis as a decrease to real estate rental revenue over the remaining term of the underlying leases. We classify net lease intangible liabilities as other liabilities and amortize them on a straight-line basis as an increase to real estate rental revenue over the remaining term of the underlying leases. If any of the fair value of below market lease intangibles includes fair value associated with a renewal option, such amounts are not amortized until the renewal option is executed, else the related value is expensed at that time. Should a tenant terminate its lease, we accelerate the amortization of the unamortized portion of the tenant origination cost, leasing commissions, absorption costs and net lease intangible associated with that lease, over its new, shorter term. Balances, net of accumulated depreciation or amortization, as appropriate, of the components of the fair value of in-place leases at December 31, 2017 and 2016 were as follows (in thousands): December 31, 2017 2016 Gross Carrying Value Accumulated Amortization Net Gross Carrying Value Accumulated Amortization Net Tenant origination costs $ 66,378 $ 50,157 $ 16,221 $ 54,352 $ 44,823 $ 9,529 Leasing commissions/absorption costs 123,992 95,115 28,877 101,311 86,210 15,101 Net lease intangible assets 19,362 16,089 3,273 18,903 14,193 4,710 Net lease intangible liabilities 43,230 28,174 15,056 33,687 25,359 8,328 Below-market ground lease intangible asset 12,080 1,903 10,177 12,080 1,714 10,366 Amortization of these combined components during the three years ended December 31, 2017 , 2016 and 2015 was as follows (in thousands): Year Ended December 31, 2017 2016 2015 Depreciation and amortization expense $ 14,911 $ 17,655 $ 22,244 Real estate rental revenue (increase) decrease, net (922 ) 410 538 $ 13,989 $ 18,065 $ 22,782 Amortization of these combined components over the next five years is projected to be as follows (in thousands): Depreciation and amortization expense Real estate rental revenue, net increase Total 2018 $ 13,456 $ (1,574 ) $ 11,882 2019 6,485 (1,633 ) 4,852 2020 4,905 (1,335 ) 3,570 2021 3,729 (1,191 ) 2,538 2022 3,058 (1,155 ) 1,903 Thereafter 23,642 (4,895 ) 18,747 Software Developed for Internal Use The costs of software developed for internal use that qualify for capitalization are included with Prepaid expenses and other assets on our consolidated balance sheets. These capitalized costs include external direct costs utilized in developing or obtaining the applications and expenses for employees who are directly associated with the development of the applications. Capitalization of such costs begins when the preliminary project stage is complete and continues until the project is substantially complete and is ready for its intended purpose. Completed projects are amortized on a straight-line basis over their estimated useful lives. Discontinued Operations We classify properties as held for sale when they meet the necessary criteria, which include: (a) senior management commits to and actively embarks upon a plan to sell the assets, (b) the sale is expected to be completed within one year under terms usual and customary for such sales and (c) actions required to complete the plan indicate that it is unlikely that significant changes to the plan will be made or that the plan will be withdrawn. We generally consider that a property has met these criteria when a sale of the property has been approved by the board of trustees, or a committee with authorization from the board of trustees, there are no known significant contingencies related to the sale and management believes it is probable that the sale will be completed within one year. Depreciation on these properties is discontinued at the time they are classified as held for sale, but operating revenues, operating expenses and interest expense continue to be recognized until the date of sale. Revenues and expenses of properties that are either sold or classified as held for sale are presented as discontinued operations for all periods presented in the consolidated statements of income if the dispositions represent a strategic shift that has (or will have) a major effect on our operations and financial results. Interest on debt that can be identified as specifically attributed to these properties is included in discontinued operations. If the dispositions do not represent a strategic shift that has (or will have) a major effect on our operations and financial results, then the revenues and expenses of the properties that are classified as sold or held for sale are presented as continuing operations in the consolidated statements of income for all periods presented. Segments We evaluate performance based upon net operating income from the combined properties in each segment. Our reportable operating segments are consolidations of similar properties. GAAP requires that segment disclosures present the measure(s) used by the chief operating decision maker for purposes of assessing segments’ performance. Net operating income is a key measurement of our segment profit and loss. Net operating income is defined as segment real estate rental revenue less segment real estate expenses. Cash and Cash Equivalents Cash and cash equivalents include cash and commercial paper with original maturities of 90 days or less. We maintain cash deposits with financial institutions that at times exceed applicable insurance limits. We reduce this risk by maintaining such deposits with high quality financial institutions that management believes are credit-worthy. Restricted Cash Restricted cash includes funds escrowed for tenant security deposits, real estate tax, insurance and mortgage escrows and escrow deposits required by lenders on certain of our properties to be used for future building renovations or tenant improvements. Earnings Per Common Share We determine “Basic earnings per share” using the two-class method as our unvested restricted share awards and units have non-forfeitable rights to dividends, and are therefore considered participating securities. We compute basic earnings per share by dividing net income attributable to the controlling interest less the allocation of undistributed earnings to unvested restricted share awards and units by the weighted-average number of common shares outstanding for the period. We also determine “Diluted earnings per share” under the two-class method with respect to the unvested restricted share awards. We further evaluate any other potentially dilutive securities at the end of the period and adjust the basic earnings per share calculation for the impact of those securities that are dilutive. Our dilutive earnings per share calculation includes the dilutive impact of employee stock options based on the treasury stock method and our performance share units under the contingently issuable method. Stock Based Compensation We currently maintain equity based compensation plans for trustees, officers and employees. We recognize compensation expense for service-based share awards ratably over the period from the service inception date through the vesting period based on the fair market value of the shares on the date of grant. If an award's service inception date precedes the grant date, we initially measure compensation expense for awards with performance conditions at fair value at the service inception date based on probability of payout, and we remeasure compensation expense at subsequent reporting dates until all of the award’s key terms and conditions are known and the grant date is established. We amortize awards with performance conditions using the graded expense method. We measure compensation expense for awards with market conditions based on the grant date fair value, as determined using a Monte Carlo simulation, and we amortize the expense ratably over the requisite service period, regardless of whether the market conditions are achieved and the awards ultimately vest. Compensation expense for the trustee grants, which fully vest immediately, is fully recognized upon issuance based upon the fair market value of the shares on the date of grant. Accounting for Uncertainty in Income Taxes We can recognize a tax benefit only if it is “more likely than not” that a particular tax position will be sustained upon examination or audit. To the extent that the “more likely than not” standard has been satisfied, the benefit associated with a tax position is measured as the largest amount that is greater than 50% likely of being recognized upon settlement. As of December 31, 2017 and 2016, we did not have any unrecognized tax benefits. We do not believe that there will be any material changes to our uncertain tax positions over the next twelve months. We are subject to federal income tax as well as income tax of the states of Maryland and Virginia, and the District of Columbia. However, as a REIT, we generally are not subject to income tax on our taxable income to the extent it is distributed as dividends to our shareholders. Tax returns filed for 2013 through 2017 tax years are subject to examination by taxing authorities. We classify interest and penalties related to uncertain tax positions, if any, in our financial statements as a component of general and administrative expense. Derivatives We borrow funds at a combination of fixed and variable rates. Borrowings under our revolving credit facility and term loans bear interest at variable rates. Our interest rate risk management objectives are to minimize interest rate fluctuation on long-term indebtedness and limit the impact of interest rate changes on earnings and cash flows. To achieve these objectives, from time to time, we may enter into interest rate hedge contracts such as collars, swaps, caps and treasury lock agreements in order to mitigate our interest rate risk with respect to various debt instruments. We generally do not hold or issue these derivative contracts for trading or speculative purposes. The interest rate swaps we enter into are recorded at fair value on a recurring basis. We assess effectiveness of our cash flow hedges both at inception and on an ongoing basis. The effective portion of changes in fair value of the interest rate swaps associated with our cash flow hedges is recorded in accumulated other comprehensive income (loss). Our cash flow hedges become ineffective if critical terms of the hedging instrument and the debt instrument such as notional amounts, settlement dates, reset dates, calculation period and LIBOR do not perfectly match. In addition, we evaluate the default risk of the counterparty by monitoring the creditworthiness of the counterparty. When ineffectiveness of a cash flow hedge exists, the ineffective portion of changes in fair value of the interest rate swaps associated with our cash flow hedges is recognized in earnings in the period affected.

Real Estate

Real Estate	12 Months Ended
	Dec. 31, 2017
Real Estate [Abstract]
Real Estate Investment	REAL ESTATE As of December 31, 2017 and 2016 , our real estate investment portfolio classified as held and used, at cost, consists of properties as follows (in thousands): December 31, 2017 2016 Office $ 1,355,033 $ 1,349,378 Multifamily 895,811 885,084 Retail 451,158 450,941 $ 2,702,002 $ 2,685,403 Our results of operations are dependent on the overall economic health of our markets, tenants and the specific segments in which we own properties. These segments include office, retail and multifamily. All segments are affected by external economic factors, such as inflation, consumer confidence and unemployment rates, as well as changing tenant and consumer requirements. As of December 31, 2017 , no property accounted for more than 10% of total assets. No single property or tenant accounted for more than 10% of the real estate rental revenue. We have properties under development/redevelopment and held for current or future development as of December 31, 2017 and 2016. In the office segment, we had a redevelopment project at the Army Navy Building, an office property in Washington, DC, to upgrade its common areas and add significant amenities in order to make the property more competitive within its sub-market. As of December 31, 2017 , we had invested $4.8 million in the redevelopment and placed substantially all of the project into service. In the multifamily segment, we have The Trove, a multifamily development adjacent to The Wellington, and own land held for future multifamily development adjacent to Riverside Apartments. As of December 31, 2017 , we had invested $29.7 million and $19.2 million , including the costs of acquired land, in the Trove and the development adjacent to Riverside Apartments, respectively. In the retail segment, we currently have a redevelopment project to add rentable space at Spring Valley Village. As of December 31, 2017 , we had invested $3.6 million in the redevelopment. The cost of our real estate portfolio under development or held for future development as of December 31, 2017 and 2016 is as follows (in thousands): December 31, 2017 2016 Office $ 680 $ 2,640 Multifamily 49,616 36,013 Retail 4,126 1,579 $ 54,422 $ 40,232 Acquisitions Our current strategy is to recycle legacy assets that lack the income growth potential we seek and to invest in high-quality assets with compelling value-add returns through redevelopment opportunities in our existing portfolio and acquisitions that meet our stringent investment criteria. We focus on properties inside the Washington metro region’s Beltway, near major transportation nodes and in areas with strong employment drivers and superior growth demographics. Properties and land for development acquired during the three years ended December 31, 2017 were as follows: Acquisition Date Property Type # of units (unaudited) Rentable Square Feet (unaudited) Contract Purchase Price (in thousands) April 4, 2017 Watergate 600 Office N/A 293,000 $ 135,000 May 20, 2016 Riverside Apartments Multifamily 1,222 N/A $ 244,750 July 1, 2015 The Wellington Multifamily 711 N/A $ 167,000 The results of operations from acquired operating properties are included in the consolidated statements of income as of their acquisition dates. The revenue and earnings of our acquisitions during their year of acquisition for the three years ended December 31, 2017 are as follows (in thousands): Year Ended December 31, 2017 2016 2015 Real estate rental revenue $ 14,518 $ 13,112 $ 6,797 Net income (loss) 2,226 (1,688 ) (2,748 ) As discussed in note 2 , we record the acquired physical assets (land, building and tenant improvements), in-place leases (absorption, tenant origination costs, leasing commissions, and net lease intangible assets/liabilities), and any other liabilities on a relative fair value basis. We recorded the total cost of the above acquisitions as follows (in thousands): 2017 2016 2015 Land $ 45,981 $ 38,924 $ 30,548 Land held for development — 15,968 15,000 Buildings 66,241 184,854 116,563 Tenant origination costs 12,084 — — Leasing commissions/absorption costs 23,161 4,992 4,889 Net lease intangible assets 498 22 — Net lease intangible liabilities (9,585 ) (10 ) — Deferred tax liability (560 ) — — Total $ 137,820 $ 244,750 $ 167,000 The weighted remaining average life for 2017 acquisition components above, other than land and building, are 89 months for tenant origination costs, 82 months for leasing commissions/absorption costs, 13 months for net lease intangible assets and 102 months for net lease intangible liabilities. The difference in the total contract purchase price of $135.0 million for the 2017 acquisition and cash paid for the acquisition per the consolidated statements of cash flows of $138.4 million is primarily due to capitalized acquisition-related costs ( $2.8 million ) and a net credit to the buyer for certain expenditures ( $1.0 million ), partially offset by the issuance of 12,124 operating partnership units (“Operating Partnership Units”) as part of the consideration ( $0.4 million ). The Operating Partnership Units are units in WashREIT Watergate 600 OP LP, a consolidated subsidiary of Washington REIT. These Operating Partnership Units may be redeemed for either cash equal to the fair market value of a share of Washington REIT common stock at the time of redemption (based on a 20 -day average price) or, at the option of Washington REIT, one registered or unregistered share of Washington REIT common stock. In connection with the 2017 acquisition, we granted registration rights to the two contributors of the Watergate 600 property relating to the resale of any shares issued upon exchange of Operating Partnership Units pursuant to a shelf registration statement that we have an obligation to make available to the contributors approximately one year after the issuance of the Operating Partnership Units. The difference in the total contract price of $244.8 million for the 2016 acquisition and cash paid for the acquisition per the consolidated statements of cash flows of $227.4 million is primarily due to acquisition of land for development of $16.0 million and credits received at settlement totaling $1.4 million . The difference in the total contract price of $167.0 million for the 2015 acquisitions and cash paid for the acquisitions per the consolidated statements of cash flows of $151.9 million is primarily due to acquisition of land for development of $15.0 million and credits received at settlement totaling $0.1 million . Variable Interest Entities In November 2011, we executed a joint venture operating agreement with a real estate development company to develop a high-rise multifamily property at 1225 First Street in Alexandria, Virginia. Washington REIT and the real estate development company owned 95% and 5% of the joint venture, respectively. During the second quarter of 2015, we determined that we would not develop the property and began negotiations to sell our interest in the joint venture. We recognized a $5.9 million impairment charge for the second quarter of 2015 in order to reduce the carrying value of the property to its estimated fair value. We based this fair value on the contract sale price in the purchase and sale agreement. This fair valuation falls into Level 2 of the fair value hierarchy. During the third quarter of 2015, we sold our 95% interest in the joint venture for a contract sale price of $14.5 million and deconsolidated the entity, as this joint venture had previously been consolidated as Washington REIT was the primary beneficiary of the VIE. In June 2011, we executed a joint venture operating agreement with a real estate development company to develop The Maxwell, a mid-rise multifamily property in Arlington, Virginia. Major construction activities at The Maxwell ended during December 2014, and the building became available for occupancy during the first quarter of 2015. Washington REIT was the 90% owner of the joint venture. The real estate development company owned 10% of the joint venture and was responsible for the development and construction of the property. During the fourth quarter of 2017, we purchased the 10% joint venture interest from the real estate development company for a contract purchase price of $4.1 million . Upon the completion of this transaction, the joint venture ended and Washington REIT became sole owner of The Maxwell. We determined that, prior to completion of this transaction, The Maxwell joint venture was a VIE primarily based on the fact that the equity investment at risk was not sufficient to permit the entity to finance its activities without additional financial support. We also determined that Washington REIT was the primary beneficiary of the VIE due to the fact that Washington REIT was determined to have a controlling financial interest in the entity. In January 2016, Washington REIT exercised its right to purchase at par The Maxwell’s construction loan from the original third-party lender. Upon the purchase, the construction loan became an intercompany loan payable from the consolidated VIE to Washington REIT that is eliminated in consolidation. The intercompany loan payable was extinguished as part of Washington REIT’s purchase of the joint venture partner’s 10% interest during the fourth quarter of 2017. We include joint venture land acquisitions and related capitalized development costs on our consolidated balance sheets in properties under development or held for future development until placed in service or sold. The Maxwell was placed into service during the fourth quarter of 2014 and first quarter of 2015. As of December 31, 2016 , The Maxwell joint venture's assets were as follows (in thousands): December 31, 2016 Land $ 12,851 Income producing property 37,949 Accumulated depreciation and amortization (4,571 ) Other assets 456 $ 46,685 As of December 31, 2016 , The Maxwell joint venture's liabilities were as follows (in thousands): December 31, 2016 Mortgage notes payable, net (1) $ 31,869 Accounts payable and other liabilities 186 Tenant security deposits 99 $ 32,154 (1) The mortgage notes payable balance as of December 31, 2016 was eliminated in consolidation due to the purchase of the loan by Washington REIT in January 2016. The mortgage note payable was extinguished during the fourth quarter of 2017 due to Washington REIT’s purchase of the joint venture partner's interest. Properties Sold and Held for Sale We intend to hold our properties for investment with a view to long-term appreciation, to engage in the business of acquiring, developing and owning our properties, and to make occasional sales of the properties that no longer meet our long-term strategy or return objectives and where market conditions for sale are favorable. The proceeds from the sales may be reinvested into other properties, used to fund development operations or to support other corporate needs, or distributed to our shareholders. Depreciation on these properties is discontinued when classified as held for sale, but operating revenues, other operating expenses and interest continue to be recognized until the date of sale. During the second quarter of 2017, we executed a purchase and sale agreement for the sale of Walker House Apartments, a 212 unit multifamily property in Gaithersburg, Maryland, for a contract sale price of $32.2 million . We closed on the sale during the fourth quarter of 2017, recognizing a gain on sale of $23.8 million . During the fourth quarter of 2017, we executed a purchase and sale agreement for the sale of Braddock Metro Center, a 356,000 square foot office property in Alexandria, Virginia for a contract sale price of $93.0 million , and closed on the sale in January 2018. We determined that the property met the criteria for classification as held for sale as of December 31, 2017. Due to the negotiations to sell the property, we evaluated Braddock Metro Center for impairment and recognized a $9.1 million impairment charge during 2017 in order to reduce the carrying value of the property to its estimated fair value, less selling costs. We based this fair valuation on the expected sale price from a potential sale. There are few observable market transactions for similar properties. This fair valuation falls into Level 2 of the fair value hierarchy due to its reliance on a quoted price in a market that is not active. During the fourth quarter of 2017, we marketed for sale 2445 M Street, a 292,000 square foot office property in Washington, DC. The property did not meet the criteria for classification as held for sale as of December 31, 2017. Due to the negotiations to sell the property, we evaluated 2445 M Street for impairment and recognized a $24.1 million impairment charge during 2017 in order to reduce the carrying value of the property to its estimated fair value. We based this fair valuation on the expected sale price from a potential sale. There are few observable market transactions for similar properties. This fair valuation falls into Level 2 of the fair value hierarchy due to its reliance on a quoted price in a market that is not active. On January 23, 2018, we executed a purchase and sale agreement to sell 2445 M Street for a contract sale price of $100.0 million . We anticipate settlement in the third quarter of 2018, however, there can be no assurances that this proposed sale will be consummated. Upon execution of the purchase and sale agreement, the property met the criteria for classification as held for sale. During the second quarter of 2016, we sold Dulles Station, Phase II, which consists of land held for future development and an interest in a parking garage in Herndon, Virginia, for $12.1 million . Also during the second quarter of 2016, we executed two purchase and sale agreements with a single buyer for the sale of a portfolio of six office properties located in Maryland: 6110 Executive Boulevard, Wayne Plaza, 600 Jefferson Plaza, West Gude Drive, 51 Monroe Street and One Central Plaza (collectively, the "Maryland Office Portfolio") for an aggregate contract sale price of $240.0 million . We closed on the first sale transaction in June 2016 and closed on the second sale transaction in September 2016. We sold our interests in the following properties during the three years ended December 31, 2017 : Disposition Date Property Segment # of units (unaudited) Rentable Contract Gain on Sale October 23, 2017 Walker House Apartments Multifamily 212 N/A $ 32,200 $ 23,838 Total 2017 $ 32,200 $ 23,838 May 26, 2016 Dulles Station, Phase II (1) Office N/A N/A $ 12,100 $ 527 June 27, 2016 Maryland Office Portfolio Transaction I (2) Office N/A 692,000 111,500 23,585 September 22, 2016 Maryland Office Portfolio Transaction II (3) Office N/A 491,000 128,500 77,592 Total 2016 1,183,000 $ 252,100 $ 101,704 March 20, 2015 Country Club Towers Multifamily 227 N/A $ 37,800 $ 30,277 September 9, 2015 1225 First Street (4) Multifamily N/A N/A 14,500 — October 21, 2015 Munson Hill Towers Multifamily 279 N/A 57,050 51,395 December 14, 2015 Montgomery Village Center Retail N/A 197,000 27,750 7,981 Total 2015 506 197,000 $ 137,100 $ 89,653 (1) Land held for future development and an interest in a parking garage. (2) Maryland Office Portfolio Transaction I consists of 6110 Executive Boulevard, 600 Jefferson Plaza, Wayne Plaza and West Gude Drive. (3) Maryland Office Portfolio Transaction II consists of 51 Monroe Street and One Central Plaza. (4) Interest in land held for future development. We do not have significant continuing involvement in the operations of the disposed properties. While the Maryland Office Portfolio, in the aggregate, constitutes an individually significant disposition, it does not qualify for presentation and disclosure as a discontinued operation as it does not represent a strategic shift in our operations. Real estate rental revenue and net income for the Maryland Office Portfolio for the three years ended December 31, 2017 are as follows: Year Ending December 31, 2017 2016 2015 Real estate rental revenue $ — $ 20,266 $ 32,423 Net income — 9,376 9,848 Casualty Gains We recorded a net casualty gain of $0.7 million during the second quarter of 2016 associated with a fire at Bethesda Hill Towers that damaged four units, which is included in real estate impairment and casualty (gain), net on our consolidated statements of income. The net casualty gain is comprised of $0.9 million in third-party insurance proceeds received by us, which were partially offset by casualty charges of $0.2 million to write off the net book value of the damaged units at Bethesda Hill Towers.

Mortgage Notes Payable

Mortgage Notes Payable	12 Months Ended
	Dec. 31, 2017
Notes Payable, Noncurrent [Abstract]
Mortgage Notes Payable	MORTGAGE NOTES PAYABLE As of December 31, 2017 and 2016 , we had outstanding mortgage notes payable, each collateralized by one or more buildings and related land from our portfolio, as follows (in thousands): December 31, Properties Assumption/Issuance Date (1) Effective Interest Rate (2) 2017 2016 Payoff Date/Maturity Date Army Navy Building (3) 3/26/2014 3.18 % $ — $ 49,618 2/1/2017 Yale West (4) 2/21/2014 3.75 % 46,629 47,078 1/31/2022 Olney Village Center 8/30/2011 4.94 % 13,091 14,851 10/1/2023 Kenmore Apartments (5) 2/2/2009 5.37 % 32,194 32,938 9/1/2018 91,914 144,485 Premiums and discounts, net 3,385 4,354 Debt issuance costs, net (158 ) (299 ) $ 95,141 $ 148,540 (1) Each of these mortgages was assumed with the acquisition of the collateralized properties, except for the mortgage note secured by Kenmore Apartments, which was originally executed by Washington REIT. We record mortgages assumed in an acquisition at fair value. (2) Yield on the assumption/issuance date, including the effects of any premiums, discounts or fair value adjustments on the notes. (3) The note was prepaid without penalty in February 2017. (4) The maturity date of the mortgage note is January 1, 2052, but can be prepaid, without penalty, beginning on January 31, 2022. (5) The maturity date of the mortgage note is March 1, 2019, but can be prepaid, without penalty, beginning on September 1, 2018. Except as noted above, principal and interest are payable monthly until the maturity date, upon which all unpaid principal and interest are payable in full. Total cost basis of the above mortgaged properties was $208.3 million and $280.4 million at December 31, 2017 and 2016 , respectively. Scheduled principal payments subsequent to December 31, 2017 are as follows (in thousands): 2018 $ 34,544 2019 2,500 2020 2,659 2021 2,829 2022 46,984 Thereafter 2,398 $ 91,914

Unsecured Lines Of Credit Payab

Unsecured Lines Of Credit Payable	12 Months Ended
	Dec. 31, 2017
Unsecured Debt [Abstract]
Unsecured Lines Of Credit Payable	UNSECURED LINES OF CREDIT PAYABLE During the second quarter of 2015, we terminated our $100.0 million unsecured line of credit maturing in June 2015 and our $400.0 million unsecured line of credit maturing in July 2016 , and executed a new $600.0 million unsecured credit agreement ("Revolving Credit Facility") that matures in June 2019 , unless extended pursuant to one or both of the two six -month extension options. The Revolving Credit Facility has an accordion feature that allows us to increase the facility to $1.0 billion , subject to the extent the lenders agree to provide additional revolving loan commitments or term loans. In September 2015, we entered into a $150.0 million unsecured term loan ("2015 Term Loan") by executing a portion of the accordion feature under the Revolving Credit Facility. The 2015 Term Loan has a 5.5 year term and currently has an interest rate of one month LIBOR plus 110 basis points, based on Washington REIT's current unsecured debt ratings. We entered into two interest rate swaps to effectively fix the interest rate at 2.7% (see note 7 ). The amount of the Revolving Credit Facility unused and available at December 31, 2017 was as follows (in thousands): Committed capacity $ 600,000 Borrowings outstanding (166,000 ) Unused and available $ 434,000 We executed borrowings and repayments on the Revolving Credit Facility during 2017 as follows (in thousands): Balance at December 31, 2016 $ 120,000 Borrowings 274,000 Repayments (228,000 ) Balance at December 31, 2017 $ 166,000 The Revolving Credit Facility bears interest at a rate of either LIBOR plus a margin ranging from 0.875% to 1.55% or the base rate plus a margin ranging from 0% to 0.55% (in each case depending upon Washington REIT’s credit rating). The base rate is the highest of the administrative agent's prime rate, the federal funds rate plus 0.5% and the LIBOR market index rate plus 1.0% . As of December 31, 2017 , the interest rate on the facility is LIBOR plus 1.0% and the one month LIBOR was 1.56% . All outstanding advances for the Revolving Credit Facility are due and payable upon maturity in June 2019 , unless extended pursuant to one or both of the two six-month extension options. Interest only payments are due and payable generally on a monthly basis. In addition, the Revolving Credit Facility requires the payment of a facility fee ranging from 0.125% to 0.30% (depending on Washington REIT’s credit rating) on the $600.0 million committed capacity, without regard to usage. As of December 31, 2017 , the facility fee is 0.20% . For the three years ended December 31, 2017 , we recognized interest expense (excluding facility fees) and facility fees as follows (in thousands): Year Ended December 31, 2017 2016 2015 Interest expense (excluding facility fees) $ 3,857 $ 3,272 $ 2,266 Facility fees 1,217 1,220 1,241 The Revolving Credit Facility contains certain financial and non-financial covenants, all of which we have met as of December 31, 2017 and 2016 . Included in these covenants are limits on our total indebtedness, secured and unsecured indebtedness and required debt service payments. Information related to revolving credit facilities for the three years ended December 31, 2017 as follows (in thousands, except percentage amounts): Year Ended December 31, 2017 2016 2015 Total revolving credit facilities at December 31 $ 600,000 $ 600,000 $ 600,000 Borrowings outstanding at December 31 166,000 120,000 105,000 Weighted average daily borrowings during the year 179,633 214,962 167,573 Maximum daily borrowings during the year 252,000 358,000 350,000 Weighted average interest rate during the year 2.15 % 1.52 % 1.35 % Weighted average interest rate on borrowings outstanding at December 31 2.54 % 1.64 % 1.36 % The covenants under our Revolving Credit Facility require us to insure our properties against loss or damage in amounts customarily maintained by similar businesses or as they may be required by applicable law. The covenants for the notes require us to keep all of our insurable properties insured against loss or damage at least equal to their then full insurable value. We have an insurance policy that has no terrorism exclusion, except for non-certified nuclear, chemical and biological acts of terrorism. Our financial condition and results of operations are subject to the risks associated with acts of terrorism and the potential for uninsured losses as the result of any such acts. Effective November 26, 2002, under this existing coverage, any losses caused by certified acts of terrorism would be partially reimbursed by the United States under a formula established by federal law. Under this formula, the United States pays 85% of covered terrorism losses exceeding the statutorily established deductible paid by the insurance provider, and insurers pay 10% until aggregate insured losses from all insurers reach $100 billion in a calendar year. If the aggregate amount of insured losses under this program exceeds $100 billion during the applicable period for all insured and insurers combined, then each insurance provider will not be liable for payment of any amount which exceeds the aggregate amount of $100 billion . On January 12, 2015, the Terrorism Risk Insurance Program Reauthorization Act of 2015 was signed into law and extended the program through December 31, 2020. NOTES PAYABLE Our unsecured notes outstanding as of December 31, 2017 are as follows (in thousands): Coupon/Stated Rate Effective Rate (1) Principal Amount Maturity Date (2) 10 Year Unsecured Notes 4.95 % 5.05 % $ 250,000 10/1/2020 2015 Term Loan 1 Month LIBOR + 110 basis points 2.72 % 150,000 3/15/2021 10 Year Unsecured Notes 3.95 % 4.02 % 300,000 10/15/2022 2016 Term Loan 1 Month LIBOR + 165 basis points 2.86 % 150,000 7/21/2023 30 Year Unsecured Notes 7.25 % 7.36 % 50,000 2/25/2028 Total principal 900,000 Premiums and discounts, net (1,580 ) Deferred issuance costs, net (4,062 ) Total $ 894,358 (1) For fixed rate notes, the effective rate represents the yield on issuance date, including the effects of discounts on the notes. For variable rate notes, the effective rate represents the rate as fixed by interest rate derivatives (see note 7 ). (2) No principal amounts are due prior to maturity. During the third quarter of 2016, we entered into a seven year, $150.0 million unsecured term loan ("2016 Term Loan") maturing on July 21, 2023 with a deferred draw period of up to six months commencing on July 22, 2016 . The 2016 Term Loan bears interest at a rate of either LIBOR plus a margin ranging from 1.50% to 2.45% or the base rate plus a margin ranging from 0.5% to 1.45% (in each case depending upon Washington REIT’s credit rating). The base rate is the highest of the administrative agent's prime rate, the federal funds rate plus 0.50% and the daily one-month LIBOR rate plus 1.0% . The 2016 Term Loan bears interest at a rate of one month LIBOR plus 165 basis points, based on Washington REIT's current unsecured debt ratings. We borrowed $100.0 million on the term loan in the fourth quarter of 2016, and borrowed the remaining $50.0 million in January 2017. We also entered into forward interest rate derivatives commencing on March 31, 2017 to effectively fix the interest rate on the 2016 Term Loan at 2.86% (see note 7 ). The required principal payments as of December 31, 2017 are as follows (in thousands): 2018 $ — 2019 — 2020 250,000 2021 150,000 2022 300,000 Thereafter 200,000 $ 900,000 Interest on these notes is payable semi-annually, except for the term loans, for which interest is payable monthly. These notes contain certain financial and non-financial covenants, all of which we have met as of December 31, 2017 . Included in these covenants is the requirement to maintain a minimum level of unencumbered assets, as well as limits on our total indebtedness, secured indebtedness and required debt service payments.

Notes Payable

Notes Payable	12 Months Ended
	Dec. 31, 2017
Notes Payable [Abstract]
Notes Payable	UNSECURED LINES OF CREDIT PAYABLE During the second quarter of 2015, we terminated our $100.0 million unsecured line of credit maturing in June 2015 and our $400.0 million unsecured line of credit maturing in July 2016 , and executed a new $600.0 million unsecured credit agreement ("Revolving Credit Facility") that matures in June 2019 , unless extended pursuant to one or both of the two six -month extension options. The Revolving Credit Facility has an accordion feature that allows us to increase the facility to $1.0 billion , subject to the extent the lenders agree to provide additional revolving loan commitments or term loans. In September 2015, we entered into a $150.0 million unsecured term loan ("2015 Term Loan") by executing a portion of the accordion feature under the Revolving Credit Facility. The 2015 Term Loan has a 5.5 year term and currently has an interest rate of one month LIBOR plus 110 basis points, based on Washington REIT's current unsecured debt ratings. We entered into two interest rate swaps to effectively fix the interest rate at 2.7% (see note 7 ). The amount of the Revolving Credit Facility unused and available at December 31, 2017 was as follows (in thousands): Committed capacity $ 600,000 Borrowings outstanding (166,000 ) Unused and available $ 434,000 We executed borrowings and repayments on the Revolving Credit Facility during 2017 as follows (in thousands): Balance at December 31, 2016 $ 120,000 Borrowings 274,000 Repayments (228,000 ) Balance at December 31, 2017 $ 166,000 The Revolving Credit Facility bears interest at a rate of either LIBOR plus a margin ranging from 0.875% to 1.55% or the base rate plus a margin ranging from 0% to 0.55% (in each case depending upon Washington REIT’s credit rating). The base rate is the highest of the administrative agent's prime rate, the federal funds rate plus 0.5% and the LIBOR market index rate plus 1.0% . As of December 31, 2017 , the interest rate on the facility is LIBOR plus 1.0% and the one month LIBOR was 1.56% . All outstanding advances for the Revolving Credit Facility are due and payable upon maturity in June 2019 , unless extended pursuant to one or both of the two six-month extension options. Interest only payments are due and payable generally on a monthly basis. In addition, the Revolving Credit Facility requires the payment of a facility fee ranging from 0.125% to 0.30% (depending on Washington REIT’s credit rating) on the $600.0 million committed capacity, without regard to usage. As of December 31, 2017 , the facility fee is 0.20% . For the three years ended December 31, 2017 , we recognized interest expense (excluding facility fees) and facility fees as follows (in thousands): Year Ended December 31, 2017 2016 2015 Interest expense (excluding facility fees) $ 3,857 $ 3,272 $ 2,266 Facility fees 1,217 1,220 1,241 The Revolving Credit Facility contains certain financial and non-financial covenants, all of which we have met as of December 31, 2017 and 2016 . Included in these covenants are limits on our total indebtedness, secured and unsecured indebtedness and required debt service payments. Information related to revolving credit facilities for the three years ended December 31, 2017 as follows (in thousands, except percentage amounts): Year Ended December 31, 2017 2016 2015 Total revolving credit facilities at December 31 $ 600,000 $ 600,000 $ 600,000 Borrowings outstanding at December 31 166,000 120,000 105,000 Weighted average daily borrowings during the year 179,633 214,962 167,573 Maximum daily borrowings during the year 252,000 358,000 350,000 Weighted average interest rate during the year 2.15 % 1.52 % 1.35 % Weighted average interest rate on borrowings outstanding at December 31 2.54 % 1.64 % 1.36 % The covenants under our Revolving Credit Facility require us to insure our properties against loss or damage in amounts customarily maintained by similar businesses or as they may be required by applicable law. The covenants for the notes require us to keep all of our insurable properties insured against loss or damage at least equal to their then full insurable value. We have an insurance policy that has no terrorism exclusion, except for non-certified nuclear, chemical and biological acts of terrorism. Our financial condition and results of operations are subject to the risks associated with acts of terrorism and the potential for uninsured losses as the result of any such acts. Effective November 26, 2002, under this existing coverage, any losses caused by certified acts of terrorism would be partially reimbursed by the United States under a formula established by federal law. Under this formula, the United States pays 85% of covered terrorism losses exceeding the statutorily established deductible paid by the insurance provider, and insurers pay 10% until aggregate insured losses from all insurers reach $100 billion in a calendar year. If the aggregate amount of insured losses under this program exceeds $100 billion during the applicable period for all insured and insurers combined, then each insurance provider will not be liable for payment of any amount which exceeds the aggregate amount of $100 billion . On January 12, 2015, the Terrorism Risk Insurance Program Reauthorization Act of 2015 was signed into law and extended the program through December 31, 2020. NOTES PAYABLE Our unsecured notes outstanding as of December 31, 2017 are as follows (in thousands): Coupon/Stated Rate Effective Rate (1) Principal Amount Maturity Date (2) 10 Year Unsecured Notes 4.95 % 5.05 % $ 250,000 10/1/2020 2015 Term Loan 1 Month LIBOR + 110 basis points 2.72 % 150,000 3/15/2021 10 Year Unsecured Notes 3.95 % 4.02 % 300,000 10/15/2022 2016 Term Loan 1 Month LIBOR + 165 basis points 2.86 % 150,000 7/21/2023 30 Year Unsecured Notes 7.25 % 7.36 % 50,000 2/25/2028 Total principal 900,000 Premiums and discounts, net (1,580 ) Deferred issuance costs, net (4,062 ) Total $ 894,358 (1) For fixed rate notes, the effective rate represents the yield on issuance date, including the effects of discounts on the notes. For variable rate notes, the effective rate represents the rate as fixed by interest rate derivatives (see note 7 ). (2) No principal amounts are due prior to maturity. During the third quarter of 2016, we entered into a seven year, $150.0 million unsecured term loan ("2016 Term Loan") maturing on July 21, 2023 with a deferred draw period of up to six months commencing on July 22, 2016 . The 2016 Term Loan bears interest at a rate of either LIBOR plus a margin ranging from 1.50% to 2.45% or the base rate plus a margin ranging from 0.5% to 1.45% (in each case depending upon Washington REIT’s credit rating). The base rate is the highest of the administrative agent's prime rate, the federal funds rate plus 0.50% and the daily one-month LIBOR rate plus 1.0% . The 2016 Term Loan bears interest at a rate of one month LIBOR plus 165 basis points, based on Washington REIT's current unsecured debt ratings. We borrowed $100.0 million on the term loan in the fourth quarter of 2016, and borrowed the remaining $50.0 million in January 2017. We also entered into forward interest rate derivatives commencing on March 31, 2017 to effectively fix the interest rate on the 2016 Term Loan at 2.86% (see note 7 ). The required principal payments as of December 31, 2017 are as follows (in thousands): 2018 $ — 2019 — 2020 250,000 2021 150,000 2022 300,000 Thereafter 200,000 $ 900,000 Interest on these notes is payable semi-annually, except for the term loans, for which interest is payable monthly. These notes contain certain financial and non-financial covenants, all of which we have met as of December 31, 2017 . Included in these covenants is the requirement to maintain a minimum level of unencumbered assets, as well as limits on our total indebtedness, secured indebtedness and required debt service payments.

Derivative Instruments

Derivative Instruments	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments	DERIVATIVE INSTRUMENTS On September 15, 2015 , we entered into two interest rate swap arrangements with a total notional amount of $150.0 million to swap the floating interest rate under the 2015 Term Loan (see note 6 ) to an all-in fixed interest rate of 2.72% starting on October 15, 2015 and extending until the maturity of the 2015 Term Loan on March 15, 2021 . On July 22, 2016 , we entered into two forward interest rate swap arrangements with a total notional amount of $150.0 million to swap the floating interest rate under the 2016 Term Loan (see note 6) to an all-in fixed interest rate of 2.86% , starting on March 31, 2017 and extending until the maturity of the 2016 Term Loan on July 21, 2023 . The interest rate swaps qualify as cash flow hedges and are recorded at fair value in accordance with GAAP, based on discounted cash flow methodologies and observable inputs. We record the effective portion of changes in fair value of the cash flow hedges in other comprehensive income (loss). The resulting unrealized loss on the effective portions of the cash flow hedges was the only activity in other comprehensive income (loss) during the periods presented in our consolidated financial statements. We assess the effectiveness of our cash flow hedges both at inception and on an ongoing basis. The cash flow hedges were effective for 2017 and 2016 and hedge ineffectiveness did not impact earnings in 2017 and 2016 . The fair values of the interest rate swaps as of December 31, 2017 and 2016 , are as follows (in thousands): Aggregate Notional Amount Effective Date Fair Value Asset Derivatives December 31, Derivative Instrument Maturity Date 2017 2016 Interest rate swaps $ 150,000 October 15, 2015 March 15, 2021 $ 1,987 $ 417 Interest rate swaps 150,000 March 31, 2017 July 21, 2023 7,432 7,194 $ 300,000 $ 9,419 $ 7,611 We record interest rate swaps on our consolidated balance sheets with prepaid expenses and other assets when in a net asset position, and with accounts payable and other liabilities when in a net liability position. The interest rate swaps have been effective since inception. The gains or losses on the effective swaps are recognized in other comprehensive income (loss), as follows (in thousands): Year Ending December 31, 2017 2016 2015 Unrealized gain (loss) on interest rate hedges $ 1,808 $ 8,161 $ (550 ) Amounts reported in accumulated other comprehensive income (loss) related to derivatives will be reclassified to interest expense as interest payments are made on our variable-rate debt. During the next twelve months, we estimate that $1.1 million will be reclassified as a decrease to interest expense. We have agreements with each of our derivative counterparties that contain a provision whereby we could be declared in default on our derivative obligations if repayment of the underlying indebtedness is accelerated by the lender due to our default on the indebtedness. As of December 31, 2017 , the fair values of derivatives were in a net asset position of $9.4 million , including accrued interest but excluding any adjustment for nonperformance risk. As of December 31, 2017 , we have not posted any collateral related to these agreements. Derivative instruments expose us to credit risk in the event of non-performance by the counterparty under the terms of the interest rate hedge agreement. We believe that we minimize our credit risk on these transactions by dealing with major, creditworthy financial institutions. We monitor the credit ratings of counterparties and our exposure to any single entity, thus minimizing our credit risk concentration.

Fair Value Disclosures

Fair Value Disclosures	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Disclosures	FAIR VALUE DISCLOSURES Assets and Liabilities Measured at Fair Value For assets and liabilities measured at fair value on a recurring basis, quantitative disclosures about the fair value measurements are required to be disclosed separately for each major category of assets and liabilities, as follows: Level 1: Quoted prices in active markets for identical assets Level 2: Significant other observable inputs Level 3: Significant unobservable inputs The only assets or liabilities we had at December 31, 2017 and 2016 that are recorded at fair value on a recurring basis are the assets held in the Supplemental Executive Retirement Plan ("SERP"), which primarily consists of investments in mutual funds, and the interest rate swaps (see note 7 ). We base the valuations related to the SERP on assumptions derived from significant other observable inputs and accordingly these valuations fall into Level 2 in the fair value hierarchy. The valuation of the interest rate swaps is determined using widely accepted valuation techniques, including discounted cash flow analysis on the expected cash flows of each interest rate swap. This analysis reflects the contractual terms of the interest rate swaps, including the period to maturity, and uses observable market-based inputs, including interest rate curves and implied volatilities. The fair values of interest rate swaps are determined using the market standard methodology of netting the discounted future fixed cash payments (or receipts) and the discounted expected variable cash receipts (or payments). The variable cash payments (or receipts) are based on an expectation of future interest rates (forward curves) derived from observable market interest rate curves. To comply with the provisions of ASC 820, we incorporate credit valuation adjustments in the fair value measurements to appropriately reflect both our own nonperformance risk and the respective counterparty’s nonperformance risk. These credit valuation adjustments were concluded to not be significant inputs for the fair value calculations for the periods presented. In adjusting the fair value of our derivative contracts for the effect of nonperformance risk, we have considered the impact of netting and any applicable credit enhancements, such as the posting of collateral, thresholds, mutual puts and guarantees. The valuation of interest rate swaps fall into Level 2 in the fair value hierarchy. The fair values of these assets and liabilities at December 31, 2017 and 2016 were as follows (in thousands): December 31, 2017 December 31, 2016 Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: SERP $ 1,858 $ — $ 1,858 $ — $ 1,407 $ — $ 1,407 $ — Interest rate swaps 9,419 — 9,419 — 7,611 — 7,611 — Financial Assets and Liabilities Not Measured at Fair Value The following disclosures of estimated fair value were determined by management using available market information and established valuation methodologies, including discounted cash flow. Many of these estimates involve significant judgment. The estimated fair value disclosed may not necessarily be indicative of the amounts we could realize on disposition of the financial instruments. The use of different market assumptions or estimation methodologies could have an effect on the estimated fair value amounts. In addition, fair value estimates are made at a point in time and thus, estimates of fair value subsequent to December 31, 2017 may differ significantly from the amounts presented. Below is a summary of significant methodologies used in estimating fair values and a schedule of fair values at December 31, 2017 . Cash and Cash Equivalents and Restricted Cash Cash and cash equivalents and restricted cash include cash and commercial paper with original maturities of less than 90 days , which are valued at the carrying value, which approximates fair value due to the short maturity of these instruments (Level 1 inputs). Notes Receivable We acquired a note receivable ("2445 M Street note") in 2008 with the purchase of 2445 M Street. This note was repaid during the fourth quarter of 2017. Prior to its repayment, we estimated the fair value of the 2445 M Street note based on a discounted cash flow methodology using market discount rates (Level 3 inputs). Debt Mortgage notes payable consist of instruments in which certain of our real estate assets are used for collateral. We estimate the fair value of the mortgage notes payable by discounting the contractual cash flows at a rate equal to the relevant treasury rates (with respect to the timing of each cash flow) plus credit spreads estimated through independent comparisons to real estate assets or loans with similar characteristics. Lines of credit payable consist of bank facilities which we use for various purposes including working capital, acquisition funding and capital improvements. The lines of credit advances and term loans with floating interest rates are priced at a specified rate plus a spread. We estimate the market value based on a comparison of the spreads of the advances to market given the adjustable base rate. We estimate the fair value of the notes payable by discounting the contractual cash flows at a rate equal to the relevant treasury rates (with respect to the timing of each cash flow) plus credit spreads derived using the relevant securities’ market prices. We classify these fair value measurements as Level 3 as we use significant unobservable inputs and management judgment due to the absence of quoted market prices. As of December 31, 2017 and 2016 , the carrying values and estimated fair values of our financial instruments were as follows (in thousands): December 31, 2017 2016 Carrying Value Fair Value Carrying Value Fair Value Cash and cash equivalents $ 9,847 $ 9,847 $ 11,305 $ 11,305 Restricted cash 2,776 2,776 6,317 6,317 2445 M Street note receivable — — 2,089 2,173 Mortgage notes payable 95,141 97,181 148,540 149,997 Lines of credit payable 166,000 166,000 120,000 120,000 Notes payable 894,358 931,377 843,084 873,516

Stock Based Compensation

Stock Based Compensation	12 Months Ended
	Dec. 31, 2017
Share-based Compensation [Abstract]
Stock Based Compensation	STOCK BASED COMPENSATION Washington REIT maintains short-term and long-term incentive plans that allow for stock-based awards to officers and non-officer employees. Stock based awards are provided to officers and non-officer employees, as well as trustees, under the Washington Real Estate Investment Trust 2016 Omnibus Incentive Plan which allows for awards in the form of restricted shares, restricted share units, options, and other awards up to an aggregate of 2,400,000 shares over the ten year period in which the plan will be in effect. Restricted share units are converted into shares of our stock upon full vesting through the issuance of new shares. There were no options issued or outstanding as of December 31, 2017 and 2016 . Short-Term Incentive Plan ("STIP") Under the STIP, executive officers earn awards, payable 50% in cash and 50% in restricted shares, based on a percentage of salary and an achievement rating subject to the discretion of the Compensation Committee of the board of trustees in consideration of various performance conditions and other subjective factors during a one -year performance period. With respect to the 50% of the STIP award payable in restricted shares, the restricted shares will vest over a three -year period commencing on the January 1 following the end of the one -year performance period. Prior to the adoption of the 2016 Omnibus Incentive Plan, stock based awards to officers, non-officer employees and trustees were issued under the Washington Real Estate Investment Trust 2007 Omnibus Long-Term Incentive Plan which allowed for awards in the form of restricted shares, restricted share units, options and other awards up to an aggregate of 2,000,000 shares while the plan was in effect. The grant date for the 50% of the STIP award payable in restricted shares is the date on which the Compensation Committee approves the STIP awards. We recognize compensation expense on this 50% when the grant date occurs at the end of the one -year period through the three -year vesting period. Bonuses payable under the short-term incentive plans for non-executive officers and staff are payable 100% in cash. Long-Term Incentive Plan ("LTIP") Under the LTIP, executive officers earn awards payable, 75% in unrestricted shares and 25% in restricted shares, based on a percentage of salary and the achievement of certain market conditions. LTIP performance is evaluated based 50% on absolute total shareholder return (“TSR”) and 50% on relative TSR over a three -year evaluation period with a new three -year period initiating under the existing plan each year. The officers' total award opportunities under the LTIP stated as a percentage of base salary ranges from 80% to 150% at target level. The unrestricted shares vest immediately at the end of the three -year performance period, and the restricted shares vest over a one -year period commencing on the January 1 following the end of the three -year performance period. In addition, during the transition period from the prior LTIP in 2014, the board of trustees awarded similar transition awards with defined performance periods of one and two years and modified vesting to account for the transition. We recognize compensation expense ratably (over three years for the 75% unrestricted shares and over four years for the 25% restricted shares) based on the grant date fair value, as determined using a Monte Carlo simulation, and regardless of whether the market conditions are achieved and the awards ultimately vest. We use a binomial model which employs the Monte Carlo method as of the grant date to determine the fair value of the officer LTIP awards. The market condition performance measurement is based on total shareholder return on both an absolute basis ( 50% weighting) and relative to a defined population of peer companies ( 50% weighting). The model evaluates the awards for changing total shareholder return over the term of the vesting, on an absolute basis and relative to the peer companies, and uses random simulations that are based on past stock characteristics as well as dividend growth and other factors for Washington REIT and each of the peer companies. The assumptions used to value the officer LTIP awards were as follows: 2017 Awards 2016 Awards 2015 Awards Expected volatility (1) 18.5% - 18.7% 18.2 % 17.2% - 17.5% Risk-free interest rate (2) 1.5 % 1.3 % 1.0% - 1.1% Expected term (3) 3 and 4 years 3 and 4 years 3 and 4 years Share price at grant date $30.84 - $32.69 $27.06 $27.66 - $27.76 (1) Expected volatility based upon historical volatility of our daily closing share price. (2) Risk-free interest rate based on U.S. treasury constant maturity bonds on the measurement date with a maturity equal to the market condition performance period. (3) Expected term based on the market condition performance period. The calculated grant date fair value as a percentage of base salary for the officers for the three-year performance period that commenced in 2017 ranged from approximately 37% to 67% for the 50% of the LTIP based on relative TSR and from 13% to 31% for the 50% of the LTIP based on absolute TSR. The calculated grant date fair value as a percentage of base salary for the officers for the three-year performance period that commenced in 2016 ranged from approximately 38% to 66% for the 50% of the LTIP based on relative TSR and from 17% to 30% for the 50% of the LTIP based on absolute TSR. The calculated grant date fair value as a percentage of base salary for the officers for the three-year performance period that commenced in 2015 ranged from approximately 40% to 69% for the 50% of the LTIP based on relative TSR and from 13% to 29% for the 50% of the LTIP based on absolute TSR. During 2017, our chief executive officer was granted a one-time equity award of 100,000 restricted shares. None of the restricted shares vest until the fifth anniversary of the grant date, at which time 100% of the restricted shares will vest, subject to Mr. McDermott's continued employment with Washington REIT until such vesting date. Our non-executive officers and other employees earn restricted share unit awards under a long-term incentive plan for non-executive officers and staff, which became effective on January 1, 2016, based upon various percentages of their salaries and annual performance calculations. The restricted share unit awards vest ratably over three years from December 15 preceding the grant date based upon continued employment. For awards made through 2016, the service inception date precedes the grant date. For these awards, we initially measured compensation expense for awards with performance conditions at fair value at the service inception date based on probability of payout, and we remeasured compensation expense at subsequent reporting dates until all of the award's key terms and conditions are known and the grant date is established. We recognized compensation expense for these awards according to a graded vesting schedule over the four -year requisite service period. During 2016, we amended the LTIP for other officers and other employees. Among the changes to the LTIP was the inclusion of strategic goals with subjective performance criteria. As a result of these changes, the service inception date is the same as the grant date for awards made under the amended LTIP. We recognize compensation expense for these awards according to a graded vesting schedule over the three-year requisite service period. Restricted share awards made to retirement-eligible employees fully vest on the grant date. Employees are considered retirement-eligible when they are both over the age of 55 and have been employed by Washington REIT for at least 20 years, or over the age of 65. We fully recognize compensation expense for such awards as of the grant date. Trustee Awards We award share based compensation to our trustees in the form of restricted shares which vest immediately and are restricted from sale for the period of the trustees' service. The value of share-based compensation for each trustee was $100,000 for each of three years ended December 31, 2017 . Total Compensation Expense Total compensation expense recognized in the consolidated financial statements for each of the three years ended December 31, 2017 for all share based awards was $4.8 million , $3.5 million and $5.1 million , respectively, net of capitalized stock-based compensation expense of $0.2 million , $0.1 million and $0.6 million , respectively. Restricted Share Awards with Performance and Service Conditions The activity for the three years ended December 31, 2017 related to our restricted share awards, excluding those subject to market conditions, was as follows: Shares Wtd Avg Grant Fair Value Unvested at December 31, 2014 93,667 $ 25.22 Granted 251,642 27.80 Vested during year (212,856 ) 27.18 Forfeited (26,309 ) 26.77 Unvested at December 31, 2015 106,144 27.71 Granted 251,694 26.01 Vested during year (211,771 ) 29.21 Forfeited (38,368 ) 26.14 Unvested at December 31, 2016 107,699 26.47 Granted 330,639 32.46 Vested during year (194,569 ) 30.50 Forfeited (7,075 ) 27.43 Unvested at December 31, 2017 236,694 27.96 The total fair value of share grants vested for each of the three years ended December 31, 2017 was $5.9 million , $6.2 million and $5.8 million , respectively. As of December 31, 2017 , the total compensation cost related to non-vested share awards not yet recognized was $6.6 million , which we expect to recognize over a weighted average period of 35 months . Restricted and Unrestricted Shares with Market Conditions Stock based awards with market conditions under the LTIP were granted in 2017, 2016 and 2015 with fair market values, as determined using a Monte Carlo simulation, as follows (in thousands): Grant Date Fair Value 2017 Awards 2016 Awards 2015 Awards Restricted Unrestricted Restricted Unrestricted Restricted Unrestricted Relative TSR $ 222 $ 666 $ 182 $ 546 $ 191 $ 634 Absolute TSR 100 299 82 246 76 254 The unamortized value of these awards with market conditions as of December 31, 2017 was as follows (in thousands): 2017 Awards 2016 Awards 2015 Awards Restricted Unrestricted Restricted Unrestricted Restricted Unrestricted Relative TSR $ 166 $ 444 $ 117 $ 314 $ 83 $ 165 Absolute TSR 75 199 53 142 33 66

Other Benefit Plans

Other Benefit Plans	12 Months Ended
	Dec. 31, 2017
Defined Benefit Plan [Abstract]
Other Benefit Plans	OTHER BENEFIT PLANS We have a Retirement Savings Plan (the “401(k) Plan”), which permits all eligible employees to defer a portion of their compensation in accordance with the Code. Under the 401(k) Plan, we may make discretionary contributions on behalf of eligible employees. For each of the three years ended December 31, 2017 , we made contributions to the 401(k) plan of $0.4 million , $0.4 million and $0.5 million , respectively. We have adopted non-qualified deferred compensation plans for the officers and members of the board of trustees. The plans allow for a deferral of a percentage of annual cash compensation and trustee fees. The plans are unfunded and payments are to be made out of the general assets of Washington REIT. The deferred compensation liability was $1.0 million and $0.9 million at December 31, 2017 and 2016 , respectively. In November 2005, the board of trustees approved the establishment of a SERP for the benefit of officers. This is a defined contribution plan under which, upon a participant's termination of employment from Washington REIT for any reason other than discharge for cause, the participant will be entitled to receive a benefit equal to the participant's accrued benefit times the participant's vested interest. We account for this plan in accordance with ASC 710-10 and ASC 320-10, whereby the investments are reported at fair value, and unrealized holding gains and losses are included in earnings. At December 31, 2017 and 2016 , the accrued benefit liability was $1.8 million and $1.3 million , respectively. For each of the three years ended December 31, 2017 , we recognized current service cost of $0.3 million , $0.2 million and $0.3 million , respectively.

Earnings Per Common Share

Earnings Per Common Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings per Common Share	EARNINGS PER COMMON SHARE We determine “Basic earnings per share” using the two-class method as our unvested restricted share awards and units have non-forfeitable rights to dividends, and are therefore considered participating securities. We compute basic earnings per share by dividing net income attributable to the controlling interest less the allocation of undistributed earnings to unvested restricted share awards and units by the weighted-average number of common shares outstanding for the period. We also determine “Diluted earnings per share” as the more dilutive of the two-class method or the treasury stock method with respect to the unvested restricted share awards. We further evaluate any other potentially dilutive securities at the end of the period and adjust the basic earnings per share calculation for the impact of those securities that are dilutive. Our dilutive earnings per share calculation includes the dilutive impact of operating partnership units under the if-converted method and our share based awards with performance conditions prior to the grant date and all market condition awards under the contingently issuable method. The computation of basic and diluted earnings per share for the three years ended December 31, 2017 was as follows (in thousands; except per share data): Year Ended December 31, 2017 2016 2015 Numerator: Net income $ 19,612 $ 119,288 $ 89,187 Net loss attributable to noncontrolling interests 56 51 553 Allocation of undistributed earnings to unvested restricted share awards and units to continuing operations (362 ) (310 ) (269 ) Adjusted net income attributable to the controlling interests $ 19,306 $ 119,029 $ 89,471 Denominator: Weighted average shares outstanding – basic 76,820 72,163 68,177 Effect of dilutive securities: Operating partnership units 9 — — Employee stock options and restricted share awards 106 176 133 Weighted average shares outstanding – diluted 76,935 72,339 68,310 Basic net income attributable to the controlling interests per common share $ 0.25 $ 1.65 $ 1.31 Diluted net income attributable to the controlling interests per common share $ 0.25 $ 1.65 $ 1.31 Dividends declared per common share $ 1.20 $ 1.20 $ 1.20

Rentals Under Operating Leases

Rentals Under Operating Leases	12 Months Ended
	Dec. 31, 2017
Leases, Operating [Abstract]
Rentals Under Operating Leases	RENTALS UNDER OPERATING LEASES As of December 31, 2017 , non-cancelable commercial operating leases provide for minimum rental income were as follows (in thousands): 2018 $ 190,391 2019 172,289 2020 157,694 2021 132,150 2022 109,713 Thereafter 376,904 $ 1,139,141 Apartment leases are not included as the terms are generally for one year. Most of these commercial leases increase in future years based on agreed-upon percentages or in some instances, changes in the Consumer Price Index. Real estate tax, operating expense and common area maintenance reimbursement income from continuing operations for the three years ended December 31, 2017 was $35.4 million , $35.2 million and $34.6 million , respectively.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES Development Commitments At December 31, 2017 , we had no committed contracts outstanding with third parties in connection with our development and redevelopment projects. Litigation We are involved from time to time in various legal proceedings, lawsuits, examinations by various tax authorities and claims that have arisen in the ordinary course of business. Management believes that the resolution of any such current matters will not have a material adverse effect on our financial condition or results of operations.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2017
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Segment Information	SEGMENT INFORMATION We evaluate real estate performance and allocate resources by property type and have three reportable segments: office, multifamily, and retail. Office properties provide office space for various types of businesses and professions. Multifamily properties provide rental housing for individuals and families throughout the Washington metro region. Retail properties are typically grocery store anchored neighborhood centers that include other small shop tenants or regional power centers with several junior box tenants. Real estate rental revenue as a percentage of the total for each of the reportable operating segments in continuing operations for the three years ended December 31, 2017 was as follows: Year Ended December 31, 2017 2016 2015 Office 52 % 53 % 57 % Multifamily 29 % 27 % 22 % Retail 19 % 20 % 21 % The percentage of income producing real estate assets classified as held and used, at cost, for each of the reportable operating segments in continuing operations as of December 31, 2017 and 2016 was as follows: December 31, 2017 2016 Office 50 % 50 % Multifamily 33 % 33 % Retail 17 % 17 % The accounting policies of each of the segments are the same as those described in note 2. We evaluate performance based upon net operating income from the combined properties in each segment. Our reportable operating segments are consolidations of similar properties. GAAP requires that segment disclosures present the measure(s) used by the chief operating decision maker for purposes of assessing segments’ performance. Net operating income is a key measurement of our segment profit and loss. Net operating income is defined as segment real estate rental revenue less segment real estate expenses. The following tables present revenues, net operating income, capital expenditures and total assets for the three years ended December 31, 2017 from these segments, and reconciles net operating income of reportable segments to net income attributable to the controlling interests as reported (in thousands): Year Ended December 31, 2017 Office Retail Multifamily Corporate Consolidated Real estate rental revenue $ 167,438 $ 62,390 $ 95,250 $ — $ 325,078 Real estate expenses 62,824 15,186 37,640 — 115,650 Net operating income $ 104,614 $ 47,204 $ 57,610 $ — $ 209,428 Depreciation and amortization (112,056 ) General and administrative (22,580 ) Interest expense (47,534 ) Other income 507 Gain on sale of real estate 24,915 Real estate impairment (33,152 ) Income tax benefit 84 Net income 19,612 Less: Net loss attributable to noncontrolling interests 56 Net income attributable to the controlling interests $ 19,668 Capital expenditures $ 30,407 $ 2,128 $ 27,980 $ 3,866 $ 64,381 Total assets $ 1,203,187 $ 346,580 $ 767,279 $ 42,380 $ 2,359,426 Year Ended December 31, 2016 Office Retail Multifamily Corporate and Other Consolidated Real estate rental revenue $ 165,934 $ 61,566 $ 85,764 $ — $ 313,264 Real estate expenses 64,405 15,860 34,748 — 115,013 Net operating income $ 101,529 $ 45,706 $ 51,016 $ — $ 198,251 Depreciation and amortization (108,406 ) General and administrative (19,545 ) Casualty gain 676 Acquisition costs (1,178 ) Interest expense (53,126 ) Other income 297 Gain on sale of real estate 101,704 Income tax benefit 615 Net income 119,288 Less: Net loss attributable to noncontrolling interests 51 Net income attributable to the controlling interests $ 119,339 Capital expenditures $ 30,337 $ 8,821 $ 17,936 $ 920 $ 58,014 Total assets $ 1,104,589 $ 352,056 $ 762,695 $ 34,279 $ 2,253,619 Year Ended December 31, 2015 Office Retail Multifamily Corporate Consolidated Real estate rental revenue $ 174,378 $ 63,507 $ 68,542 $ — $ 306,427 Real estate expenses 67,228 15,606 29,400 — 112,234 Net operating income $ 107,150 $ 47,901 $ 39,142 $ — $ 194,193 Depreciation and amortization (108,935 ) General and administrative (20,123 ) Real estate impairment (5,909 ) Acquisition costs (2,056 ) Interest expense (59,546 ) Other income 709 Loss on extinguishment of debt (119 ) Gain on sale of real estate 91,107 Income tax expense (134 ) Net income 89,187 Less: Net loss attributable to noncontrolling interests 553 Net income attributable to the controlling interests $ 89,740 Capital expenditures $ 29,745 $ 3,897 $ 7,865 $ 2,129 $ 43,636 Total assets $ 1,265,570 $ 354,123 $ 529,773 $ 41,702 $ 2,191,168

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) Unaudited financial data by quarter in each of the years ended December 31, 2017 and 2016 were as follows (in thousands, except for per share data): Quarter (1), (2) First Second Third Fourth 2017 Real estate rental revenue $ 77,501 $ 83,456 $ 82,819 $ 81,302 Net income $ 6,615 $ 7,847 $ 2,813 $ 2,337 Net income attributable to the controlling interests $ 6,634 $ 7,864 $ 2,833 $ 2,337 Net income per share Basic $ 0.09 $ 0.10 $ 0.04 $ 0.03 Diluted $ 0.09 $ 0.10 $ 0.04 $ 0.03 2016 Real estate rental revenue $ 77,137 $ 79,405 $ 79,770 $ 76,952 Net income $ 2,379 $ 31,821 $ 79,662 $ 5,426 Net income attributable to the controlling interests $ 2,384 $ 31,836 $ 79,674 $ 5,445 Net income per share Basic $ 0.03 $ 0.44 $ 1.07 $ 0.07 Diluted $ 0.03 $ 0.44 $ 1.07 $ 0.07 (1) With regard to per share calculations, the sum of the quarterly results may not equal full year results due to rounding. (2) The fourth quarter of 2017 includes gain on sale of real estate classified as continuing operations of $24.9 million . The second and third quarters of 2016 include gains on sale of real estate classified as continuing operations of $24.1 million and $77.6 million , respectively. The third and fourth quarters of 2017 include real estate impairments of $5.0 million and $28.2 million , respectively.

Shareholders' Equity

Shareholders' Equity	12 Months Ended
	Dec. 31, 2017
Stockholders' Equity Note [Abstract]
Shareholders' Equity	SHAREHOLDERS' EQUITY During the second quarter of 2016, we issued approximately 5.3 million common shares, including 0.7 million shares issued pursuant to the underwriters' over-allotment option, at a price to the public of $28.20 per share. We received net proceeds of approximately $143.4 million . During the second quarter of 2015, we entered into four separate equity distribution agreements (collectively, the “Equity Distribution Agreements”) with each of Wells Fargo Securities, LLC, BNY Mellon Capital Markets, LLC, Citigroup Global Markets Inc. and RBC Capital Markets, LLC relating to the issuance and sale of up to $200.0 million of our common shares from time to time. Sales of our common shares are made at market prices prevailing at the time of sale. We use net proceeds from the sale of common shares under this program for general corporate purposes, including, without limitation, working capital, the acquisition, renovation, expansion, improvement, development or redevelopment of income producing properties or the repayment of debt. During 2017 and 2016, we issued 3.6 million and 0.9 million common shares, respectively, under the Equity Distribution Agreements at a weighted average price of $32.06 and $33.32 per share, respectively, raising $113.2 million and $29.6 million in net proceeds, respectively. The Equity Distribution Agreements replace Washington REIT's prior sales agency financing agreement with BNY Mellon Capital Markets, LLC, which expired by its terms in June 2015. During 2015, Washington REIT issued 0.2 million common shares at a weighted average price of $28.34 , for net proceeds of $5.2 million . We have a dividend reinvestment program, whereby shareholders may use their dividends and optional cash payments to purchase common shares. The common shares sold under this program may either be common shares issued by us or common shares purchased in the open market. Net proceeds under this program are used for general corporate purposes. During the 2017 and 2016, we issued approximately 80,000 and 23,000 common shares, respectively, under this program at a weighted average price of $32.25 and $30.98 per share, respectively, for net proceeds of $2.6 million and $0.7 million , respectively.

Deferred Costs

Deferred Costs	12 Months Ended
	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deferred Costs	DEFERRED COSTS As of December 31, 2017 and 2016 , deferred leasing costs and deferred leasing incentives were included in prepaid expenses and other assets as follows (in thousands): December 31, 2017 2016 Gross Carrying Value Accumulated Amortization Net Gross Carrying Value Accumulated Amortization Net Deferred leasing costs $ 68,213 $ 28,523 $ 39,690 $ 58,391 $ 22,748 $ 35,643 Deferred leasing incentives 24,946 11,114 13,832 21,157 8,061 13,096 Amortization, including write-offs, of deferred leasing costs and deferred leasing incentives from continuing operations for the three years ended December 31, 2017 were as follows (in thousands): Year Ended December 31, 2017 2016 2015 Deferred leasing costs amortization $ 6,418 $ 6,076 $ 5,983 Deferred leasing incentives amortization 3,163 2,994 2,848

Subsequent Event

Subsequent Event	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Event	SUBSEQUENT EVENT On January 18, 2018, we closed on the purchase of Arlington Tower, a 398,000 square foot office building in Arlington, Virginia for a contract purchase price of $250.0 million . We funded the acquisition with borrowings on our Revolving Credit Facility and proceeds from the sale of Braddock Metro Center (see note 3).

Schedule II

Schedule II	12 Months Ended
	Dec. 31, 2017
Valuation and Qualifying Accounts [Abstract]
Schedule II	SCHEDULE II VALUATION AND QUALIFYING ACCOUNTS FOR THE YEARS ENDED DECEMBER 31, 2017 , 2016 AND 2015 (IN THOUSANDS) Balance at Beginning of Year Additions Charged to Expenses Net Deductions (Recoveries) Balance at End of Year Allowance for doubtful accounts 2017 $ 2,377 $ 882 $ (833 ) $ 2,426 2016 $ 2,297 $ 1,706 $ (1,626 ) $ 2,377 2015 $ 3,392 $ 1,368 $ (2,463 ) $ 2,297 Valuation allowance for deferred tax assets 2017 $ 2,882 $ — $ (1,469 ) $ 1,413 2016 $ 5,705 $ — $ (2,823 ) $ 2,882 2015 $ 5,714 $ — $ (9 ) $ 5,705

Schedule III

Schedule III	12 Months Ended
	Dec. 31, 2017
SEC Schedule III, Real Estate and Accumulated Depreciation Disclosure [Abstract]
Schedule III	SCHEDULE III Initial Cost (b) Net Improvements (Retirement) since Acquisition Gross Amounts at Which Carried at December 31, 2017 Accumulated Depreciation at December 31, 2017 Properties Location Land Buildings and Improvements Land Buildings and Improvements Total (c) Year of Construction Date of Acquisition Net Rentable Square Feet Units Depreciation Life (d) Multifamily Properties 3801 Connecticut Avenue Washington, DC $ 420,000 $ 2,678,000 $ 16,263,000 $ 420,000 $ 18,941,000 $ 19,361,000 $ 11,526,000 1951 Jan 1963 178,000 307 30 years Roosevelt Towers Virginia 336,000 1,996,000 12,890,000 336,000 14,886,000 15,222,000 10,151,000 1964 May 1965 170,000 191 40 years Park Adams Virginia 287,000 1,654,000 12,935,000 287,000 14,589,000 14,876,000 9,968,000 1959 Jan 1969 173,000 200 35 years The Ashby at McLean (f) Virginia 4,356,000 17,102,000 23,569,000 4,356,000 40,671,000 45,027,000 25,312,000 1982 Aug 1996 274,000 256 30 years Bethesda Hill Apartments Maryland 3,900,000 13,412,000 13,896,000 3,900,000 27,308,000 31,208,000 18,904,000 1986 Nov 1997 225,000 195 30 years Bennett Park Virginia 2,861,000 917,000 80,278,000 4,774,000 79,282,000 84,056,000 34,586,000 2007 Feb 2001 215,000 224 28 years The Clayborne Virginia 269,000 — 31,041,000 699,000 30,611,000 31,310,000 15,050,000 2008 Jun 2003 60,000 74 26 years The Kenmore (a) Washington, DC 28,222,000 33,955,000 13,694,000 28,222,000 47,649,000 75,871,000 13,973,000 1948 Sep 2008 268,000 374 30 years The Maxwell Virginia 12,787,000 — 38,035,000 12,851,000 37,971,000 50,822,000 6,811,000 2014 Jun 2011 116,000 163 30 years The Paramount Virginia 8,568,000 38,716,000 2,345,000 8,568,000 41,061,000 49,629,000 7,715,000 1984 Oct 2013 141,000 135 30 years Yale West (a) Washington, DC 14,684,000 62,069,000 786,000 14,684,000 62,855,000 77,539,000 8,808,000 2011 Feb 2014 173,000 216 30 years The Wellington Virginia 30,548,000 116,563,000 10,161,000 30,548,000 126,724,000 157,272,000 11,206,000 1960 Jul 2015 600,000 711 30 years Wellington Land Parcel (Trove) (e) Virginia 15,000,000 — 14,690,000 — 29,690,000 29,690,000 — n/a Jul 2015 — n/a n/a Riverside Apartments Virginia 38,924,000 184,854,000 20,544,000 38,924,000 205,398,000 244,322,000 11,872,000 1971 May 2016 1,001,000 1,222 30 years Riverside Apartments Land Parcel (e) Virginia 15,968,000 — 3,254,000 — 19,222,000 19,222,000 — n/a May 2016 — n/a n/a $ 177,130,000 $ 473,916,000 $ 294,381,000 $ 148,569,000 $ 796,858,000 $ 945,427,000 $ 185,882,000 3,594,000 4,268 Office Buildings 1901 Pennsylvania Avenue Washington, DC $ 892,000 $ 3,481,000 $ 19,565,000 $ 892,000 $ 23,046,000 $ 23,938,000 $ 17,042,000 1960 May 1977 100,000 28 years 515 King Street Virginia 4,102,000 3,931,000 8,158,000 4,102,000 12,089,000 16,191,000 6,255,000 1966 Jul 1992 75,000 50 years 1220 19th Street Washington, DC 7,803,000 11,366,000 16,550,000 7,803,000 27,916,000 35,719,000 16,773,000 1976 Nov 1995 105,000 30 years 1600 Wilson Boulevard Virginia 6,661,000 16,742,000 28,677,000 6,661,000 45,419,000 52,080,000 25,295,000 1973 Oct 1997 170,000 30 years Silverline Center Virginia 12,049,000 71,825,000 100,170,000 12,049,000 171,995,000 184,044,000 86,729,000 1972 Nov 1997 549,000 30 years Courthouse Square Virginia — 17,096,000 9,448,000 — 26,544,000 26,544,000 15,441,000 1979 Oct 2000 118,000 30 years 1776 G Street Washington, DC 31,500,000 54,327,000 9,309,000 31,500,000 63,636,000 95,136,000 32,083,000 1979 Aug 2003 264,000 30 years Monument II Virginia 10,244,000 65,205,000 9,778,000 10,244,000 74,983,000 85,227,000 28,830,000 2000 Mar 2007 208,000 30 years 2000 M Street Washington, DC — 61,101,000 22,375,000 — 83,476,000 83,476,000 31,355,000 1971 Dec 2007 233,000 30 years 2445 M Street Washington, DC 46,887,000 106,743,000 (49,374,000 ) 37,333,000 66,923,000 104,256,000 9,099,000 1986 Dec 2008 292,000 30 years 925 Corporate Drive Virginia 4,518,000 24,801,000 1,333,000 4,518,000 26,134,000 30,652,000 9,747,000 2007 Jun 2010 135,000 30 years 1000 Corporate Drive Virginia 4,897,000 25,376,000 (186,000 ) 4,898,000 25,189,000 30,087,000 8,978,000 2009 Jun 2010 136,000 30 years 1140 Connecticut Avenue Washington, DC 25,226,000 50,495,000 15,987,000 25,226,000 66,482,000 91,708,000 18,774,000 1966 Jan 2011 184,000 30 years 1227 25th Street Washington, DC 17,505,000 21,319,000 8,653,000 17,505,000 29,972,000 47,477,000 8,391,000 1988 Mar 2011 137,000 30 years Braddock Metro Center Virginia 18,817,000 71,250,000 (14,808,000 ) 16,615,000 58,644,000 75,259,000 6,725,000 1985 Sep 2011 356,000 30 years John Marshall II Virginia 13,490,000 53,024,000 6,351,000 13,490,000 59,375,000 72,865,000 13,754,000 1996 Sep 2011 223,000 30 years Fairgate at Ballston Virginia 17,750,000 29,885,000 5,794,000 17,750,000 35,679,000 53,429,000 9,075,000 1988 Jun 2012 146,000 30 years Army Navy Building Washington, DC 30,796,000 39,315,000 10,642,000 30,796,000 49,957,000 80,753,000 7,583,000 1912 Mar 2014 109,000 30 years 1775 Eye Street, NW Washington, DC 48,086,000 51,074,000 8,473,000 48,086,000 59,547,000 107,633,000 10,842,000 1964 May 2014 188,000 30 years Watergate 600 Washington, DC 45,981,000 78,325,000 10,192,000 45,981,000 88,517,000 134,498,000 3,384,000 1972 Apr 2017 293,000 30 years $ 347,204,000 $ 856,681,000 $ 227,087,000 $ 335,449,000 $ 1,095,523,000 $ 1,430,972,000 $ 366,155,000 4,021,000 Initial Cost (b) Net Improvements (Retirement) since Acquisition Gross Amounts at Which Carried at December 31, 2017 Accumulated Depreciation at December 31, 2017 Properties Location Land Buildings and Improvements Land Buildings and Improvements Total (c) Year of Construction Date of Acquisition Net Rentable Square Feet Units Depreciation Life (d) Retail Centers Takoma Park Maryland $ 415,000 $ 1,084,000 $ 245,000 $ 366,000 $ 1,378,000 $ 1,744,000 $ 1,198,000 1962 Jul 1963 51,000 50 years Westminster Maryland 519,000 1,775,000 9,899,000 519,000 11,674,000 12,193,000 7,948,000 1969 Sep 1972 150,000 37 years Concord Centre Virginia 413,000 850,000 5,936,000 413,000 6,786,000 7,199,000 3,619,000 1960 Dec 1973 75,000 33 years Wheaton Park Maryland 796,000 857,000 4,853,000 796,000 5,710,000 6,506,000 4,114,000 1967 Sep 1977 74,000 50 years Bradlee Shopping Center Virginia 4,152,000 5,383,000 14,348,000 4,152,000 19,731,000 23,883,000 12,571,000 1955 Dec 1984 172,000 40 years Chevy Chase Metro Plaza Washington, DC 1,549,000 4,304,000 8,298,000 1,549,000 12,602,000 14,151,000 7,366,000 1975 Sep 1985 49,000 50 years Shoppes of Foxchase Virginia 5,838,000 2,979,000 14,812,000 5,838,000 17,791,000 23,629,000 7,914,000 1960 Jun 1994 134,000 50 years Frederick County Square Maryland 6,561,000 6,830,000 5,376,000 6,561,000 12,206,000 18,767,000 8,302,000 1973 Aug 1995 228,000 30 years 800 S. Washington Street Virginia 2,904,000 5,489,000 5,954,000 2,904,000 11,443,000 14,347,000 5,485,000 1951 Jun 1998 46,000 30 years Centre at Hagerstown Maryland 13,029,000 25,415,000 2,144,000 13,029,000 27,559,000 40,588,000 14,358,000 2000 Jun 2002 333,000 30 years Frederick Crossing Maryland 12,759,000 35,477,000 2,070,000 12,759,000 37,547,000 50,306,000 16,709,000 1999 Mar 2005 295,000 30 years Randolph Shopping Center Maryland 4,928,000 13,025,000 1,188,000 4,928,000 14,213,000 19,141,000 5,809,000 1972 May 2006 83,000 30 years Montrose Shopping Center Maryland 11,612,000 22,410,000 2,285,000 11,020,000 25,287,000 36,307,000 10,105,000 1970 May 2006 147,000 30 years Gateway Overlook Maryland 28,816,000 52,249,000 763,000 29,110,000 52,718,000 81,828,000 18,937,000 2007 Dec 2010 220,000 30 years Olney Village Center (a) Maryland 15,842,000 39,133,000 2,114,000 15,842,000 41,247,000 57,089,000 9,768,000 1979 Aug 2011 198,000 30 years Spring Valley Village (f) Washington, DC 10,836,000 32,238,000 4,532,000 10,836,000 36,770,000 47,606,000 4,177,000 1941 Oct 2014 78,000 30 years $ 120,969,000 $ 249,498,000 $ 84,817,000 $ 120,622,000 $ 334,662,000 $ 455,284,000 $ 138,380,000 2,333,000 Total $ 645,303,000 $ 1,580,095,000 $ 606,285,000 $ 604,640,000 $ 2,227,043,000 $ 2,831,683,000 $ 690,417,000 9,948,000 4,268 a) At December 31, 2017 , our properties were encumbered by non-recourse mortgage amounts as follows: $32.2 million on The Kenmore, $13.1 million on Olney Village Center and $46.6 million on Yale West. Mortgage amounts exclude premiums and debt loan costs. b) The purchase cost of real estate investments has been divided between land and buildings and improvements on the basis of management’s determination of the fair values. c) At December 31, 2017 , total land, buildings and improvements are carried at $1,983.3 million for federal income tax purposes. d) The useful life shown is for the main structure. Buildings and improvements are depreciated over various useful lives ranging from 3 to 50 years. e) As of December 31, 2017 , Washington REIT had under development multifamily properties, the Wellington land parcel (Trove) and Riverside Apartments land parcel. The value not yet placed into service at December 31, 2017 was $29.7 million and $19.2 million , respectively. f) As of December 31, 2017 , Washington REIT had investments in various development, redevelopment and renovation projects, including Spring Valley Village and The Ashby at McLean. The total value of these projects, which has not yet been placed in service, is $5.5 million at December 31, 2017 . The following is a reconciliation of real estate assets and accumulated depreciation for the three years ended December 31, 2017 (in thousands): Year Ended December 31, 2017 2016 2015 Real estate assets Balance, beginning of period $ 2,725,635 $ 2,673,891 $ 2,547,188 Additions: Property acquisitions (1) 124,306 240,499 162,702 Improvements (1) 84,560 66,840 50,954 Deductions: Impairment write-down (81,982 ) — (5,909 ) Write-off of disposed assets (2,655 ) (1,272 ) (3,291 ) Property sales (18,181 ) (254,323 ) (77,753 ) Balance, end of period $ 2,831,683 $ 2,725,635 $ 2,673,891 Accumulated depreciation Balance, beginning of period $ 657,425 $ 692,608 $ 640,434 Additions: Depreciation 94,558 88,347 86,536 Deductions: Impairment write-down (48,830 ) — — Write-off of disposed assets (1,708 ) (486 ) (2,408 ) Property sales (11,028 ) (123,044 ) (31,954 ) Balance, end of period $ 690,417 $ 657,425 $ 692,608 (1) Includes non-cash accruals for capital items.

Accounting Policies (Policies)

Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Principles of Consolidation and Basis of Presentation	Principles of Consolidation and Basis of Presentation The accompanying audited consolidated financial statements include the consolidated accounts of Washington REIT and our subsidiaries and entities in which Washington REIT has a controlling financial interest, including where Washington REIT has been determined to be a primary beneficiary of a variable interest entity (“VIE”). See note 3 for additional information on the properties for which there is a noncontrolling interest. All intercompany balances and transactions have been eliminated in consolidation. We have prepared the accompanying audited consolidated financial statements pursuant to the rules and regulations of the Securities and Exchange Commission.
Use of Estimates in the Financial Statements	Use of Estimates in the Financial Statements The preparation of financial statements in conformity with Generally Accepted Accounting Principles ("GAAP") requires management to make certain 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.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Pronouncements Adopted In November 2016, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) 2016-18, Statement of Cash Flows (Topic 230) - Restricted Cash , which requires that restricted cash and cash equivalents be included with cash and cash equivalents when reconciling beginning-of-period and end-of-period total amounts shown on the consolidated statements of cash flows. The new standard is effective for public entities for fiscal years beginning after December 15, 2017 and for interim periods therein, with early adoption permitted. We adopted ASU 2016-18 as of December 31, 2017. The impact of the implementation was as follows: Year Ended December 31, 2017 2016 2015 Net cash provided by operating activities (prior to adoption of ASU 2016-18) $ 130,715 $ 116,931 $ 109,426 Impact of including restricted cash with cash and cash equivalents (89 ) (2,206 ) (108 ) Net cash provided by operating activities (after adoption of ASU 2016-18) $ 130,626 $ 114,725 $ 109,318 Net cash used in investing activities (prior to adoption of ASU 2016-18) $ (192,902 ) $ (58,632 ) $ (93,018 ) Impact of including restricted cash with cash and cash equivalents (3,452 ) (4,860 ) 3,192 Net cash used in investing activities (after adoption of ASU 2016-18) $ (196,354 ) $ (63,492 ) $ (89,826 ) Pronouncements Not Yet Adopted In August 2017, the FASB 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. The transition guidance provides companies with the option of early adopting the new standard using a modified retrospective transition method in any interim period after issuance of the update, or alternatively requires adoption for fiscal years beginning after December 15, 2018. We adopted the new standard as of January 1, 2018 and adoption does not have a material impact on our consolidated financial statements. In May 2017, the FASB issued ASU 2017-09, Compensation - Stock Compensation (Topic 718) - Scope of Modification Accounting, which provides guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting. The new standard is effective for all entities for fiscal years beginning after December 15, 2017 and for interim periods therein, with early adoption permitted. We adopted the new standard as of January 1, 2018 and adoption does not have a material impact on our consolidated financial statements. In August 2016, the FASB issued ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments , which provides specific guidance on how cash receipts and payments should be presented and classified in the statement of cash flows for eight specific issues. The new standard is effective for public entities for fiscal years beginning after December 15, 2017 and for interim periods therein, with early adoption permitted. We adopted the new standard as of January 1, 2018 and adoption does not have a material impact on our consolidated financial statements. In June 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”), which creates a single source of revenue guidance. The new standard provides accounting guidance for all revenue arising from contracts with customers and affects all entities that enter into contracts to provide goods or services to their customers (unless the contracts are in the scope of other U.S. generally accepted accounting principles (“GAAP”) requirements, such as the leasing literature). The guidance also provides a model for the measurement and recognition of gains and losses on the sale of certain nonfinancial assets, such as property and equipment, including real estate. The new standard is effective for public entities for fiscal years beginning after December 15, 2017 and for interim periods therein. We adopted the new standard for the fiscal year beginning on January 1, 2018. We evaluated the requirements for recognition of revenue from contracts with customers and measuring gains and losses on the sale of properties in accordance with ASU 2014-09 and concluded that adoption of the new standard will not impact the amount or timing of our revenue recognition. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) (“ASU 2016-02”) , which amends existing accounting standards for lease accounting, including by requiring lessees to recognize most leases on the balance sheet and making certain changes to lessor accounting. The new standard is effective for public entities for fiscal years beginning after December 15, 2018 and for interim periods therein with early adoption permitted. Upon adoption, for leases in which we are the lessor, the lease contract will be separated into lease and non-lease components in accordance with the provisions outlined within ASU 2014-09. The lease component of the contract will be recognized on a straight-line basis in accordance with ASU 2016-02, while the non-lease component will be recognized under the provisions of ASU 2014-09. For lease contracts with a duration of more than one year in which we are the lessee, the present value of future lease payments will be recognized on our balance sheet as a right-of-use asset and a corresponding lease liability. Also, only direct leasing costs may be capitalized under the new standard, while current accounting standards allow for the capitalization of indirect leasing costs. We are currently evaluating the impact ASU 2016-02 may have on Washington REIT’s consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, Measurement of Credit Losses on Financial Instruments , which requires financial assets measured at an amortized cost basis, including trade receivables, to be presented at the net amount expected to be collected. The new standard is effective for public entities for fiscal years beginning after December 15, 2019 and for interim periods therein with adoption one year earlier permitted. We are currently evaluating the impact the new standard may have on Washington REIT’s consolidated financial statements.
Revenue Recognition	Revenue Recognition We lease multifamily properties under operating leases with terms of generally one year or less. We lease commercial properties (our office and retail segments) under operating leases with an average term of seven years. Substantially all commercial leases contain fixed escalations or, in some instances, changes based on the Consumer Price Index, which occur at specified times during the term of the lease. We recognize rental income and rental abatements from our multifamily and commercial leases when earned on a straight-line basis over the lease term. Recognition of rental income commences when control of the leased space has been given to the tenant. We recognize sales of real estate at closing only when sufficient down payments have been obtained, possession and other attributes of ownership have been transferred to the buyer and we have no significant continuing involvement. We recognize cost reimbursement income from pass-through expenses on an accrual basis over the periods in which the expenses were incurred. Pass-through expenses are comprised of real estate taxes, operating expenses and common area maintenance costs which are reimbursed by tenants in accordance with specific allowable costs per tenant lease agreements. Parking revenues are derived from leases, monthly parking agreements and transient parking. We recognize parking revenues from leases on a straight-line basis over the lease term and other parking revenues as earned.
Accounts Receivable and Allowance for Doubtful Accounts	Accounts Receivable and Allowance for Doubtful Accounts Accounts receivable primarily represents amounts accrued and unpaid from tenants in accordance with the terms of the respective leases, subject to our revenue recognition policy. We review receivables monthly and establish reserves when, in the opinion of management, collection of the receivable is doubtful. We establish reserves for tenants whose rent payment histories or financial conditions cast doubt upon the tenants’ abilities to perform under their lease obligations. When we determine the collection of a receivable to be doubtful in the same quarter that we established the receivable, we recognize the allowance for that receivable as an offset to real estate revenues. When we determine a receivable that was initially established in a prior quarter to be doubtful, we recognize the allowance as an operating expense in Real estate expenses in the consolidated statements of income. In addition to rents due currently, accounts receivable include amounts representing minimal rental income accrued on a straight-line basis to be paid by tenants over the remaining term of their respective leases. Our accounts receivable balances include $0.4 million and $2.4 million of notes receivable as of December 31, 2017 and 2016 , respectively. The decrease is due to the repayment during the fourth quarter of 2017 of a note receivable acquired in 2008 with the purchase of 2445 M Street.
Debt Issuance Costs	Debt Issuance Costs We amortize external debt issuance costs using the effective interest rate method or the straight-line method which approximates the effective interest rate method, over the estimated life of the related debt. We record debt issuance costs related to notes and mortgage notes, net of amortization, on our consolidated balance sheets as an offset to their related debt. We record debt issuance costs related to revolving lines of credit on our consolidated balance sheets with Prepaid expenses and other assets, regardless of whether a balance on the line of credit is outstanding. We record the amortization of all debt issuance costs as interest expense.
Deferred Leasing Costs	Deferred Leasing Costs We capitalize and amortize costs associated with the successful negotiation of leases, both external commissions and internal direct costs, on a straight-line basis over the terms of the respective leases. We record the amortization of deferred leasing costs in Depreciation and amortization on the consolidated statements of income. If an applicable lease terminates prior to the expiration of its initial lease term, we write off the carrying amount of the costs to amortization expense. We capitalize and amortize against revenue leasing incentives associated with the successful negotiation of leases on a straight-line basis over the terms of the respective leases. We record the amortization of deferred leasing incentives as a reduction of revenue. If an applicable lease terminates prior to the expiration of its initial lease term, we write off the carrying amount of the costs as a reduction of revenue.
Real Estate and Depreciation	Real Estate and Depreciation We depreciate buildings on a straight-line basis over estimated useful lives ranging from 28 to 50 years. We capitalize all capital improvements associated with replacements, improvements or major repairs to real property that extend its useful life and depreciate them using the straight-line method over their estimated useful lives ranging from 3 to 30 years. We also capitalize costs incurred in connection with our development projects, including capitalizing interest incurred on borrowing obligations and other internal costs during periods in which qualifying expenditures have been made and activities necessary to get the development projects ready for their intended use are in progress. Capitalization of these costs begin when the activities and related expenditures commence and cease when the project is substantially complete and ready for its intended use, at which time the project is placed in service and depreciation commences. In addition, we capitalize tenant leasehold improvements when certain criteria are met, including when we supervise construction and will own the improvements. We depreciate all tenant improvements over the shorter of the useful life of the improvements or the term of the related tenant lease. Real estate depreciation expense from continuing operations was $90.1 million , $84.1 million , $80.7 million during the years ended December 31, 2017 , 2016 and 2015 , respectively. We charge maintenance and repair costs that do not extend an asset’s useful life to expense as incurred. Interest expense and interest capitalized to real estate assets related to development and major renovation activities for the three years ended December 31, 2017 were as follows (in thousands): Year Ended December 31, 2017 2016 2015 Total interest incurred $ 48,498 $ 53,794 $ 60,204 Capitalized interest (964 ) (668 ) (658 ) Interest expense, net of capitalized interest $ 47,534 $ 53,126 $ 59,546 We recognize impairment losses on long-lived assets used in operations, development assets or land held for future development, if indicators of impairment are present and the net undiscounted cash flows estimated to be generated by those assets are less than the assets' carrying amount and estimated undiscounted cash flows associated with future development expenditures. If such carrying amount is in excess of the estimated undiscounted cash flows from the operation and disposal of the property, we would recognize an impairment loss equivalent to an amount required to adjust the carrying amount to its estimated fair value, calculated in accordance with current GAAP fair value provisions. Assets held for sale are recorded at the lower of cost or fair value less costs to sell. Acquisitions The properties we acquire typically are not businesses as defined by ASU 2017-01, Business Combinations (Topic 805) - Clarifying the Definition of a Business . Per this definition, a set of transferred assets and activities is not a business when substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or group of similar identifiable assets. We therefore account for such acquisitions as asset acquisitions. Acquisition costs are capitalized and identifiable assets (including physical assets and in-place leases), liabilities assumed and any noncontrolling interests are measured by allocating the cost of the acquisition on a relative fair value basis. Acquisitions executed prior to our adoption of ASU 2017-01 as of January 1, 2017 were accounted for as business combinations. We determine the fair values of acquired buildings on an “as-if-vacant” basis considering a variety of factors, including the replacement cost of the property, estimated rental and absorption rates, estimated future cash flows and valuation assumptions consistent with current market conditions. We determine the fair value of land acquired based on comparisons to similar properties that have been recently marketed for sale or sold. The fair value of in-place leases consists of the following components – (a) the estimated cost to us to replace the leases, including foregone rents during the period of finding a new tenant and foregone recovery of tenant pass-throughs (referred to as “absorption cost”); (b) the estimated cost of tenant improvements, and other direct costs associated with obtaining a new tenant (referred to as “tenant origination cost”); (c) estimated leasing commissions associated with obtaining a new tenant (referred to as “leasing commissions”); (d) the above/at/below market cash flow of the leases, determined by comparing the projected cash flows of the leases in place, including consideration of renewal options, to projected cash flows of comparable market-rate leases (referred to as “net lease intangible”); and (e) the value, if any, of customer relationships, determined based on our evaluation of the specific characteristics of each tenant’s lease and our overall relationship with the tenant (referred to as “customer relationship value”). We have attributed no value to customer relationships as of December 31, 2017 and 2016 . We discount the amounts used to calculate net lease intangibles using an interest rate which reflects the risks associated with the leases acquired. We classify tenant origination costs as income producing property on our consolidated balance sheets and amortize the tenant origination costs as depreciation expense on a straight-line basis over the remaining life of the underlying leases. We classify leasing commissions and absorption costs as other assets and amortize leasing commissions and absorption costs as amortization expense on a straight-line basis over the remaining life of the underlying leases. We classify net lease intangible assets as other assets and amortize them on a straight-line basis as a decrease to real estate rental revenue over the remaining term of the underlying leases. We classify net lease intangible liabilities as other liabilities and amortize them on a straight-line basis as an increase to real estate rental revenue over the remaining term of the underlying leases. If any of the fair value of below market lease intangibles includes fair value associated with a renewal option, such amounts are not amortized until the renewal option is executed, else the related value is expensed at that time. Should a tenant terminate its lease, we accelerate the amortization of the unamortized portion of the tenant origination cost, leasing commissions, absorption costs and net lease intangible associated with that lease, over its new, shorter term. Balances, net of accumulated depreciation or amortization, as appropriate, of the components of the fair value of in-place leases at December 31, 2017 and 2016 were as follows (in thousands): December 31, 2017 2016 Gross Carrying Value Accumulated Amortization Net Gross Carrying Value Accumulated Amortization Net Tenant origination costs $ 66,378 $ 50,157 $ 16,221 $ 54,352 $ 44,823 $ 9,529 Leasing commissions/absorption costs 123,992 95,115 28,877 101,311 86,210 15,101 Net lease intangible assets 19,362 16,089 3,273 18,903 14,193 4,710 Net lease intangible liabilities 43,230 28,174 15,056 33,687 25,359 8,328 Below-market ground lease intangible asset 12,080 1,903 10,177 12,080 1,714 10,366 Amortization of these combined components during the three years ended December 31, 2017 , 2016 and 2015 was as follows (in thousands): Year Ended December 31, 2017 2016 2015 Depreciation and amortization expense $ 14,911 $ 17,655 $ 22,244 Real estate rental revenue (increase) decrease, net (922 ) 410 538 $ 13,989 $ 18,065 $ 22,782 Amortization of these combined components over the next five years is projected to be as follows (in thousands): Depreciation and amortization expense Real estate rental revenue, net increase Total 2018 $ 13,456 $ (1,574 ) $ 11,882 2019 6,485 (1,633 ) 4,852 2020 4,905 (1,335 ) 3,570 2021 3,729 (1,191 ) 2,538 2022 3,058 (1,155 ) 1,903 Thereafter 23,642 (4,895 ) 18,747
Internal Use Software, Policy [Policy Text Block]	Software Developed for Internal Use The costs of software developed for internal use that qualify for capitalization are included with Prepaid expenses and other assets on our consolidated balance sheets. These capitalized costs include external direct costs utilized in developing or obtaining the applications and expenses for employees who are directly associated with the development of the applications. Capitalization of such costs begins when the preliminary project stage is complete and continues until the project is substantially complete and is ready for its intended purpose. Completed projects are amortized on a straight-line basis over their estimated useful lives.
Discontinued Operations	Discontinued Operations We classify properties as held for sale when they meet the necessary criteria, which include: (a) senior management commits to and actively embarks upon a plan to sell the assets, (b) the sale is expected to be completed within one year under terms usual and customary for such sales and (c) actions required to complete the plan indicate that it is unlikely that significant changes to the plan will be made or that the plan will be withdrawn. We generally consider that a property has met these criteria when a sale of the property has been approved by the board of trustees, or a committee with authorization from the board of trustees, there are no known significant contingencies related to the sale and management believes it is probable that the sale will be completed within one year. Depreciation on these properties is discontinued at the time they are classified as held for sale, but operating revenues, operating expenses and interest expense continue to be recognized until the date of sale. Revenues and expenses of properties that are either sold or classified as held for sale are presented as discontinued operations for all periods presented in the consolidated statements of income if the dispositions represent a strategic shift that has (or will have) a major effect on our operations and financial results. Interest on debt that can be identified as specifically attributed to these properties is included in discontinued operations. If the dispositions do not represent a strategic shift that has (or will have) a major effect on our operations and financial results, then the revenues and expenses of the properties that are classified as sold or held for sale are presented as continuing operations in the consolidated statements of income for all periods presented.
Segments	Segments We evaluate performance based upon net operating income from the combined properties in each segment. Our reportable operating segments are consolidations of similar properties. GAAP requires that segment disclosures present the measure(s) used by the chief operating decision maker for purposes of assessing segments’ performance. Net operating income is a key measurement of our segment profit and loss. Net operating income is defined as segment real estate rental revenue less segment real estate expenses.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents include cash and commercial paper with original maturities of 90 days or less. We maintain cash deposits with financial institutions that at times exceed applicable insurance limits. We reduce this risk by maintaining such deposits with high quality financial institutions that management believes are credit-worthy.
Restricted Cash	Restricted Cash Restricted cash includes funds escrowed for tenant security deposits, real estate tax, insurance and mortgage escrows and escrow deposits required by lenders on certain of our properties to be used for future building renovations or tenant improvements.
Earnings Per Common Share	Earnings Per Common Share We determine “Basic earnings per share” using the two-class method as our unvested restricted share awards and units have non-forfeitable rights to dividends, and are therefore considered participating securities. We compute basic earnings per share by dividing net income attributable to the controlling interest less the allocation of undistributed earnings to unvested restricted share awards and units by the weighted-average number of common shares outstanding for the period. We also determine “Diluted earnings per share” under the two-class method with respect to the unvested restricted share awards. We further evaluate any other potentially dilutive securities at the end of the period and adjust the basic earnings per share calculation for the impact of those securities that are dilutive. Our dilutive earnings per share calculation includes the dilutive impact of employee stock options based on the treasury stock method and our performance share units under the contingently issuable method.
Stock Based Compensation	Stock Based Compensation We currently maintain equity based compensation plans for trustees, officers and employees. We recognize compensation expense for service-based share awards ratably over the period from the service inception date through the vesting period based on the fair market value of the shares on the date of grant. If an award's service inception date precedes the grant date, we initially measure compensation expense for awards with performance conditions at fair value at the service inception date based on probability of payout, and we remeasure compensation expense at subsequent reporting dates until all of the award’s key terms and conditions are known and the grant date is established. We amortize awards with performance conditions using the graded expense method. We measure compensation expense for awards with market conditions based on the grant date fair value, as determined using a Monte Carlo simulation, and we amortize the expense ratably over the requisite service period, regardless of whether the market conditions are achieved and the awards ultimately vest. Compensation expense for the trustee grants, which fully vest immediately, is fully recognized upon issuance based upon the fair market value of the shares on the date of grant.
Accounting for Uncertainty in Income Taxes	Accounting for Uncertainty in Income Taxes We can recognize a tax benefit only if it is “more likely than not” that a particular tax position will be sustained upon examination or audit. To the extent that the “more likely than not” standard has been satisfied, the benefit associated with a tax position is measured as the largest amount that is greater than 50% likely of being recognized upon settlement. As of December 31, 2017 and 2016, we did not have any unrecognized tax benefits. We do not believe that there will be any material changes to our uncertain tax positions over the next twelve months. We are subject to federal income tax as well as income tax of the states of Maryland and Virginia, and the District of Columbia. However, as a REIT, we generally are not subject to income tax on our taxable income to the extent it is distributed as dividends to our shareholders. Tax returns filed for 2013 through 2017 tax years are subject to examination by taxing authorities. We classify interest and penalties related to uncertain tax positions, if any, in our financial statements as a component of general and administrative expense.
Derivatives	Derivatives We borrow funds at a combination of fixed and variable rates. Borrowings under our revolving credit facility and term loans bear interest at variable rates. Our interest rate risk management objectives are to minimize interest rate fluctuation on long-term indebtedness and limit the impact of interest rate changes on earnings and cash flows. To achieve these objectives, from time to time, we may enter into interest rate hedge contracts such as collars, swaps, caps and treasury lock agreements in order to mitigate our interest rate risk with respect to various debt instruments. We generally do not hold or issue these derivative contracts for trading or speculative purposes. The interest rate swaps we enter into are recorded at fair value on a recurring basis. We assess effectiveness of our cash flow hedges both at inception and on an ongoing basis. The effective portion of changes in fair value of the interest rate swaps associated with our cash flow hedges is recorded in accumulated other comprehensive income (loss). Our cash flow hedges become ineffective if critical terms of the hedging instrument and the debt instrument such as notional amounts, settlement dates, reset dates, calculation period and LIBOR do not perfectly match. In addition, we evaluate the default risk of the counterparty by monitoring the creditworthiness of the counterparty. When ineffectiveness of a cash flow hedge exists, the ineffective portion of changes in fair value of the interest rate swaps associated with our cash flow hedges is recognized in earnings in the period affected.

Nature of Business (Tables)

Nature of Business (Tables)	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Dispositions	During the three years ended December 31, 2017 , we sold our interests in the following properties (in thousands): Disposition Date Property Type Gain on Sale October 23, 2017 Walker House Apartments Multifamily $ 23,838 Total 2017 $ 23,838 May 26, 2016 Dulles Station II (1) Office $ 527 June 27, 2016 Maryland Office Portfolio Transaction I (2) Office 23,585 September 22, 2016 Maryland Office Portfolio Transaction II (3) Office 77,592 Total 2016 $ 101,704 March 20, 2015 Country Club Towers Multifamily $ 30,277 September 9, 2015 1225 First Street (4) Multifamily — October 21, 2015 Munson Hill Towers Multifamily 51,395 December 14, 2015 Montgomery Village Center Retail 7,981 Total 2015 $ 89,653 (1) Land held for future development and an interest in a parking garage. (2) Maryland Office Portfolio Transaction I consists of 6110 Executive Boulevard, 600 Jefferson Plaza, Wayne Plaza and West Gude Drive. (3) Maryland Office Portfolio Transaction II consists of 51 Monroe Street and One Central Plaza. (4) Interest in land held for future development.
Taxable Percentage of Dividends Paid	The following is a breakdown of the taxable percentage of our dividends for the years ended December 31, 2017, 2016 and 2015 (unaudited): 2017 2016 2015 Ordinary income 76 % 66 % 78 % Return of capital — % 33 % 22 % Qualified dividends 2 % — % — % Unrecaptured Section 1250 gain 8 % 1 % — % Capital gain 14 % — % — %

Accounting Policies (Tables)

Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Schedule of Impact of Implementation of New Accounting Pronouncement	We adopted ASU 2016-18 as of December 31, 2017. The impact of the implementation was as follows: Year Ended December 31, 2017 2016 2015 Net cash provided by operating activities (prior to adoption of ASU 2016-18) $ 130,715 $ 116,931 $ 109,426 Impact of including restricted cash with cash and cash equivalents (89 ) (2,206 ) (108 ) Net cash provided by operating activities (after adoption of ASU 2016-18) $ 130,626 $ 114,725 $ 109,318 Net cash used in investing activities (prior to adoption of ASU 2016-18) $ (192,902 ) $ (58,632 ) $ (93,018 ) Impact of including restricted cash with cash and cash equivalents (3,452 ) (4,860 ) 3,192 Net cash used in investing activities (after adoption of ASU 2016-18) $ (196,354 ) $ (63,492 ) $ (89,826 )
Schedule of Interest and Interest Capitalized	Interest expense and interest capitalized to real estate assets related to development and major renovation activities for the three years ended December 31, 2017 were as follows (in thousands): Year Ended December 31, 2017 2016 2015 Total interest incurred $ 48,498 $ 53,794 $ 60,204 Capitalized interest (964 ) (668 ) (658 ) Interest expense, net of capitalized interest $ 47,534 $ 53,126 $ 59,546
Components of Fair Value of In-Place Leases	Balances, net of accumulated depreciation or amortization, as appropriate, of the components of the fair value of in-place leases at December 31, 2017 and 2016 were as follows (in thousands): December 31, 2017 2016 Gross Carrying Value Accumulated Amortization Net Gross Carrying Value Accumulated Amortization Net Tenant origination costs $ 66,378 $ 50,157 $ 16,221 $ 54,352 $ 44,823 $ 9,529 Leasing commissions/absorption costs 123,992 95,115 28,877 101,311 86,210 15,101 Net lease intangible assets 19,362 16,089 3,273 18,903 14,193 4,710 Net lease intangible liabilities 43,230 28,174 15,056 33,687 25,359 8,328 Below-market ground lease intangible asset 12,080 1,903 10,177 12,080 1,714 10,366 Amortization of these combined components during the three years ended December 31, 2017 , 2016 and 2015 was as follows (in thousands): Year Ended December 31, 2017 2016 2015 Depreciation and amortization expense $ 14,911 $ 17,655 $ 22,244 Real estate rental revenue (increase) decrease, net (922 ) 410 538 $ 13,989 $ 18,065 $ 22,782
Components of Fair Value of In-Place Leases - Future Amortization	Amortization of these combined components over the next five years is projected to be as follows (in thousands): Depreciation and amortization expense Real estate rental revenue, net increase Total 2018 $ 13,456 $ (1,574 ) $ 11,882 2019 6,485 (1,633 ) 4,852 2020 4,905 (1,335 ) 3,570 2021 3,729 (1,191 ) 2,538 2022 3,058 (1,155 ) 1,903 Thereafter 23,642 (4,895 ) 18,747

Real Estate (Tables)

Real Estate (Tables)	12 Months Ended
	Dec. 31, 2017
Real Estate [Abstract]
Schedule of Real Estate Properties	As of December 31, 2017 and 2016 , our real estate investment portfolio classified as held and used, at cost, consists of properties as follows (in thousands): December 31, 2017 2016 Office $ 1,355,033 $ 1,349,378 Multifamily 895,811 885,084 Retail 451,158 450,941 $ 2,702,002 $ 2,685,403
Schedule of Development Costs	The cost of our real estate portfolio under development or held for future development as of December 31, 2017 and 2016 is as follows (in thousands): December 31, 2017 2016 Office $ 680 $ 2,640 Multifamily 49,616 36,013 Retail 4,126 1,579 $ 54,422 $ 40,232
Schedule of Real Estate Properties Acquired	Properties and land for development acquired during the three years ended December 31, 2017 were as follows: Acquisition Date Property Type # of units (unaudited) Rentable Square Feet (unaudited) Contract Purchase Price (in thousands) April 4, 2017 Watergate 600 Office N/A 293,000 $ 135,000 May 20, 2016 Riverside Apartments Multifamily 1,222 N/A $ 244,750 July 1, 2015 The Wellington Multifamily 711 N/A $ 167,000
Schedule of Revenue and Earnings from Acquisition	The revenue and earnings of our acquisitions during their year of acquisition for the three years ended December 31, 2017 are as follows (in thousands): Year Ended December 31, 2017 2016 2015 Real estate rental revenue $ 14,518 $ 13,112 $ 6,797 Net income (loss) 2,226 (1,688 ) (2,748 )
Schedule of Purchase Price of Acquisitions	We recorded the total cost of the above acquisitions as follows (in thousands): 2017 2016 2015 Land $ 45,981 $ 38,924 $ 30,548 Land held for development — 15,968 15,000 Buildings 66,241 184,854 116,563 Tenant origination costs 12,084 — — Leasing commissions/absorption costs 23,161 4,992 4,889 Net lease intangible assets 498 22 — Net lease intangible liabilities (9,585 ) (10 ) — Deferred tax liability (560 ) — — Total $ 137,820 $ 244,750 $ 167,000
Schedule of Assets of Joint Venture	As of December 31, 2016 , The Maxwell joint venture's assets were as follows (in thousands): December 31, 2016 Land $ 12,851 Income producing property 37,949 Accumulated depreciation and amortization (4,571 ) Other assets 456 $ 46,685
Schedule of Liabilities of Joint Venture	As of December 31, 2016 , The Maxwell joint venture's liabilities were as follows (in thousands): December 31, 2016 Mortgage notes payable, net (1) $ 31,869 Accounts payable and other liabilities 186 Tenant security deposits 99 $ 32,154
Schedule of Properties Sold	We sold our interests in the following properties during the three years ended December 31, 2017 : Disposition Date Property Segment # of units (unaudited) Rentable Contract Gain on Sale October 23, 2017 Walker House Apartments Multifamily 212 N/A $ 32,200 $ 23,838 Total 2017 $ 32,200 $ 23,838 May 26, 2016 Dulles Station, Phase II (1) Office N/A N/A $ 12,100 $ 527 June 27, 2016 Maryland Office Portfolio Transaction I (2) Office N/A 692,000 111,500 23,585 September 22, 2016 Maryland Office Portfolio Transaction II (3) Office N/A 491,000 128,500 77,592 Total 2016 1,183,000 $ 252,100 $ 101,704 March 20, 2015 Country Club Towers Multifamily 227 N/A $ 37,800 $ 30,277 September 9, 2015 1225 First Street (4) Multifamily N/A N/A 14,500 — October 21, 2015 Munson Hill Towers Multifamily 279 N/A 57,050 51,395 December 14, 2015 Montgomery Village Center Retail N/A 197,000 27,750 7,981 Total 2015 506 197,000 $ 137,100 $ 89,653 (1) Land held for future development and an interest in a parking garage. (2) Maryland Office Portfolio Transaction I consists of 6110 Executive Boulevard, 600 Jefferson Plaza, Wayne Plaza and West Gude Drive. (3) Maryland Office Portfolio Transaction II consists of 51 Monroe Street and One Central Plaza. (4) Interest in land held for future development.
Schedule of Revenue and Earnings from Disposed Property	Real estate rental revenue and net income for the Maryland Office Portfolio for the three years ended December 31, 2017 are as follows: Year Ending December 31, 2017 2016 2015 Real estate rental revenue $ — $ 20,266 $ 32,423 Net income — 9,376 9,848

Mortgage Notes Payable (Tables)

Mortgage Notes Payable (Tables)	12 Months Ended
	Dec. 31, 2017
Notes Payable, Noncurrent [Abstract]
Schedule of Debt	As of December 31, 2017 and 2016 , we had outstanding mortgage notes payable, each collateralized by one or more buildings and related land from our portfolio, as follows (in thousands): December 31, Properties Assumption/Issuance Date (1) Effective Interest Rate (2) 2017 2016 Payoff Date/Maturity Date Army Navy Building (3) 3/26/2014 3.18 % $ — $ 49,618 2/1/2017 Yale West (4) 2/21/2014 3.75 % 46,629 47,078 1/31/2022 Olney Village Center 8/30/2011 4.94 % 13,091 14,851 10/1/2023 Kenmore Apartments (5) 2/2/2009 5.37 % 32,194 32,938 9/1/2018 91,914 144,485 Premiums and discounts, net 3,385 4,354 Debt issuance costs, net (158 ) (299 ) $ 95,141 $ 148,540 (1) Each of these mortgages was assumed with the acquisition of the collateralized properties, except for the mortgage note secured by Kenmore Apartments, which was originally executed by Washington REIT. We record mortgages assumed in an acquisition at fair value. (2) Yield on the assumption/issuance date, including the effects of any premiums, discounts or fair value adjustments on the notes. (3) The note was prepaid without penalty in February 2017. (4) The maturity date of the mortgage note is January 1, 2052, but can be prepaid, without penalty, beginning on January 31, 2022. (5) The maturity date of the mortgage note is March 1, 2019, but can be prepaid, without penalty, beginning on September 1, 2018.
Schedule of Maturities of Long-term Debt	Scheduled principal payments subsequent to December 31, 2017 are as follows (in thousands): 2018 $ 34,544 2019 2,500 2020 2,659 2021 2,829 2022 46,984 Thereafter 2,398 $ 91,914 The required principal payments as of December 31, 2017 are as follows (in thousands): 2018 $ — 2019 — 2020 250,000 2021 150,000 2022 300,000 Thereafter 200,000 $ 900,000

Unsecured Lines Of Credit Pay33

Unsecured Lines Of Credit Payable (Tables)	12 Months Ended
	Dec. 31, 2017
Unsecured Debt [Abstract]
Schedule of Revolving Credit Facilities Covenant Compliance	For the three years ended December 31, 2017 , we recognized interest expense (excluding facility fees) and facility fees as follows (in thousands): Year Ended December 31, 2017 2016 2015 Interest expense (excluding facility fees) $ 3,857 $ 3,272 $ 2,266 Facility fees 1,217 1,220 1,241 The amount of the Revolving Credit Facility unused and available at December 31, 2017 was as follows (in thousands): Committed capacity $ 600,000 Borrowings outstanding (166,000 ) Unused and available $ 434,000 We executed borrowings and repayments on the Revolving Credit Facility during 2017 as follows (in thousands): Balance at December 31, 2016 $ 120,000 Borrowings 274,000 Repayments (228,000 ) Balance at December 31, 2017 $ 166,000 Information related to revolving credit facilities for the three years ended December 31, 2017 as follows (in thousands, except percentage amounts): Year Ended December 31, 2017 2016 2015 Total revolving credit facilities at December 31 $ 600,000 $ 600,000 $ 600,000 Borrowings outstanding at December 31 166,000 120,000 105,000 Weighted average daily borrowings during the year 179,633 214,962 167,573 Maximum daily borrowings during the year 252,000 358,000 350,000 Weighted average interest rate during the year 2.15 % 1.52 % 1.35 % Weighted average interest rate on borrowings outstanding at December 31 2.54 % 1.64 % 1.36 %

Notes Payable (Tables)

Notes Payable (Tables)	12 Months Ended
	Dec. 31, 2017
Notes Payable [Abstract]
Schedule of Long-term Debt Instruments	Our unsecured notes outstanding as of December 31, 2017 are as follows (in thousands): Coupon/Stated Rate Effective Rate (1) Principal Amount Maturity Date (2) 10 Year Unsecured Notes 4.95 % 5.05 % $ 250,000 10/1/2020 2015 Term Loan 1 Month LIBOR + 110 basis points 2.72 % 150,000 3/15/2021 10 Year Unsecured Notes 3.95 % 4.02 % 300,000 10/15/2022 2016 Term Loan 1 Month LIBOR + 165 basis points 2.86 % 150,000 7/21/2023 30 Year Unsecured Notes 7.25 % 7.36 % 50,000 2/25/2028 Total principal 900,000 Premiums and discounts, net (1,580 ) Deferred issuance costs, net (4,062 ) Total $ 894,358 (1) For fixed rate notes, the effective rate represents the yield on issuance date, including the effects of discounts on the notes. For variable rate notes, the effective rate represents the rate as fixed by interest rate derivatives (see note 7 ). (2) No principal amounts are due prior to maturity.
Schedule of Maturities of Long-term Debt	Scheduled principal payments subsequent to December 31, 2017 are as follows (in thousands): 2018 $ 34,544 2019 2,500 2020 2,659 2021 2,829 2022 46,984 Thereafter 2,398 $ 91,914 The required principal payments as of December 31, 2017 are as follows (in thousands): 2018 $ — 2019 — 2020 250,000 2021 150,000 2022 300,000 Thereafter 200,000 $ 900,000

Derivative Instruments (Tables)

Derivative Instruments (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Derivative Instruments	The fair values of the interest rate swaps as of December 31, 2017 and 2016 , are as follows (in thousands): Aggregate Notional Amount Effective Date Fair Value Asset Derivatives December 31, Derivative Instrument Maturity Date 2017 2016 Interest rate swaps $ 150,000 October 15, 2015 March 15, 2021 $ 1,987 $ 417 Interest rate swaps 150,000 March 31, 2017 July 21, 2023 7,432 7,194 $ 300,000 $ 9,419 $ 7,611 We record interest rate swaps on our consolidated balance sheets with prepaid expenses and other assets when in a net asset position, and with accounts payable and other liabilities when in a net liability position. The interest rate swaps have been effective since inception. The gains or losses on the effective swaps are recognized in other comprehensive income (loss), as follows (in thousands): Year Ending December 31, 2017 2016 2015 Unrealized gain (loss) on interest rate hedges $ 1,808 $ 8,161 $ (550 )

Fair Value Disclosures (Tables)

Fair Value Disclosures (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Financial Assets And Liabilities Measured At Fair Value	The fair values of these assets and liabilities at December 31, 2017 and 2016 were as follows (in thousands): December 31, 2017 December 31, 2016 Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: SERP $ 1,858 $ — $ 1,858 $ — $ 1,407 $ — $ 1,407 $ — Interest rate swaps 9,419 — 9,419 — 7,611 — 7,611 —
Financial Assets And Liabilities Not Measured At Fair Value	As of December 31, 2017 and 2016 , the carrying values and estimated fair values of our financial instruments were as follows (in thousands): December 31, 2017 2016 Carrying Value Fair Value Carrying Value Fair Value Cash and cash equivalents $ 9,847 $ 9,847 $ 11,305 $ 11,305 Restricted cash 2,776 2,776 6,317 6,317 2445 M Street note receivable — — 2,089 2,173 Mortgage notes payable 95,141 97,181 148,540 149,997 Lines of credit payable 166,000 166,000 120,000 120,000 Notes payable 894,358 931,377 843,084 873,516

Stock Based Compensation (Table

Stock Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Share-based Compensation [Abstract]
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions	The assumptions used to value the officer LTIP awards were as follows: 2017 Awards 2016 Awards 2015 Awards Expected volatility (1) 18.5% - 18.7% 18.2 % 17.2% - 17.5% Risk-free interest rate (2) 1.5 % 1.3 % 1.0% - 1.1% Expected term (3) 3 and 4 years 3 and 4 years 3 and 4 years Share price at grant date $30.84 - $32.69 $27.06 $27.66 - $27.76 (1) Expected volatility based upon historical volatility of our daily closing share price. (2) Risk-free interest rate based on U.S. treasury constant maturity bonds on the measurement date with a maturity equal to the market condition performance period. (3) Expected term based on the market condition performance period.
Schedule of Restricted Share Awards	The activity for the three years ended December 31, 2017 related to our restricted share awards, excluding those subject to market conditions, was as follows: Shares Wtd Avg Grant Fair Value Unvested at December 31, 2014 93,667 $ 25.22 Granted 251,642 27.80 Vested during year (212,856 ) 27.18 Forfeited (26,309 ) 26.77 Unvested at December 31, 2015 106,144 27.71 Granted 251,694 26.01 Vested during year (211,771 ) 29.21 Forfeited (38,368 ) 26.14 Unvested at December 31, 2016 107,699 26.47 Granted 330,639 32.46 Vested during year (194,569 ) 30.50 Forfeited (7,075 ) 27.43 Unvested at December 31, 2017 236,694 27.96
Performance Share Units with Market Conditions	Stock based awards with market conditions under the LTIP were granted in 2017, 2016 and 2015 with fair market values, as determined using a Monte Carlo simulation, as follows (in thousands): Grant Date Fair Value 2017 Awards 2016 Awards 2015 Awards Restricted Unrestricted Restricted Unrestricted Restricted Unrestricted Relative TSR $ 222 $ 666 $ 182 $ 546 $ 191 $ 634 Absolute TSR 100 299 82 246 76 254
Schedule Of Unamortized Value Of Awards With Market Conditions	The unamortized value of these awards with market conditions as of December 31, 2017 was as follows (in thousands): 2017 Awards 2016 Awards 2015 Awards Restricted Unrestricted Restricted Unrestricted Restricted Unrestricted Relative TSR $ 166 $ 444 $ 117 $ 314 $ 83 $ 165 Absolute TSR 75 199 53 142 33 66

Earnings Per Common Share (Tabl

Earnings Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Computation of Basic and Diluted Earnings Per Share	The computation of basic and diluted earnings per share for the three years ended December 31, 2017 was as follows (in thousands; except per share data): Year Ended December 31, 2017 2016 2015 Numerator: Net income $ 19,612 $ 119,288 $ 89,187 Net loss attributable to noncontrolling interests 56 51 553 Allocation of undistributed earnings to unvested restricted share awards and units to continuing operations (362 ) (310 ) (269 ) Adjusted net income attributable to the controlling interests $ 19,306 $ 119,029 $ 89,471 Denominator: Weighted average shares outstanding – basic 76,820 72,163 68,177 Effect of dilutive securities: Operating partnership units 9 — — Employee stock options and restricted share awards 106 176 133 Weighted average shares outstanding – diluted 76,935 72,339 68,310 Basic net income attributable to the controlling interests per common share $ 0.25 $ 1.65 $ 1.31 Diluted net income attributable to the controlling interests per common share $ 0.25 $ 1.65 $ 1.31 Dividends declared per common share $ 1.20 $ 1.20 $ 1.20

Rentals Under Operating Leases

Rentals Under Operating Leases (Tables)	12 Months Ended
	Dec. 31, 2017
Leases, Operating [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases	As of December 31, 2017 , non-cancelable commercial operating leases provide for minimum rental income were as follows (in thousands): 2018 $ 190,391 2019 172,289 2020 157,694 2021 132,150 2022 109,713 Thereafter 376,904 $ 1,139,141

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Real Estate Rental Revenue, Percent	Real estate rental revenue as a percentage of the total for each of the reportable operating segments in continuing operations for the three years ended December 31, 2017 was as follows: Year Ended December 31, 2017 2016 2015 Office 52 % 53 % 57 % Multifamily 29 % 27 % 22 % Retail 19 % 20 % 21 %
Percentage of Real Estate Assets by Segment	The percentage of income producing real estate assets classified as held and used, at cost, for each of the reportable operating segments in continuing operations as of December 31, 2017 and 2016 was as follows: December 31, 2017 2016 Office 50 % 50 % Multifamily 33 % 33 % Retail 17 % 17 %
Reconciliation of Net Operating Income of Reportable Segments	The following tables present revenues, net operating income, capital expenditures and total assets for the three years ended December 31, 2017 from these segments, and reconciles net operating income of reportable segments to net income attributable to the controlling interests as reported (in thousands): Year Ended December 31, 2017 Office Retail Multifamily Corporate Consolidated Real estate rental revenue $ 167,438 $ 62,390 $ 95,250 $ — $ 325,078 Real estate expenses 62,824 15,186 37,640 — 115,650 Net operating income $ 104,614 $ 47,204 $ 57,610 $ — $ 209,428 Depreciation and amortization (112,056 ) General and administrative (22,580 ) Interest expense (47,534 ) Other income 507 Gain on sale of real estate 24,915 Real estate impairment (33,152 ) Income tax benefit 84 Net income 19,612 Less: Net loss attributable to noncontrolling interests 56 Net income attributable to the controlling interests $ 19,668 Capital expenditures $ 30,407 $ 2,128 $ 27,980 $ 3,866 $ 64,381 Total assets $ 1,203,187 $ 346,580 $ 767,279 $ 42,380 $ 2,359,426 Year Ended December 31, 2016 Office Retail Multifamily Corporate and Other Consolidated Real estate rental revenue $ 165,934 $ 61,566 $ 85,764 $ — $ 313,264 Real estate expenses 64,405 15,860 34,748 — 115,013 Net operating income $ 101,529 $ 45,706 $ 51,016 $ — $ 198,251 Depreciation and amortization (108,406 ) General and administrative (19,545 ) Casualty gain 676 Acquisition costs (1,178 ) Interest expense (53,126 ) Other income 297 Gain on sale of real estate 101,704 Income tax benefit 615 Net income 119,288 Less: Net loss attributable to noncontrolling interests 51 Net income attributable to the controlling interests $ 119,339 Capital expenditures $ 30,337 $ 8,821 $ 17,936 $ 920 $ 58,014 Total assets $ 1,104,589 $ 352,056 $ 762,695 $ 34,279 $ 2,253,619 Year Ended December 31, 2015 Office Retail Multifamily Corporate Consolidated Real estate rental revenue $ 174,378 $ 63,507 $ 68,542 $ — $ 306,427 Real estate expenses 67,228 15,606 29,400 — 112,234 Net operating income $ 107,150 $ 47,901 $ 39,142 $ — $ 194,193 Depreciation and amortization (108,935 ) General and administrative (20,123 ) Real estate impairment (5,909 ) Acquisition costs (2,056 ) Interest expense (59,546 ) Other income 709 Loss on extinguishment of debt (119 ) Gain on sale of real estate 91,107 Income tax expense (134 ) Net income 89,187 Less: Net loss attributable to noncontrolling interests 553 Net income attributable to the controlling interests $ 89,740 Capital expenditures $ 29,745 $ 3,897 $ 7,865 $ 2,129 $ 43,636 Total assets $ 1,265,570 $ 354,123 $ 529,773 $ 41,702 $ 2,191,168

Selected Quarterly Financial 41

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	Unaudited financial data by quarter in each of the years ended December 31, 2017 and 2016 were as follows (in thousands, except for per share data): Quarter (1), (2) First Second Third Fourth 2017 Real estate rental revenue $ 77,501 $ 83,456 $ 82,819 $ 81,302 Net income $ 6,615 $ 7,847 $ 2,813 $ 2,337 Net income attributable to the controlling interests $ 6,634 $ 7,864 $ 2,833 $ 2,337 Net income per share Basic $ 0.09 $ 0.10 $ 0.04 $ 0.03 Diluted $ 0.09 $ 0.10 $ 0.04 $ 0.03 2016 Real estate rental revenue $ 77,137 $ 79,405 $ 79,770 $ 76,952 Net income $ 2,379 $ 31,821 $ 79,662 $ 5,426 Net income attributable to the controlling interests $ 2,384 $ 31,836 $ 79,674 $ 5,445 Net income per share Basic $ 0.03 $ 0.44 $ 1.07 $ 0.07 Diluted $ 0.03 $ 0.44 $ 1.07 $ 0.07 (1) With regard to per share calculations, the sum of the quarterly results may not equal full year results due to rounding. (2) The fourth quarter of 2017 includes gain on sale of real estate classified as continuing operations of $24.9 million . The second and third quarters of 2016 include gains on sale of real estate classified as continuing operations of $24.1 million and $77.6 million , respectively. The third and fourth quarters of 2017 include real estate impairments of $5.0 million and $28.2 million , respectively.

Deferred Costs (Tables)

Deferred Costs (Tables)	12 Months Ended
	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Deferred Leasing Costs and Incentives	As of December 31, 2017 and 2016 , deferred leasing costs and deferred leasing incentives were included in prepaid expenses and other assets as follows (in thousands): December 31, 2017 2016 Gross Carrying Value Accumulated Amortization Net Gross Carrying Value Accumulated Amortization Net Deferred leasing costs $ 68,213 $ 28,523 $ 39,690 $ 58,391 $ 22,748 $ 35,643 Deferred leasing incentives 24,946 11,114 13,832 21,157 8,061 13,096
Schedule of Amortization and Write-Offs of Deferred Leasing Costs and Incentives	Amortization, including write-offs, of deferred leasing costs and deferred leasing incentives from continuing operations for the three years ended December 31, 2017 were as follows (in thousands): Year Ended December 31, 2017 2016 2015 Deferred leasing costs amortization $ 6,418 $ 6,076 $ 5,983 Deferred leasing incentives amortization 3,163 2,994 2,848

Nature of Business - Narrative

Nature of Business - Narrative and Taxable Percentage of Dividends (Details) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Jun. 30, 2017	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of real estate	$ 24,900		$ 77,600	$ 24,100	$ 24,915	$ 101,704	$ 91,107
Percentage of Distribution of Ordinary Taxable Income					90.00%
Income tax benefit (expense)					$ 84	$ 615	$ (134)
Deferred Tax Assets, Investment in Subsidiaries	1,400				$ 1,400
Ordinary income					76.00%	66.00%	78.00%
Return of capital					0.00%	33.00%	22.00%
Qualified dividends					2.00%	0.00%	0.00%
Unrecaptured Section 1250 gain					8.00%	1.00%	0.00%
Capital gain					14.00%	0.00%	0.00%
Taxable Reit Subsidiary [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income tax benefit (expense)		$ (700)				$ 600	$ (100)
Deferred Tax Assets, Net						500
Deferred Tax Liabilities	0				$ 0	400
Valuation Allowance of Deferred Tax Assets [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Valuation Allowances and Reserves, Balance						$ 2,882	$ 5,705	$ 5,714
Valuation Allowance of Deferred Tax Assets [Member] | Taxable Reit Subsidiary [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Valuation Allowances and Reserves, Balance	1,413				1,413
Watergate 600 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Deferred Tax Liabilities, Property, Plant and Equipment	$ 560				$ 560

Nature of Business - Properties

Nature of Business - Properties Sold (Details) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Dec. 31, 2017	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of real estate	$ 24,900	$ 77,600	$ 24,100	$ 24,915	$ 101,704	$ 91,107
Gains (Losses) on Sales of Investment Real Estate				$ 23,838	$ 101,704	$ 89,653

Accounting Policies - Effect of

Accounting Policies - Effect of Pronouncements Adopted (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by (used in) operating activities	$ 130,626	$ 114,725	$ 109,318
Net cash provided by (used in) investing activities	(196,354)	(63,492)	(89,826)
Accounting Standards Update 2016-18 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by (used in) operating activities	130,626	114,725	109,318
Net cash provided by (used in) investing activities	(196,354)	(63,492)	(89,826)
Previously Reported [Member] | Accounting Standards Update 2016-18 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by (used in) operating activities	130,715	116,931	109,426
Net cash provided by (used in) investing activities	(192,902)	(58,632)	(93,018)
Reclassification Adjustment [Member] | Accounting Standards Update 2016-18 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by (used in) operating activities	(89)	(2,206)	(108)
Net cash provided by (used in) investing activities	$ (3,452)	$ (4,860)	$ 3,192

Accounting Policies - Revenue R

Accounting Policies - Revenue Recognition and Accounts Receivable and Allowance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property Subject to or Available for Operating Lease [Line Items]
Notes receivable, net	$ 0.4	$ 2.4
Office and Retail
Property Subject to or Available for Operating Lease [Line Items]
Lessor, Operating Lease, Term of Contract	7 years

Accounting Policies - Real Esta

Accounting Policies - Real Estate and Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Real estate depreciation	$ 90,100	$ 84,100	$ 80,700
Total interest incurred	48,498	53,794	60,204
Capitalized interest	(964)	(668)	(658)
Interest expense, net of capitalized interest	$ 47,534	$ 53,126	$ 59,546
Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful Life	3 years
Minimum [Member] | Building [Member]
Property, Plant and Equipment [Line Items]
Useful Life	28 years
Minimum [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Useful Life	3 years
Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful Life	50 years
Maximum [Member] | Building [Member]
Property, Plant and Equipment [Line Items]
Useful Life	50 years
Maximum [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Useful Life	30 years

Accounting Policies - Fair Valu

Accounting Policies - Fair Value of In Place Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Tenant Origination Costs [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	$ 66,378	$ 54,352
Finite-Lived Intangible Assets, Accumulated Amortization	50,157	44,823
Finite-Lived Intangible Assets, Net	16,221	9,529
Leasing Commissions Absorption Costs [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	123,992	101,311
Finite-Lived Intangible Assets, Accumulated Amortization	95,115	86,210
Finite-Lived Intangible Assets, Net	28,877	15,101
Net Lease Intangible Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	19,362	18,903
Finite-Lived Intangible Assets, Accumulated Amortization	16,089	14,193
Finite-Lived Intangible Assets, Net	3,273	4,710
Net Lease Intangible Liabilities Member
Acquired Finite-Lived Intangible Assets [Line Items]
Below Market Lease, Gross	43,230	33,687
Below Market Lease, Accumulated Amortization	28,174	25,359
Below Market Lease, Net	15,056	8,328
Leases, Acquired-in-Place, Below-Market Ground Lease [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	12,080	12,080
Finite-Lived Intangible Assets, Accumulated Amortization	1,903	1,714
Finite-Lived Intangible Assets, Net	$ 10,177	$ 10,366

Accounting Policies - Amortizat

Accounting Policies - Amortization of Leased Assets Acquired (Details) - Leases, Acquired-in-Place [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Amortization of Intangible Assets	$ 14,911	$ 17,655	$ 22,244
Amortization of above and below Market Leases	(922)	410	538
Finite-Lived Intangible Assets, Amortization Expense, Net of Revenue	$ 13,989	$ 18,065	$ 22,782

Accounting Policies - Acquired

Accounting Policies - Acquired Finite-lived Intangible Assets (Details) $ in Thousands	Dec. 31, 2017USD ($)
Real estate rental revenue, net increase
2,018	$ (190,391)
2,019	(172,289)
2,020	(157,694)
2,021	(132,150)
2,022	(109,713)
Thereafter	(376,904)
Leases, Acquired-in-Place [Member]
Depreciation and amortization expense
2,018	13,456
2,019	6,485
2,020	4,905
2,021	3,729
2,022	3,058
Thereafter	23,642
Real estate rental revenue, net increase
2,018	(1,574)
2,019	(1,633)
2,020	(1,335)
2,021	(1,191)
2,022	(1,155)
Thereafter	(4,895)
Total
2,018	11,882
2,019	4,852
2,020	3,570
2,021	2,538
2,022	1,903
Thereafter	$ 18,747

Real Estate - Real Estate Inves

Real Estate - Real Estate Investment Portfolio (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Real Estate [Line Items]
Real estate investment property, at cost	$ 2,702,002	$ 2,685,403
Properties under development or held for future development	54,422	40,232
Office [Member]
Real Estate [Line Items]
Real estate investment property, at cost	1,355,033	1,349,378
Properties under development or held for future development	680	2,640
Multifamily [Member]
Real Estate [Line Items]
Real estate investment property, at cost	895,811	885,084
Properties under development or held for future development	49,616	36,013
Retail [Member]
Real Estate [Line Items]
Real estate investment property, at cost	451,158	450,941
Properties under development or held for future development	4,126	1,579
The Army Navy Club Building [Member]
Real Estate [Line Items]
Properties under development or held for future development	4,800
The Trove [Member]
Real Estate [Line Items]
Properties under development or held for future development	29,700
Riverside Developments [Member]
Real Estate [Line Items]
Properties under development or held for future development	19,200	$ 19,200
Spring Vally Retail Center [Member]
Real Estate [Line Items]
Properties under development or held for future development	$ 3,600

Real Estate - Schedule of Acqui

Real Estate - Schedule of Acquisitions (Details) $ in Thousands		Dec. 31, 2017USD ($)ft²	Apr. 04, 2017USD ($)ft²	Dec. 31, 2016USD ($)	May 20, 2016USD ($)unit	Jul. 01, 2015USD ($)unit
Real Estate [Line Items]
Rentable Square Feet | ft²	[1]	9,948,000
Real estate investment property, at cost		$ 2,702,002		$ 2,685,403
Watergate 600 [Member]
Real Estate [Line Items]
Rentable Square Feet | ft²			293,000
Real estate investment property, at cost			$ 135,000
Riverside Apartments [Member]
Real Estate [Line Items]
Number of Units | unit					1,222
Real estate investment property, at cost				$ 244,750	$ 244,750
The Wellington [Member]
Real Estate [Line Items]
Number of Units | unit						711
Real estate investment property, at cost						$ 167,000
[1]	As of December 31, 2017, Washington REIT had under development multifamily properties, the Wellington land parcel (Trove) and Riverside Apartments land parcel. The value not yet placed into service at December 31, 2017 was $29.7 million and $19.2 million, respectively.

Real Estate - Revenue and Earni

Real Estate - Revenue and Earnings of Acquisitions (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Real Estate [Line Items]
Real estate rental revenue	$ 81,302	$ 82,819	$ 83,456	$ 77,501	$ 76,952	$ 79,770	$ 79,405	$ 77,137	$ 325,078	$ 313,264	$ 306,427
Net income (loss)	$ 2,337	$ 2,813	$ 7,847	$ 6,615	$ 5,426	$ 79,662	$ 31,821	$ 2,379	19,612	119,288	89,187
Watergate 600 [Member]
Real Estate [Line Items]
Real estate rental revenue									14,518
Net income (loss)									$ 2,226
Riverside Apartments [Member]
Real Estate [Line Items]
Real estate rental revenue										13,112
Net income (loss)										$ (1,688)
The Wellington [Member]
Real Estate [Line Items]
Real estate rental revenue											6,797
Net income (loss)											$ (2,748)

Real Estate - Cost of Asset Acq

Real Estate - Cost of Asset Acquisitions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Apr. 04, 2017	May 20, 2016	Jul. 01, 2015
Real Estate [Line Items]
Leasing commissions/absorption costs	$ 68,213	$ 58,391
Real estate investment property, at cost	2,702,002	2,685,403
Watergate 600 [Member]
Real Estate [Line Items]
Land	45,981
Land held for development	0
Buildings	66,241
Tenant origination costs	12,084
Leasing commissions/absorption costs	23,161
Net lease intangible assets	498
Net lease intangible liabilities	9,585
Deferred tax liability	(560)
Total	$ 137,820
Real estate investment property, at cost				$ 135,000
Riverside Apartments [Member]
Real Estate [Line Items]
Land		38,924
Land held for development		15,968
Buildings		184,854
Tenant origination costs		0
Leasing commissions/absorption costs		4,992
Net lease intangible assets		22
Net lease intangible liabilities		10
Deferred tax liability		0
Real estate investment property, at cost		$ 244,750			$ 244,750
The Wellington [Member]
Real Estate [Line Items]
Land			$ 30,548
Land held for development			15,000
Buildings			116,563
Tenant origination costs			0
Leasing commissions/absorption costs			4,889
Net lease intangible assets			0
Net lease intangible liabilities			0
Deferred tax liability			0
Total			$ 167,000
Real estate investment property, at cost						$ 167,000

Real Estate - Acquisitions Narr

Real Estate - Acquisitions Narrative (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Apr. 04, 2017	May 20, 2016	Jul. 01, 2015
Real Estate [Line Items]
Real estate investment property, at cost		$ 2,702,002	$ 2,685,403
Payments to acquire real estate		138,371	227,413	$ 151,917
Watergate 600 [Member]
Real Estate [Line Items]
Real estate investment property, at cost					$ 135,000
Payments to acquire real estate		138,400
Capitalized asset acquisition-related costs		(2,800)
Credit settlement adjustment		$ (1,000)
Issuance of OP Units as consideration in asset acquisition (shares)		12,124
Issuance of OP Units as consideration in asset acquisition		$ 400
Duration for average share price valuation (days)	20 days
Watergate 600 [Member] | Tenant Origination Costs [Member]
Real Estate [Line Items]
Weighted average remaining life (months)		89 months
Watergate 600 [Member] | Leasing Commissions Absorption Costs [Member]
Real Estate [Line Items]
Weighted average remaining life (months)		82 months
Watergate 600 [Member] | Net Lease Intangible Assets [Member]
Real Estate [Line Items]
Weighted average remaining life (months)		13 months
Watergate 600 [Member] | Net Lease Intangible Liability [Member]
Real Estate [Line Items]
Weighted average remaining life (months)		102 months
Riverside Apartments [Member]
Real Estate [Line Items]
Real estate investment property, at cost			244,750			$ 244,750
Payments to acquire real estate			227,400
Credit settlement adjustment			1,400
Riverside Apartments land parcel [Member]
Real Estate [Line Items]
Payments to acquire land			$ 16,000
The Wellington [Member]
Real Estate [Line Items]
Real estate investment property, at cost							$ 167,000
Payments to acquire real estate				151,900
Credit settlement adjustment				100
The Wellington land parcel [Member]
Real Estate [Line Items]
Payments to acquire land				$ 15,000

Real Estate - Variable Interest

Real Estate - Variable Interest Entities Narrative (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended		12 Months Ended
		Jun. 30, 2011	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2015	Nov. 30, 2011
Real Estate [Line Items]
Ownership percentage					95.00%
Impairment of real estate			$ 28,152	$ 5,000
2015 Properties Sold [Member] | Disposed of by Sale, Not Discontinued Operations [Member]
Real Estate [Line Items]
Contract Sale Price					$ 137,100
1225 First Street [Member]
Real Estate [Line Items]
Ownership percentage by noncontrolling owners						5.00%
Impairment of real estate					5,900
1225 First Street [Member] | Multifamily [Member] | 2015 Properties Sold [Member] | Disposed of by Sale, Not Discontinued Operations [Member]
Real Estate [Line Items]
Contract Sale Price	[1]				$ 14,500
The Maxwell [Member]
Real Estate [Line Items]
Ownership percentage		90.00%
Ownership percentage by noncontrolling owners		10.00%
Percentage of joint venture interest acquired			10.00%
Payments to acquire interest in joint venture			$ 4,100
[1]	Interest in land held for future development.

Real Estate - Joint Venture Ass

Real Estate - Joint Venture Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Real Estate [Line Items]
Land	$ 588,025	$ 573,315
Accumulated depreciation and amortization	683,692	657,425
Mortgage notes payable, net	95,141	148,540
Accounts payable and other liabilities	61,565	46,967
Tenant security deposits	$ 9,149	8,802
The Maxwell [Member]
Real Estate [Line Items]
Land		12,851
Income producing property		37,949
Accumulated depreciation and amortization		4,571
Other assets		456
Real Estate Investments, Joint Ventures		46,685
Mortgage notes payable, net		31,869
Accounts payable and other liabilities		186
Tenant security deposits		99
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities		$ 32,154

Real Estate - Properties Sold a

Real Estate - Properties Sold and Held for Sale Narrative (Details) $ in Thousands		3 Months Ended				12 Months Ended
		Dec. 31, 2017USD ($)ft²apartment	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Dec. 31, 2017USD ($)ft²apartment	Dec. 31, 2016USD ($)buildingsContracts	Dec. 31, 2015USD ($)	Jan. 31, 2018USD ($)	Jan. 23, 2018USD ($)
Real Estate [Line Items]
Gain on sale of real estate		$ 24,900		$ 77,600	$ 24,100	$ 24,915	$ 101,704	$ 91,107
Rentable Square Feet | ft²	[1]	9,948,000				9,948,000
Impairment of real estate		$ 28,152	$ 5,000
2017 Properties Sold [Member] | Disposed of by Sale, Not Discontinued Operations [Member]
Real Estate [Line Items]
Contract Sale Price		$ 32,200				$ 32,200
Gain on sale of real estate						$ 23,838
2016 Properties Sold [Member] | Disposed of by Sale, Not Discontinued Operations [Member]
Real Estate [Line Items]
Contract Sale Price							252,100
Gain on sale of real estate							101,704
Walker House [Member] | Multifamily [Member] | 2017 Properties Sold [Member] | Disposed of by Sale, Not Discontinued Operations [Member]
Real Estate [Line Items]
Number of Units | apartment		212				212
Contract Sale Price		$ 32,200				$ 32,200
Gain on sale of real estate						$ 23,838
Braddock Metro Center [Member] | Office [Member]
Real Estate [Line Items]
Rentable Square Feet | ft²		356,000				356,000
Impairment of real estate						$ 9,100
Braddock Metro Center [Member] | Office [Member] | Subsequent Event [Member]
Real Estate [Line Items]
Contract Sale Price									$ 93,000
2445 M Street [Member] | Office [Member]
Real Estate [Line Items]
Rentable Square Feet | ft²		292,000				292,000
Impairment of real estate						$ 24,100
2445 M Street [Member] | Office [Member] | Subsequent Event [Member]
Real Estate [Line Items]
Contract Sale Price										$ 100,000
Dulles Station II [Member] | Office [Member] | 2016 Properties Sold [Member] | Disposed of by Sale, Not Discontinued Operations [Member]
Real Estate [Line Items]
Contract Sale Price	[2]						12,100
Gain on sale of real estate	[3]						$ 527
Maryland Office Portfolio [Member] | Disposed of by Sale, Not Discontinued Operations [Member]
Real Estate [Line Items]
Number of purchase and sale agreements | Contracts							2
Number of buildings sold | buildings							6
Maryland Office Portfolio [Member] | Office [Member] | 2016 Properties Sold [Member] | Disposed of by Sale, Not Discontinued Operations [Member]
Real Estate [Line Items]
Contract Sale Price							$ 240,000
[1]	As of December 31, 2017, Washington REIT had under development multifamily properties, the Wellington land parcel (Trove) and Riverside Apartments land parcel. The value not yet placed into service at December 31, 2017 was $29.7 million and $19.2 million, respectively.
[2]	Land held for future development and an interest in a parking garage.
[3]	Land held for future development and an interest in a parking garage.

Real Estate - Schedule of Prope

Real Estate - Schedule of Properties Sold (Details) $ in Thousands		3 Months Ended			12 Months Ended
		Dec. 31, 2017USD ($)apartment	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Dec. 31, 2017USD ($)apartment	Dec. 31, 2016USD ($)ft²	Dec. 31, 2015USD ($)ft²apartment
Real Estate [Line Items]
Gain on Sale		$ 24,900	$ 77,600	$ 24,100	$ 24,915	$ 101,704	$ 91,107
Disposed of by Sale, Not Discontinued Operations [Member] | 2017 Properties Sold [Member]
Real Estate [Line Items]
Contract Sale Price		$ 32,200			32,200
Gain on Sale					$ 23,838
Disposed of by Sale, Not Discontinued Operations [Member] | 2017 Properties Sold [Member] | Multifamily [Member] | Walker House [Member]
Real Estate [Line Items]
Number of Units | apartment		212			212
Contract Sale Price		$ 32,200			$ 32,200
Gain on Sale					$ 23,838
Disposed of by Sale, Not Discontinued Operations [Member] | 2016 Properties Sold [Member]
Real Estate [Line Items]
Rentable Square Feet Sold | ft²						1,183,000
Contract Sale Price						$ 252,100
Gain on Sale						101,704
Disposed of by Sale, Not Discontinued Operations [Member] | 2016 Properties Sold [Member] | Office [Member] | Dulles Station II [Member]
Real Estate [Line Items]
Contract Sale Price	[1]					12,100
Gain on Sale	[2]					$ 527
Disposed of by Sale, Not Discontinued Operations [Member] | 2016 Properties Sold [Member] | Office [Member] | Maryland Office Portfolio Transaction I [Member]
Real Estate [Line Items]
Rentable Square Feet Sold | ft²						692,000
Contract Sale Price	[3]					$ 111,500
Gain on Sale	[4]					$ 23,585
Disposed of by Sale, Not Discontinued Operations [Member] | 2016 Properties Sold [Member] | Office [Member] | Maryland Office Portfolio Transaction II [Member]
Real Estate [Line Items]
Rentable Square Feet Sold | ft²						491,000
Contract Sale Price	[5]					$ 128,500
Gain on Sale	[6]					$ 77,592
Disposed of by Sale, Not Discontinued Operations [Member] | 2015 Properties Sold [Member]
Real Estate [Line Items]
Number of Units | apartment							506
Rentable Square Feet Sold | ft²							197,000
Contract Sale Price							$ 137,100
Gain on Sale							$ 89,653
Disposed of by Sale, Not Discontinued Operations [Member] | 2015 Properties Sold [Member] | Multifamily [Member] | Country Club Towers [Member]
Real Estate [Line Items]
Number of Units | apartment							227
Contract Sale Price							$ 37,800
Gain on Sale							30,277
Disposed of by Sale, Not Discontinued Operations [Member] | 2015 Properties Sold [Member] | Multifamily [Member] | 1225 First Street [Member]
Real Estate [Line Items]
Contract Sale Price	[7]						14,500
Gain on Sale	[8]						$ 0
Disposed of by Sale, Not Discontinued Operations [Member] | 2015 Properties Sold [Member] | Multifamily [Member] | Munson Hill Towers [Member]
Real Estate [Line Items]
Number of Units | apartment							279
Contract Sale Price							$ 57,050
Gain on Sale							$ 51,395
Disposed of by Sale, Not Discontinued Operations [Member] | 2015 Properties Sold [Member] | Retail [Member] | Montgomery Village Center [Member]
Real Estate [Line Items]
Rentable Square Feet Sold | ft²							197,000
Contract Sale Price							$ 27,750
Gain on Sale							$ 7,981
[1]	Land held for future development and an interest in a parking garage.
[2]	Land held for future development and an interest in a parking garage.
[3]	Maryland Office Portfolio Transaction I consists of 6110 Executive Boulevard, 600 Jefferson Plaza, Wayne Plaza and West Gude Drive.
[4]	Maryland Office Portfolio Transaction I consists of 6110 Executive Boulevard, 600 Jefferson Plaza, Wayne Plaza and West Gude Drive.
[5]	Maryland Office Portfolio Transaction II consists of 51 Monroe Street and One Central Plaza.
[6]	Maryland Office Portfolio Transaction II consists of 51 Monroe Street and One Central Plaza.
[7]	Interest in land held for future development.
[8]	Interest in land held for future development.

Real Estate - Real Estate Renta

Real Estate - Real Estate Rental Revenue and Net Income from Maryland Office Portfolio (Details) - Maryland Office Portfolio [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disposal Group Income Statement Disclosures:
Real estate rental revenue	$ 0	$ 20,266	$ 32,423
Net income	$ 0	$ 9,376	$ 9,848

Real Estate - Casualty Gains (D

Real Estate - Casualty Gains (Details) - Bethesda Hill Apartments [Member] $ in Millions	3 Months Ended
	Jun. 30, 2016USD ($)
Real Estate [Line Items]
Net casualty gain recorded	$ 0.7
Insurance Recoveries	0.9
Casualty charges to write off damaged units	$ 0.2

Mortgage Notes Payable (Details

Mortgage Notes Payable (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2017USD ($)buildings	Dec. 31, 2016USD ($)
Mortgage Loans on Real Estate [Line Items]
Collateral for mortgage notes payable | buildings		1
Real estate investment property, at cost		$ 2,702,002	$ 2,685,403
Loans Payable		91,914	144,485
Mortgage notes payable, net		$ 95,141	148,540
The Army Navy Club Building [Member]
Mortgage Loans on Real Estate [Line Items]
Debt Instrument, Issuance Date	[1],[2]	Mar. 26, 2014
Effective interest rate percentage	[2],[3]	3.18%
Loans Payable	[2]	$ 0	49,618
Debt Instrument, Maturity Date	[2]	Feb. 1, 2017
Yale West [Member]
Mortgage Loans on Real Estate [Line Items]
Debt Instrument, Issuance Date	[1],[4]	Feb. 21, 2014
Effective interest rate percentage	[3],[4]	3.75%
Loans Payable	[4]	$ 46,629	47,078
Debt Instrument, Maturity Date	[4]	Jan. 31, 2022
Olney Village Center Member
Mortgage Loans on Real Estate [Line Items]
Debt Instrument, Issuance Date	[1]	Aug. 30, 2011
Effective interest rate percentage	[3]	4.94%
Loans Payable		$ 13,091	14,851
Debt Instrument, Maturity Date		Oct. 1, 2023
Kenmore Apartments [Member]
Mortgage Loans on Real Estate [Line Items]
Debt Instrument, Issuance Date	[1],[5]	Feb. 2, 2009
Effective interest rate percentage	[3],[5]	5.37%
Loans Payable	[5]	$ 32,194	32,938
Debt Instrument, Maturity Date	[5]	Sep. 1, 2018
Mortgage payable
Mortgage Loans on Real Estate [Line Items]
Debt Instrument, Unamortized Discount (Premium), Net		$ 3,385	4,354
Deferred Finance Costs, Net		158	299
First Mortgage [Member]
Mortgage Loans on Real Estate [Line Items]
Real estate investment property, at cost		$ 208,300	$ 280,400
[1]	Each of these mortgages was assumed with the acquisition of the collateralized properties, except for the mortgage note secured by Kenmore Apartments, which was originally executed by Washington REIT. We record mortgages assumed in an acquisition at fair value.
[2]	The note was prepaid without penalty in February 2017.
[3]	Yield on the assumption/issuance date, including the effects of any premiums, discounts or fair value adjustments on the notes.
[4]	The maturity date of the mortgage note is January 1, 2052, but can be prepaid, without penalty, beginning on January 31, 2022.
[5]	5) The maturity date of the mortgage note is March 1, 2019, but can be prepaid, without penalty, beginning on September 1, 2018.

Mortgage Notes Payable - Schedu

Mortgage Notes Payable - Scheduled Principal Payments (Details) $ in Thousands	Dec. 31, 2017USD ($)
Scheduled Principal Payments [Abstract]
2,018	$ 34,544
2,019	2,500
2,020	2,659
2,021	2,829
2,022	46,984
Thereafter	2,398
Total principal	$ 91,914

Unsecured Lines Of Credit Pay64

Unsecured Lines Of Credit Payable - Narrative (Details)	Jun. 23, 2015	Sep. 30, 2017	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Jul. 21, 2016	Sep. 15, 2015
Line of Credit Facility [Line Items]
Total revolving credit facilities at December 31			$ 600,000,000	$ 600,000,000	$ 600,000,000
Weighted average interest rate during the year			2.15%	1.52%	1.35%
U.S. Covered Terrorism Losses, Percent			0.85
Insurance Provider, Covered Terrorism Losses, Percent			0.10
Aggregate Insurance Limit For Terrorism Losses			$ 100,000,000,000
Line of Credit [Member]
Line of Credit Facility [Line Items]
Weighted average interest rate during the year		1.00%
Line of Credit Facility, Commitment Fee Percentage		0.20%
Credit Facility No 1 [Member]
Line of Credit Facility [Line Items]
Total revolving credit facilities at December 31			100,000,000
Credit Facility No 2 [Member]
Line of Credit Facility [Line Items]
Total revolving credit facilities at December 31			400,000,000
credit facility 2015 [Member]
Line of Credit Facility [Line Items]
Total revolving credit facilities at December 31			1,000,000,000
credit facility 2015 [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Total revolving credit facilities at December 31			$ 600,000,000
line of credit facility, number of extensions allowed			2
Line of Credit Facility, extension period			6 months
credit facility 2015 [Member] | 2015 Term Loan [Member]
Line of Credit Facility [Line Items]
Long-term Line of Credit, Noncurrent			$ 150,000,000
Debt Instrument, Term			5 years 6 months
London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Variable Rate			1.56425%
London Interbank Offered Rate (LIBOR) [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Spread on variable rate	1.00%
London Interbank Offered Rate (LIBOR) [Member] | 2015 Term Loan [Member]
Line of Credit Facility [Line Items]
Spread on variable rate			1.10%
Federal Funds Effective Swap Rate [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Spread on variable rate	0.50%
Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Derivative, Number of Instruments Held			2			2	2
Effective interest rate percentage			2.70%
Minimum [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Commitment Fee Percentage	0.125%
Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Spread on variable rate	0.875%
Minimum [Member] | Base Rate [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Spread on variable rate	0.00%
Maximum [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Commitment Fee Percentage	0.30%
Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Spread on variable rate	1.55%
Maximum [Member] | Base Rate [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Spread on variable rate	0.55%

Unsecured Lines Of Credit Pay65

Unsecured Lines Of Credit Payable - Revolving Line of Credit (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Line of Credit Facility [Line Items]
Committed capacity	$ 600,000,000	$ 600,000,000	$ 600,000,000
Borrowings outstanding	166,000,000	120,000,000	$ 105,000,000
credit facility 2015 [Member]
Line of Credit Facility [Line Items]
Committed capacity	1,000,000,000
credit facility 2015 [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Committed capacity	600,000,000
Borrowings outstanding	166,000,000	$ 120,000,000
Unused and available	$ 434,000,000

Unsecured Lines Of Credit Pay66

Unsecured Lines Of Credit Payable - Repayment of Revolving Credit Facility (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Line of Credit Facility, Amount Outstanding [Roll Forward]
Long-term Line of Credit	$ 120,000
Long-term Line of Credit	166,000
credit facility 2015 [Member] | Line of Credit [Member]
Line of Credit Facility, Amount Outstanding [Roll Forward]
Long-term Line of Credit	120,000
Proceeds from Lines of Credit	274,000
Repayments of Lines of Credit	228,000
Long-term Line of Credit	$ 166,000

Unsecured Lines Of Credit Pay67

Unsecured Lines Of Credit Payable - Recognized Interest Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Unsecured Debt [Abstract]
Line of Credit Facility, Periodic Payment, Interest	$ 3,857	$ 3,272	$ 2,266
Line of Credit Facility, Commitment Fee Amount	$ 1,217	$ 1,220	$ 1,241

Unsecured Lines Of Credit Pay68

Unsecured Lines Of Credit Payable - Revolving Credit Facility (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Unsecured Debt [Abstract]
Total revolving credit facilities at December 31	$ 600,000	$ 600,000	$ 600,000
Borrowings outstanding	166,000	120,000	105,000
Weighted average daily borrowings during the year	179,633	214,962	167,573
Maximum daily borrowings during the year	$ 252,000	$ 358,000	$ 350,000
Weighted average interest rate during the year	2.15%	1.52%	1.35%
Weighted average interest rate on borrowings outstanding at December 31	2.54%	1.64%	1.36%

Notes Payable - Unsecured Notes

Notes Payable - Unsecured Notes (Details) - USD ($)		3 Months Ended	12 Months Ended
		Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Notes Payable			$ 894,358,000	$ 843,084,000
Total principal			91,914,000
Debt Instrument, Periodic Payment, Principal			0
Proceeds from term loan			50,000,000	$ 100,000,000	$ 150,000,000
Notes payable
Debt Instrument [Line Items]
Notes Payable			894,358,000
Total principal			900,000,000
Net unamortized discount			(1,580,000)
Debt Issuance Cost			$ (4,062,000)
Notes payable | 10 Year Unsecured Notes 5.053% [Member]
Debt Instrument [Line Items]
Coupon stated rate			4.95%
Effective interest rate percentage	[1]		5.05%
Notes Payable			$ 250,000,000
Debt Instrument, Maturity Date	[2]		Oct. 1, 2020
Notes payable | 2015 Term Loan [Member]
Debt Instrument [Line Items]
Effective interest rate percentage	[1]		2.72%
Long-term Line of Credit, Noncurrent			$ 150,000,000
Debt Instrument, Maturity Date	[2]		Mar. 15, 2021
Notes payable | 10 Year Unsecured Notes 3.950 % [Member]
Debt Instrument [Line Items]
Coupon stated rate			3.95%
Effective interest rate percentage	[1]		4.02%
Notes Payable			$ 300,000,000
Debt Instrument, Maturity Date	[2]		Oct. 15, 2022
Notes payable | 2016 Term Loan [Member]
Debt Instrument [Line Items]
Effective interest rate percentage	[1]		2.86%
Long-term Line of Credit, Noncurrent			$ 150,000,000
Debt Instrument, Maturity Date	[2]		Jul. 21, 2023
Debt Instrument, Term			7 years
Debt Instrument, Face Amount			$ 150,000,000
Debt Instrument, Deferred Draw Period			6 months
Proceeds from term loan		$ 50,000,000	$ 100,000,000
Notes payable | 30 Year Unsecured Notes [Member]
Debt Instrument [Line Items]
Coupon stated rate			7.25%
Effective interest rate percentage	[1]		7.36%
Notes Payable			$ 50,000,000
Debt Instrument, Maturity Date	[2]		Feb. 25, 2028
London Interbank Offered Rate (LIBOR) [Member] | 2016 Term Loan [Member]
Debt Instrument [Line Items]
Spread on variable rate			1.00%
London Interbank Offered Rate (LIBOR) [Member] | Notes payable | 2016 Term Loan [Member]
Debt Instrument [Line Items]
Spread on variable rate			1.65%
London Interbank Offered Rate (LIBOR) [Member] | 2015 Term Loan [Member]
Debt Instrument [Line Items]
Spread on variable rate			1.10%
Federal Funds Effective Swap Rate [Member] | 2016 Term Loan [Member]
Debt Instrument [Line Items]
Spread on variable rate			0.50%
Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member] | 2016 Term Loan [Member]
Debt Instrument [Line Items]
Spread on variable rate			1.50%
Minimum [Member] | Base Rate [Member] | 2016 Term Loan [Member]
Debt Instrument [Line Items]
Spread on variable rate			0.50%
Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member] | 2016 Term Loan [Member]
Debt Instrument [Line Items]
Spread on variable rate			2.45%
Maximum [Member] | Base Rate [Member] | 2016 Term Loan [Member]
Debt Instrument [Line Items]
Spread on variable rate			1.45%
[1]	For fixed rate notes, the effective rate represents the yield on issuance date, including the effects of discounts on the notes. For variable rate notes, the effective rate represents the rate as fixed by interest rate derivatives (see note 7).
[2]	No principal amounts are due prior to maturity.

Notes Payable - Maturities of N

Notes Payable - Maturities of Notes Payable (Details) $ in Thousands	Dec. 31, 2017USD ($)
Required Principal Payments [Abstract]
2,018	$ 34,544
2,019	2,500
2,020	2,659
2,021	2,829
2,022	46,984
Thereafter	2,398
Total principal	91,914
Notes payable
Required Principal Payments [Abstract]
2,018	0
2,019	0
2,020	250,000
2,021	150,000
2,022	300,000
Thereafter	200,000
Total principal	$ 900,000

Derivative Instruments - Narrat

Derivative Instruments - Narrative (Details)		12 Months Ended
		Dec. 31, 2017USD ($)Rate	Jul. 22, 2016USD ($)	Jul. 21, 2016	Sep. 15, 2015USD ($)
Derivative [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months		$ 1,100,000
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Number of Instruments Held		2		2	2
Derivative, Notional Amount		$ 300,000,000
Effective interest rate percentage		2.70%
Fair Value Hedge Assets		$ 9,400,000
2015 Term Loan [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		$ 150,000,000			$ 150,000,000
Effective interest rate percentage | Rate		2.72%
2016 Term Loan [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		$ 150,000,000	$ 150,000,000
Effective interest rate percentage	[1]	2.86%
Debt Instrument, Maturity Date		Jul. 21, 2023
Unsecured Debt [Member] | 2015 Term Loan [Member]
Derivative [Line Items]
Effective interest rate percentage	[1]	2.72%
Debt Instrument, Maturity Date	[2]	Mar. 15, 2021
Unsecured Debt [Member] | 2016 Term Loan [Member]
Derivative [Line Items]
Effective interest rate percentage	[1]	2.86%
Debt Instrument, Maturity Date	[2]	Jul. 21, 2023
[1]	For fixed rate notes, the effective rate represents the yield on issuance date, including the effects of discounts on the notes. For variable rate notes, the effective rate represents the rate as fixed by interest rate derivatives (see note 7).
[2]	No principal amounts are due prior to maturity.

Derivative Instruments - Schedu

Derivative Instruments - Schedule of Derivatives (Details) - Interest Rate Swap [Member] - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Jul. 22, 2016	Sep. 15, 2015
Derivative [Line Items]
Derivative, Notional Amount			$ 300,000,000
Derivative Asset	$ 7,611,000		9,419,000
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	8,161,000	$ (550,000)
2015 Term Loan [Member]
Derivative [Line Items]
Derivative, Notional Amount			150,000,000		$ 150,000,000
2016 Term Loan [Member]
Derivative [Line Items]
Derivative, Notional Amount			150,000,000	$ 150,000,000
Prepaid expenses and other assets [Member]
Derivative [Line Items]
Derivative Asset	7,611,000		9,419,000
Prepaid expenses and other assets [Member] | 2015 Term Loan [Member]
Derivative [Line Items]
Derivative Asset	417,000		1,987,000
Prepaid expenses and other assets [Member] | 2016 Term Loan [Member]
Derivative [Line Items]
Derivative Asset	$ 7,194,000		$ 7,432,000

Fair Value Disclosures - Financ

Fair Value Disclosures - Financial Assets And Liabilities Measured At Fair Value (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
SERP	$ 1,858	$ 1,407
Cash and Cash Equivalents and Restricted Cash Maturity Period	90 days
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
SERP	$ 0	0
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
SERP	1,858	1,407
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
SERP	0	0
Interest Rate Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	9,419	7,611
Interest Rate Swap [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	0	0
Interest Rate Swap [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	9,419	7,611
Interest Rate Swap [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	$ 0	$ 0

Fair Value Disclosures - Fina74

Fair Value Disclosures - Financial Assets And Liabilities Not Measured At Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 9,847	$ 11,305	$ 23,825
Restricted cash	2,776	6,317	$ 13,383
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage notes payable	95,141	148,540
Lines of credit payable	166,000	120,000
Notes payable	894,358	843,084
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	9,847	11,305
Restricted cash	2,776	6,317
Mortgage notes payable	97,181	149,997
Lines of credit payable	166,000	120,000
Notes payable	931,377	873,516
2445 M Street [Member] | Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
2445 M Street note receivable	0	2,089
2445 M Street [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
2445 M Street note receivable	$ 0	$ 2,173

Stock Based Compensation - Narr

Stock Based Compensation - Narrative (Details)	12 Months Ended
	Dec. 31, 2017shares
Washington Real Estate Investment Trust 2016 Omnibus Long Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized	2,400,000
Plan in effect, period	10 years
Options outstanding	0
Washington Real Estate Investment Trust 2007 Omnibus Long Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized	2,000,000

Stock Based Compensation - Shor

Stock Based Compensation - Short Term and Long-Term Incentive Plan Narrative (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation cost not yet recognized, period for recognition	35 months
One-time equity award granted (shares)	330,639	251,694	251,642
Restricted Share Awards [Member] | Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
One-time equity award granted (shares)	100,000
Percentage of equity award that vests on fifth anniversary of grant date	100.00%
New STIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period	1 year
Percentage of Potential Award Based Upon Service Requirement	50.00%
Share-based Compensation Arrangements by Share-based Payment Awards, Options, Vested after Performance Period, Percentage	50.00%
New STIP [Member] | Performance-Based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
New LTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage payable In unrestricted shares	75.00%
Percentage payable in restricted shares	25.00%
Performance period	3 years
Award vesting period	3 years
Grant Date Fair Value as a Percentage of Base Salary on absolute TSR	50.00%	50.00%	50.00%
Grant Date Fair Value as a Percentage of Base Salary on relative TSR	50.00%	50.00%	50.00%
Total compensation cost not yet recognized, period for recognition	4 years
Weighting for performance measurement based on cumulative 3-Year total shareholder return	50.00%
Weighting for performance measurement based on select peer comapnies	0.50
New LTIP [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant Date Fair Value as a Percentage of Base Salary on absolute TSR	13.00%	17.00%	13.00%
Grant Date Fair Value as a Percentage of Base Salary on relative TSR	37.00%	38.00%	40.00%
Grant date fair value as a percentage of base salary	80.00%
New LTIP [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant Date Fair Value as a Percentage of Base Salary on absolute TSR	31.00%	30.00%	29.00%
Grant Date Fair Value as a Percentage of Base Salary on relative TSR	67.00%	66.00%	69.00%
Grant date fair value as a percentage of base salary	150.00%
Cash [Member] | New STIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage payable In unrestricted shares	100.00%
Cash [Member] | New STIP [Member] | Performance-Based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage payable In unrestricted shares	50.00%
Restricted Share Units [Member] | New STIP [Member] | Performance-Based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage payable in restricted shares	50.00%
Restricted Share Units [Member] | New LTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period	1 year
Restricted Share Units [Member] | New LTIP [Member] | Performance-Based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation cost not yet recognized, period for recognition	4 years
Unrestricted Share Awards [Member] | New LTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation cost not yet recognized, period for recognition	3 years

Stock Based Compensation - Assu

Stock Based Compensation - Assumptions for LTIP Awards (Details) - New LTIP [Member] - $ / shares		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected Volatility Rate	[1]		18.20%
Risk Free Interest Rate	[2]	1.50%	1.30%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Exercise Price	[2]		$ 27.060
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected Volatility Rate	[1]	0.00%		0.00%
Risk Free Interest Rate	[2]			0.00%
Expected Term	[3]	3 years	3 years	3 years
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Exercise Price		$ 30.84		$ 27.66
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected Volatility Rate	[1]	18.70%		17.50%
Risk Free Interest Rate	[2]			0.00%
Expected Term	[3]	4 years	4 years	4 years
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Exercise Price		$ 32.69		$ 27.76
[1]	Expected volatility based upon historical volatility of our daily closing share price.
[2]	Risk-free interest rate based on U.S. treasury constant maturity bonds on the measurement date with a maturity equal to the market condition performance period.
[3]	Expected term based on the market condition performance period.

Stock Based Compensation - Trus

Stock Based Compensation - Trustee Awards and Total Compensation Expense Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	$ 4,800,000	$ 3,500,000	$ 5,100,000
Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Capitalized Amount	200,000	100,000	600,000
Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred Compensation Arrangement with Individual, Fair Value of Shares Issued	$ 100,000	$ 100,000	$ 100,000

Stock Based Compensation - Rest

Stock Based Compensation - Restricted Share Awards with Performance and Service Conditions (Details) - Restricted Share Awards [Member] - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Other Than Options, Nonvested, Number, Beginning	107,699	106,144	93,667
Other Than Options, Granted	330,639	251,694	251,642
Other Than Options, Vested During Year	(194,569)	(211,771)	(212,856)
Other Than Options, Forfeited	(7,075)	(38,368)	(26,309)
Other Than Options, Nonvested, Number, Beginning	236,694	107,699	106,144
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Other Than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 26.47	$ 27.71	$ 25.22
Other Than Options, Granted, Weighted Average Grant Date Fair Value	32.46	26.01	27.80
Other Than Options, Vested During Year, Weighted Average Grant Date Fair Value	30.50	29.21	27.18
Other Than Options, Forfeited, Weighted Average Grant Date Fair Value	27.43	26.14	26.77
Other Than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 27.96	$ 26.47	$ 27.71

Stock Based Compensation - Re80

Stock Based Compensation - Restricted Share Awards with Performance and Service Conditions Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of restricted share units vested	$ 5.9	$ 6.2	$ 5.8
Restricted Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 6.6
Total compensation cost not yet recognized, period for recognition	35 months

Stock Based Compensation - Re81

Stock Based Compensation - Restricted and Unrestricted Shares with Market Conditions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Relative TSR [Member] | Restricted Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted and Unrestricted Share Awards, Grant Date Fair Value	$ 222	$ 182	$ 191
Unamortized Value Of Restricted and Unrestricted Shares	166	117	83
Relative TSR [Member] | Unrestricted Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted and Unrestricted Share Awards, Grant Date Fair Value	666	546	634
Unamortized Value Of Restricted and Unrestricted Shares	444	314	165
Absolute TSR [Member] | Restricted Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted and Unrestricted Share Awards, Grant Date Fair Value	100	82	76
Unamortized Value Of Restricted and Unrestricted Shares	75	53	33
Absolute TSR [Member] | Unrestricted Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted and Unrestricted Share Awards, Grant Date Fair Value	299	246	254
Unamortized Value Of Restricted and Unrestricted Shares	$ 199	$ 142	$ 66

Other Benefit Plans - Narrative

Other Benefit Plans - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
401I(k) plan contributions by employer	$ 0.4	$ 0.4	$ 0.5
Liability, Other Postretirement Defined Benefit Plan, Noncurrent	1	0.9
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	0.3	0.2	$ 0.3
Officer [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Accrued benefit liability	$ 1.8	$ 1.3

Earnings Per Common Share - Com

Earnings Per Common Share - Computation Of Basic And Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net income	$ 2,337		$ 2,813		$ 7,847		$ 6,615		$ 5,426		$ 79,662		$ 31,821		$ 2,379		$ 19,612	$ 119,288	$ 89,187
Net loss attributable to noncontrolling interests																	56	51	553
Allocation of undistributed earnings to unvested restricted share awards and units to continuing operations																	(362)	(310)	(269)
Adjusted net income attributable to the controlling interests																	$ 19,306	$ 119,029	$ 89,471
Denominator:
Weighted average shares outstanding – basic (in shares)																	76,820	72,163	68,177
Effect of dilutive securities:
Operating partnership units																	9	0	0
Employee stock options and restricted share awards																	106	176	133
Weighted average shares outstanding – diluted (in shares)																	(76,935)	(72,339)	(68,310)
Basic net income attributable to the controlling interests per share (in dollars per share)	$ 0.03	[1]	$ 0.04	[1],[2]	$ 0.10	[1],[2]	$ 0.09	[1]	$ 0.07	[1],[2]	$ 1.07	[1]	$ 0.44	[1],[2]	$ 0.03	[1],[2]	$ 0.25	$ 1.65	$ 1.31
Diluted net income attributable to the controlling interests per share (in dollars per share)	$ 0.03	[1]	$ 0.04	[1],[2]	$ 0.10	[1],[2]	$ 0.09	[1]	$ 0.07	[1],[2]	$ 1.07	[1]	$ 0.44	[1],[2]	$ 0.03	[1],[2]	0.25	1.65	1.31
Dividends declared per common share (in dollars per share)																	$ 1.20	$ 1.20	$ 1.20
[1]	With regard to per share calculations, the sum of the quarterly results may not equal full year results due to rounding.
[2]	The fourth quarter of 2017 includes gain on sale of real estate classified as continuing operations of $24.9 million. The second and third quarters of 2016 include gains on sale of real estate classified as continuing operations of $24.1 million and $77.6 million, respectively.

Rentals Under Operating Lease84

Rentals Under Operating Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Leases, Operating [Abstract]
2,018	$ 190,391
2,019	172,289
2,020	157,694
2,021	132,150
2,022	109,713
Thereafter	376,904
Operating Leases, Future Minimum Payments Receivable	1,139,141
Operating Leased Assets [Line Items]
Tenant Reimbursements	$ 35,400	$ 35,200	$ 34,600
Multifamily Properties [Member]
Operating Leased Assets [Line Items]
Lessee, Operating Lease, Term of Contract	1 year

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Development Contracts with Third Parties, Number	0

Segment Information - Financial

Segment Information - Financial Information by Segment (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2017USD ($)segment	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment									3
Segment Reconciliation [Abstract]
Real estate rental revenue	$ 81,302	$ 82,819	$ 83,456	$ 77,501	$ 76,952	$ 79,770	$ 79,405	$ 77,137	$ 325,078	$ 313,264	$ 306,427
Real estate expenses									115,650	115,013	112,234
Net operating income									209,428	198,251	194,193
Depreciation and amortization									(112,056)	(108,406)	(108,935)
General and administrative									(22,580)	(19,545)	(20,123)
Casualty gain									(33,152)	676	(5,909)
Acquisition costs									0	(1,178)	(2,056)
Interest expense									(47,534)	(53,126)	(59,546)
Other income									507	297	709
Gain on sale of real estate	24,900					77,600	24,100		24,915	101,704	91,107
Income tax benefit (expense)									84	615	(134)
Loss on extinguishment of debt									0	0	(119)
Net income	2,337	2,813	7,847	6,615	5,426	79,662	31,821	2,379	19,612	119,288	89,187
Less: Net loss attributable to noncontrolling interests in subsidiaries									(56)	(51)	(553)
Net income attributable to the controlling interests	2,337	$ 2,833	$ 7,864	$ 6,634	5,445	$ 79,674	$ 31,836	$ 2,384	19,668	119,339	89,740
Capital expenditures									64,381	58,014	43,636
Total assets	2,359,426				2,253,619				$ 2,359,426	$ 2,253,619	$ 2,191,168
Office [Member]
Segment Reporting Information [Line Items]
Real estate rental revenue as a percentage of total									0.52	0.53	0.57
Percentage of total income producing real estate assets									0.50	0.50
Segment Reconciliation [Abstract]
Real estate rental revenue									$ 167,438	$ 165,934	$ 174,378
Real estate expenses									62,824	64,405	67,228
Net operating income									104,614	101,529	107,150
Capital expenditures									30,407	30,337	29,745
Total assets	1,203,187				1,104,589				$ 1,203,187	$ 1,104,589	$ 1,265,570
Retail [Member]
Segment Reporting Information [Line Items]
Real estate rental revenue as a percentage of total									0.19	0.20	0.21
Percentage of total income producing real estate assets									0.17	0.17
Segment Reconciliation [Abstract]
Real estate rental revenue									$ 62,390	$ 61,566	$ 63,507
Real estate expenses									15,186	15,860	15,606
Net operating income									47,204	45,706	47,901
Capital expenditures									2,128	8,821	3,897
Total assets	346,580				352,056				$ 346,580	$ 352,056	$ 354,123
Multifamily [Member]
Segment Reporting Information [Line Items]
Real estate rental revenue as a percentage of total									0.29	0.27	0.22
Percentage of total income producing real estate assets									0.33	0.33
Segment Reconciliation [Abstract]
Real estate rental revenue									$ 95,250	$ 85,764	$ 68,542
Real estate expenses									37,640	34,748	29,400
Net operating income									57,610	51,016	39,142
Capital expenditures									27,980	17,936	7,865
Total assets	767,279				762,695				767,279	762,695	529,773
Corporate And Other [Member]
Segment Reconciliation [Abstract]
Real estate rental revenue									0	0	0
Real estate expenses									0	0	0
Net operating income									0	0	0
Capital expenditures									3,866	920	2,129
Total assets	$ 42,380				$ 34,279				$ 42,380	$ 34,279	$ 41,702

Selected Quarterly Financial 87

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Real estate rental revenue	$ 81,302		$ 82,819		$ 83,456		$ 77,501		$ 76,952		$ 79,770		$ 79,405		$ 77,137		$ 325,078	$ 313,264	$ 306,427
Net income	2,337		2,813		7,847		6,615		5,426		79,662		31,821		2,379		19,612	119,288	89,187
Net income attributable to the controlling interests	$ 2,337		$ 2,833		$ 7,864		$ 6,634		$ 5,445		$ 79,674		$ 31,836		$ 2,384		$ 19,668	$ 119,339	$ 89,740
Net income per share - Basic (in dollars per share)	$ 0.03	[1]	$ 0.04	[1],[2]	$ 0.10	[1],[2]	$ 0.09	[1]	$ 0.07	[1],[2]	$ 1.07	[1]	$ 0.44	[1],[2]	$ 0.03	[1],[2]	$ 0.25	$ 1.65	$ 1.31
Net income per share - Diluted (in dollars per share)	$ 0.03	[1]	$ 0.04	[1],[2]	$ 0.10	[1],[2]	$ 0.09	[1]	$ 0.07	[1],[2]	$ 1.07	[1]	$ 0.44	[1],[2]	$ 0.03	[1],[2]	$ 0.25	$ 1.65	$ 1.31
Gain on sale of real estate	$ 24,900										$ 77,600		$ 24,100				$ 24,915	$ 101,704	$ 91,107
Impairment of real estate	$ 28,152		$ 5,000
[1]	With regard to per share calculations, the sum of the quarterly results may not equal full year results due to rounding.
[2]	The fourth quarter of 2017 includes gain on sale of real estate classified as continuing operations of $24.9 million. The second and third quarters of 2016 include gains on sale of real estate classified as continuing operations of $24.1 million and $77.6 million, respectively.

Shareholders' Equity - Narrativ

Shareholders' Equity - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jun. 30, 2015
Class of Stock [Line Items]
Net proceeds from equity offerings		$ 113,194,000	$ 172,936,000	$ 5,215,000
Common stock reserved for future issuance					$ 200,000,000
Shares issued During Period, Value, Dividend Reinvestment Program		$ 2,576,000	$ 700,000
Common Stock [Member]
Class of Stock [Line Items]
Stock issued during period (in shares)	5,300,000	3,587,000	6,223,000	184,000
Pursuant of underwriter over-allotment (in shares)	693,750
Shares issued (in dollars per share)	$ 28.20
Net proceeds from equity offerings	$ 143,400,000
Shares issued under Dividend Reinvestment Program (in shares)		80,000	23,000
Stock issued during period, weighted share price, dividend reinstated plan (in dollars per share)		$ 32.25	$ 30.98
Shares issued During Period, Value, Dividend Reinvestment Program		$ 1,000
Additional Paid In Capital [Member]
Class of Stock [Line Items]
Shares issued During Period, Value, Dividend Reinvestment Program		$ 2,575,000	$ 700,000
2016 Equity Distribution Agreements [Member] | Common Stock [Member]
Class of Stock [Line Items]
Stock issued during period (in shares)		3,600,000	900,000
Net proceeds from equity offerings		$ 113,200,000	$ 29,600,000
Stock issued during period, weighted average price (in dollars per share)		$ 32.06	$ 33.32
2012 BNY Mellon Capital financing agreement [Member] | Common Stock [Member]
Class of Stock [Line Items]
Stock issued during period (in shares)				200,000
Net proceeds from equity offerings				$ 5,200,000
Stock issued during period, weighted average price (in dollars per share)				$ 28.34

Deferred Costs - Deferred Lease

Deferred Costs - Deferred Lease Costs and Incentives in Prepaid Expenses and Other Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deferred Costs, Leasing, Gross	$ 68,213	$ 58,391
Deferred Costs, Leasing, Accumulated Amortization	28,523	22,748
Deferred Costs, Leasing, Net	39,690	35,643
Deferred Leasing Incentives, Gross	24,946	21,157
Accumulated Amortization, Deferred Leasing Incentives	11,114	8,061
Deferred Leasing Incentives, Net	$ 13,832	$ 13,096

Deferred Costs - Amortization a

Deferred Costs - Amortization and Write-Offs of Deferred Leasing Costs and Incentives (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deferred leasing costs amortization	$ 6,418	$ 6,076	$ 5,983
Deferred leasing incentives amortization	$ 3,163	$ 2,994	$ 2,848

Subsequent Event - Narrative (D

Subsequent Event - Narrative (Details) $ in Thousands		Jan. 18, 2018USD ($)ft²	Dec. 31, 2017USD ($)ft²	Dec. 31, 2016USD ($)
Subsequent Event [Line Items]
Net Rentable Area | ft²	[1]		9,948,000
Real estate investment property, at cost | $			$ 2,702,002	$ 2,685,403
Arlington Tower [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Net Rentable Area | ft²		398,000
Real estate investment property, at cost | $		$ 250,000
[1]	As of December 31, 2017, Washington REIT had under development multifamily properties, the Wellington land parcel (Trove) and Riverside Apartments land parcel. The value not yet placed into service at December 31, 2017 was $29.7 million and $19.2 million, respectively.

Schedule II (Details)

Schedule II (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for doubtful accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 2,377	$ 2,297	$ 3,392
Additions Charged to Expenses	882	1,706	1,368
Net Deductions (Recoveries)	(833)	(1,626)	(2,463)
Balance at End of Year	2,426	2,377	2,297
Valuation allowance for deferred tax assets
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	2,882	5,705	5,714
Additions Charged to Expenses	0	0	0
Net Deductions (Recoveries)	$ (1,469)	(2,823)	(9)
Balance at End of Year		$ 2,882	$ 5,705

Schedule III (Details)

Schedule III (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2017USD ($)unit		Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2017USD ($)ft²		Apr. 04, 2017ft²	Dec. 31, 2016USD ($)
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost, Land	[1]					$ 645,303
Initial Cost, Buildings and Improvements	[1]					1,580,095
Net Improvements (Retirement) since Acquisition						606,285
Gross Amounts at Which Carried at December 31, 2016, Land						604,640
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						2,227,043
Gross Amounts at Which Carried at December 31, 2016, Total		$ 2,725,635		$ 2,673,891	$ 2,547,188	2,831,683	[2]		$ 2,725,635
Accumulated Depreciation at December 31, 2016		$ 657,425		692,608	640,434	$ 690,417			657,425
Net Rentable Area | ft²	[3]					9,948,000
Units | unit		4,268
Loans Payable						$ 91,914			144,485
Real estate, federal income tax basis						1,983,300
Properties under development or held for future development						54,422			40,232
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, beginning of period		$ 2,725,635		2,673,891	2,547,188
Property acquisitions	[4]	124,306		240,499	162,702
Improvements	[4]	84,560		66,840	50,954
Impairment write-down		(81,982)		0	(5,909)
Write-off of disposed assets		(2,655)		(1,272)	(3,291)
Property sales		(18,181)		(254,323)	(77,753)
Balance, end of period		2,831,683	[2]	2,725,635	2,673,891
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, beginning of period		657,425		692,608	640,434
Depreciation		94,558		88,347	86,536
SEC Schedule III, Real Estate Accumulated Depreciation, Other Deductions		48,830		0	0
Write-off of disposed assets		(1,708)		(486)	(2,408)
Property sales		(11,028)		(123,044)	(31,954)
Balance, end of period		$ 690,417		$ 657,425	$ 692,608
Minimum [Member]
Real Estate and Accumulated Depreciation [Line Items]
Useful Life		3 years
Maximum [Member]
Real Estate and Accumulated Depreciation [Line Items]
Useful Life		50 years
Multifamily Properties [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost, Land						177,130
Initial Cost, Buildings and Improvements						473,916
Net Improvements (Retirement) since Acquisition						294,381
Gross Amounts at Which Carried at December 31, 2016, Land						148,569
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						796,858
Gross Amounts at Which Carried at December 31, 2016, Total		$ 945,427				945,427
Accumulated Depreciation at December 31, 2016		185,882				$ 185,882
Net Rentable Area | ft²						3,594,000
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period		945,427
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 185,882
3801 Connecticut [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Washington, DC
Initial Cost, Land	[1]					$ 420
Initial Cost, Buildings and Improvements	[1]					2,678
Net Improvements (Retirement) since Acquisition						16,263
Gross Amounts at Which Carried at December 31, 2016, Land						420
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						18,941
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 19,361				19,361
Accumulated Depreciation at December 31, 2016		$ 11,526				$ 11,526
Year of Construction		Jan. 1, 1951
Date of Acquisition		Jan. 1, 1963
Net Rentable Area | ft²	[3]					178,000
Units | unit		307
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 19,361
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 11,526
Roosevelt Towers [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					$ 336
Initial Cost, Buildings and Improvements	[1]					1,996
Net Improvements (Retirement) since Acquisition						12,890
Gross Amounts at Which Carried at December 31, 2016, Land						336
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						14,886
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 15,222				15,222
Accumulated Depreciation at December 31, 2016		$ 10,151				$ 10,151
Year of Construction		Jan. 1, 1964
Date of Acquisition		May 1, 1965
Net Rentable Area | ft²	[3]					170,000
Units | unit		191
Depreciation Life	[5]	40 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 15,222
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 10,151
Park Adams [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					$ 287
Initial Cost, Buildings and Improvements	[1]					1,654
Net Improvements (Retirement) since Acquisition						12,935
Gross Amounts at Which Carried at December 31, 2016, Land						287
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						14,589
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 14,876				14,876
Accumulated Depreciation at December 31, 2016		$ 9,968				$ 9,968
Year of Construction		Jan. 1, 1959
Date of Acquisition		Jan. 1, 1969
Net Rentable Area | ft²	[3]					173,000
Units | unit		200
Depreciation Life	[5]	35 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 14,876
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 9,968
The Ashby at McLean [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					$ 4,356
Initial Cost, Buildings and Improvements	[1]					17,102
Net Improvements (Retirement) since Acquisition						23,569
Gross Amounts at Which Carried at December 31, 2016, Land						4,356
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						40,671
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 45,027				45,027
Accumulated Depreciation at December 31, 2016		$ 25,312				$ 25,312
Year of Construction		Jan. 1, 1982
Date of Acquisition		Aug. 1, 1996
Net Rentable Area | ft²	[3]					274,000
Units | unit		256
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 45,027
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 25,312
Bethesda Hill Apartments [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Maryland
Initial Cost, Land	[1]					$ 3,900
Initial Cost, Buildings and Improvements	[1]					13,412
Net Improvements (Retirement) since Acquisition						13,896
Gross Amounts at Which Carried at December 31, 2016, Land						3,900
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						27,308
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 31,208				31,208
Accumulated Depreciation at December 31, 2016		$ 18,904				$ 18,904
Year of Construction		Jan. 1, 1986
Date of Acquisition		Nov. 1, 1997
Net Rentable Area | ft²	[3]					225,000
Units | unit		195
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 31,208
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 18,904
Bennett Park [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					$ 2,861
Initial Cost, Buildings and Improvements	[1]					917
Net Improvements (Retirement) since Acquisition						80,278
Gross Amounts at Which Carried at December 31, 2016, Land						4,774
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						79,282
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 84,056				84,056
Accumulated Depreciation at December 31, 2016		$ 34,586				$ 34,586
Year of Construction		Jan. 1, 2007
Date of Acquisition		Feb. 1, 2001
Net Rentable Area | ft²	[3]					215,000
Units | unit		224
Depreciation Life	[5]	28 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 84,056
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 34,586
The Clayborne [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					$ 269
Initial Cost, Buildings and Improvements	[1]					0
Net Improvements (Retirement) since Acquisition						31,041
Gross Amounts at Which Carried at December 31, 2016, Land						699
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						30,611
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 31,310				31,310
Accumulated Depreciation at December 31, 2016		$ 15,050				$ 15,050
Year of Construction		Jan. 1, 2008
Date of Acquisition		Jun. 1, 2003
Net Rentable Area | ft²	[3]					60,000
Units | unit		74
Depreciation Life	[5]	26 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 31,310
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 15,050
The Kenmore [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Washington, DC
Initial Cost, Land	[1],[6]					$ 28,222
Initial Cost, Buildings and Improvements	[1],[6]					33,955
Net Improvements (Retirement) since Acquisition	[6]					13,694
Gross Amounts at Which Carried at December 31, 2016, Land	[6]					28,222
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements	[6]					47,649
Gross Amounts at Which Carried at December 31, 2016, Total	[2],[6]	$ 75,871				75,871
Accumulated Depreciation at December 31, 2016	[6]	$ 13,973				$ 13,973
Year of Construction		Jan. 1, 1948
Date of Acquisition	[6]	Sep. 1, 2008
Net Rentable Area | ft²	[3]					268,000
Units | unit		374
Depreciation Life	[5]	30 years
Loans Payable						$ 32,200
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2],[6]	$ 75,871
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period	[6]	$ 13,973
The Maxwell [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					12,787
Initial Cost, Buildings and Improvements	[1]					0
Net Improvements (Retirement) since Acquisition						38,035
Gross Amounts at Which Carried at December 31, 2016, Land						12,851
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						37,971
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 50,822				50,822
Accumulated Depreciation at December 31, 2016		$ 6,811				$ 6,811
Year of Construction		Jan. 1, 2014
Date of Acquisition		Jun. 1, 2011
Net Rentable Area | ft²	[3]					116,000
Units | unit		163
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 50,822
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 6,811
The Paramount [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					$ 8,568
Initial Cost, Buildings and Improvements	[1]					38,716
Net Improvements (Retirement) since Acquisition						2,345
Gross Amounts at Which Carried at December 31, 2016, Land						8,568
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						41,061
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 49,629				49,629
Accumulated Depreciation at December 31, 2016		$ 7,715				$ 7,715
Year of Construction		Jan. 1, 1984
Date of Acquisition		Oct. 1, 2013
Net Rentable Area | ft²	[3]					141,000
Units | unit		135
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 49,629
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 7,715
Yale West [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Washington, DC
Initial Cost, Land	[1],[6]					$ 14,684
Initial Cost, Buildings and Improvements	[1],[6]					62,069
Net Improvements (Retirement) since Acquisition	[6]					786
Gross Amounts at Which Carried at December 31, 2016, Land	[6]					14,684
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements	[6]					62,855
Gross Amounts at Which Carried at December 31, 2016, Total	[2],[6]	$ 77,539				77,539
Accumulated Depreciation at December 31, 2016	[6]	$ 8,808				$ 8,808
Year of Construction		Jan. 1, 2011
Date of Acquisition	[6]	Feb. 1, 2014
Net Rentable Area | ft²	[3]					173,000
Units | unit		216
Depreciation Life	[5]	30 years
Loans Payable	[7]					$ 46,629			47,078
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2],[6]	$ 77,539
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period	[6]	$ 8,808
The Wellington [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					30,548
Initial Cost, Buildings and Improvements	[1]					116,563
Net Improvements (Retirement) since Acquisition						10,161
Gross Amounts at Which Carried at December 31, 2016, Land						30,548
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						126,724
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 157,272				157,272
Accumulated Depreciation at December 31, 2016		$ 11,206				11,206
Year of Construction		Jan. 1, 1960
Date of Acquisition		Jul. 1, 2015
Units | unit		711
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 157,272
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 11,206
The Wellington land parcel [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1],[8]					15,000
Initial Cost, Buildings and Improvements	[1],[8]					0
Net Improvements (Retirement) since Acquisition	[8]					14,690
Gross Amounts at Which Carried at December 31, 2016, Land						0
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements	[8]					29,690
Gross Amounts at Which Carried at December 31, 2016, Total	[2],[8]	$ 29,690				29,690
Accumulated Depreciation at December 31, 2016		$ 0				0
Date of Acquisition		Jul. 1, 2015
Properties under development or held for future development									29,700
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2],[8]	$ 29,690
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 0
Riverside Apartments [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					38,924
Initial Cost, Buildings and Improvements	[1]					184,854
Net Improvements (Retirement) since Acquisition						20,544
Gross Amounts at Which Carried at December 31, 2016, Land						38,924
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						205,398
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 244,322				244,322
Accumulated Depreciation at December 31, 2016		$ 11,872				11,872
Year of Construction		Jan. 1, 1971
Date of Acquisition		May 20, 2016
Units | unit		1,222
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 244,322
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 11,872
Riverside Apartments land parcel [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1],[8]					15,968
Initial Cost, Buildings and Improvements	[1]					0
Net Improvements (Retirement) since Acquisition	[8]					3,254
Gross Amounts at Which Carried at December 31, 2016, Land						0
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements	[8]					19,222
Gross Amounts at Which Carried at December 31, 2016, Total	[2],[8]	$ 19,222				19,222
Accumulated Depreciation at December 31, 2016		$ 0				0
Date of Acquisition		May 20, 2016
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2],[8]	$ 19,222
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		0
Office Buildings [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost, Land						347,204
Initial Cost, Buildings and Improvements						856,681
Net Improvements (Retirement) since Acquisition						227,087
Gross Amounts at Which Carried at December 31, 2016, Land						335,449
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						1,095,523
Gross Amounts at Which Carried at December 31, 2016, Total		1,430,972				1,430,972
Accumulated Depreciation at December 31, 2016		366,155				$ 366,155
Net Rentable Area | ft²						4,021,000
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period		1,430,972
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 366,155
1901 Pennsylvania Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Washington, DC
Initial Cost, Land	[1]					$ 892
Initial Cost, Buildings and Improvements	[1]					3,481
Net Improvements (Retirement) since Acquisition						19,565
Gross Amounts at Which Carried at December 31, 2016, Land						892
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						23,046
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 23,938				23,938
Accumulated Depreciation at December 31, 2016		$ 17,042				$ 17,042
Year of Construction		Jan. 1, 1960
Date of Acquisition		May 1, 1977
Net Rentable Area | ft²						100,000
Depreciation Life	[5]	28 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 23,938
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 17,042
515 King Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					$ 4,102
Initial Cost, Buildings and Improvements	[1]					3,931
Net Improvements (Retirement) since Acquisition						8,158
Gross Amounts at Which Carried at December 31, 2016, Land						4,102
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						12,089
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 16,191				16,191
Accumulated Depreciation at December 31, 2016		$ 6,255				$ 6,255
Year of Construction		Jan. 1, 1966
Date of Acquisition		Jul. 1, 1992
Net Rentable Area | ft²						75,000
Depreciation Life	[5]	50 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 16,191
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 6,255
1220 19th Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Washington, DC
Initial Cost, Land	[1]					$ 7,803
Initial Cost, Buildings and Improvements	[1]					11,366
Net Improvements (Retirement) since Acquisition						16,550
Gross Amounts at Which Carried at December 31, 2016, Land						7,803
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						27,916
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 35,719				35,719
Accumulated Depreciation at December 31, 2016		$ 16,773				$ 16,773
Year of Construction		Jan. 1, 1976
Date of Acquisition		Nov. 1, 1995
Net Rentable Area | ft²						105,000
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 35,719
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 16,773
1600 Wilson Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					$ 6,661
Initial Cost, Buildings and Improvements	[1]					16,742
Net Improvements (Retirement) since Acquisition						28,677
Gross Amounts at Which Carried at December 31, 2016, Land						6,661
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						45,419
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 52,080				52,080
Accumulated Depreciation at December 31, 2016		$ 25,295				$ 25,295
Year of Construction		Jan. 1, 1973
Date of Acquisition		Oct. 1, 1997
Net Rentable Area | ft²						170,000
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 52,080
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 25,295
Silverline Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					$ 12,049
Initial Cost, Buildings and Improvements	[1]					71,825
Net Improvements (Retirement) since Acquisition						100,170
Gross Amounts at Which Carried at December 31, 2016, Land						12,049
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						171,995
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 184,044				184,044
Accumulated Depreciation at December 31, 2016		$ 86,729				$ 86,729
Year of Construction		Jan. 1, 1972
Date of Acquisition		Nov. 1, 1997
Net Rentable Area | ft²						549,000
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 184,044
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 86,729
Courthouse Square [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					$ 0
Initial Cost, Buildings and Improvements	[1]					17,096
Net Improvements (Retirement) since Acquisition						9,448
Gross Amounts at Which Carried at December 31, 2016, Land						0
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						26,544
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 26,544				26,544
Accumulated Depreciation at December 31, 2016		$ 15,441				$ 15,441
Year of Construction		Jan. 1, 1979
Date of Acquisition		Oct. 1, 2000
Net Rentable Area | ft²						118,000
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 26,544
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 15,441
1776 G Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Washington, DC
Initial Cost, Land	[1]					$ 31,500
Initial Cost, Buildings and Improvements	[1]					54,327
Net Improvements (Retirement) since Acquisition						9,309
Gross Amounts at Which Carried at December 31, 2016, Land						31,500
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						63,636
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 95,136				95,136
Accumulated Depreciation at December 31, 2016		$ 32,083				$ 32,083
Year of Construction		Jan. 1, 1979
Date of Acquisition		Aug. 1, 2003
Net Rentable Area | ft²						264,000
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 95,136
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 32,083
Monument II [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					$ 10,244
Initial Cost, Buildings and Improvements	[1]					65,205
Net Improvements (Retirement) since Acquisition						9,778
Gross Amounts at Which Carried at December 31, 2016, Land						10,244
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						74,983
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 85,227				85,227
Accumulated Depreciation at December 31, 2016		$ 28,830				$ 28,830
Year of Construction		Jan. 1, 2000
Date of Acquisition		Mar. 1, 2007
Net Rentable Area | ft²						208,000
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 85,227
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 28,830
2000 M Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Washington, DC
Initial Cost, Land	[1]					$ 0
Initial Cost, Buildings and Improvements	[1]					61,101
Net Improvements (Retirement) since Acquisition						22,375
Gross Amounts at Which Carried at December 31, 2016, Land						0
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						83,476
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 83,476				83,476
Accumulated Depreciation at December 31, 2016		$ 31,355				$ 31,355
Year of Construction		Jan. 1, 1971
Date of Acquisition		Dec. 1, 2007
Net Rentable Area | ft²						233,000
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 83,476
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 31,355
2445 M Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Washington, DC
Initial Cost, Land	[1]					$ 46,887
Initial Cost, Buildings and Improvements	[1]					106,743
Net Improvements (Retirement) since Acquisition						(49,374)
Gross Amounts at Which Carried at December 31, 2016, Land						37,333
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						66,923
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 104,256				104,256
Accumulated Depreciation at December 31, 2016		$ 9,099				9,099
Year of Construction		Jan. 1, 1986
Date of Acquisition		Dec. 1, 2008
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 104,256
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 9,099
925 Corporate Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					4,518
Initial Cost, Buildings and Improvements	[1]					24,801
Net Improvements (Retirement) since Acquisition						1,333
Gross Amounts at Which Carried at December 31, 2016, Land						4,518
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						26,134
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 30,652				30,652
Accumulated Depreciation at December 31, 2016		$ 9,747				$ 9,747
Year of Construction		Jan. 1, 2007
Date of Acquisition		Jun. 1, 2010
Net Rentable Area | ft²						135,000
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 30,652
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 9,747
1000 Corporate Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					$ 4,897
Initial Cost, Buildings and Improvements	[1]					25,376
Net Improvements (Retirement) since Acquisition						(186)
Gross Amounts at Which Carried at December 31, 2016, Land						4,898
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						25,189
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 30,087				30,087
Accumulated Depreciation at December 31, 2016		$ 8,978				$ 8,978
Year of Construction		Jan. 1, 2009
Date of Acquisition		Jun. 1, 2010
Net Rentable Area | ft²						136,000
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 30,087
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 8,978
1140 Connecticut Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Washington, DC
Initial Cost, Land	[1]					$ 25,226
Initial Cost, Buildings and Improvements	[1]					50,495
Net Improvements (Retirement) since Acquisition						15,987
Gross Amounts at Which Carried at December 31, 2016, Land						25,226
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						66,482
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 91,708				91,708
Accumulated Depreciation at December 31, 2016		$ 18,774				$ 18,774
Year of Construction		Jan. 1, 1966
Date of Acquisition		Jan. 1, 2011
Net Rentable Area | ft²						184,000
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 91,708
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 18,774
1227 25th Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Washington, DC
Initial Cost, Land	[1]					$ 17,505
Initial Cost, Buildings and Improvements	[1]					21,319
Net Improvements (Retirement) since Acquisition						8,653
Gross Amounts at Which Carried at December 31, 2016, Land						17,505
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						29,972
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 47,477				47,477
Accumulated Depreciation at December 31, 2016		$ 8,391				$ 8,391
Year of Construction		Jan. 1, 1988
Date of Acquisition		Mar. 1, 2011
Net Rentable Area | ft²						137,000
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 47,477
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 8,391
Braddock Place Member
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					$ 18,817
Initial Cost, Buildings and Improvements	[1]					71,250
Net Improvements (Retirement) since Acquisition						(14,808)
Gross Amounts at Which Carried at December 31, 2016, Land						16,615
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						58,644
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 75,259				75,259
Accumulated Depreciation at December 31, 2016		$ 6,725				6,725
Year of Construction		Jan. 1, 1985
Date of Acquisition		Sep. 1, 2011
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 75,259
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 6,725
John Marshall II Member
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					13,490
Initial Cost, Buildings and Improvements	[1]					53,024
Net Improvements (Retirement) since Acquisition						6,351
Gross Amounts at Which Carried at December 31, 2016, Land						13,490
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						59,375
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 72,865				72,865
Accumulated Depreciation at December 31, 2016		$ 13,754				$ 13,754
Year of Construction		Jan. 1, 1996
Date of Acquisition		Sep. 1, 2011
Net Rentable Area | ft²						223,000
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 72,865
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 13,754
Fairgate at Ballston [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					$ 17,750
Initial Cost, Buildings and Improvements	[1]					29,885
Net Improvements (Retirement) since Acquisition						5,794
Gross Amounts at Which Carried at December 31, 2016, Land						17,750
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						35,679
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 53,429				53,429
Accumulated Depreciation at December 31, 2016		$ 9,075				$ 9,075
Year of Construction		Jan. 1, 1988
Date of Acquisition		Jun. 1, 2012
Net Rentable Area | ft²						146,000
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 53,429
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 9,075
The Army Navy Club Building [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Washington, DC
Initial Cost, Land	[1],[6]					$ 30,796
Initial Cost, Buildings and Improvements	[1],[6]					39,315
Net Improvements (Retirement) since Acquisition	[6]					10,642
Gross Amounts at Which Carried at December 31, 2016, Land	[6]					30,796
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements	[6]					49,957
Gross Amounts at Which Carried at December 31, 2016, Total	[2],[6]	$ 80,753				80,753
Accumulated Depreciation at December 31, 2016	[6]	$ 7,583				$ 7,583
Year of Construction		Jan. 1, 1912
Date of Acquisition		Mar. 1, 2014
Net Rentable Area | ft²						109,000
Depreciation Life	[5]	30 years
Loans Payable	[9]					$ 0			49,618
Properties under development or held for future development						4,800
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2],[6]	$ 80,753
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period	[6]	$ 7,583
1775 Eye Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Washington, DC
Initial Cost, Land	[1]					48,086
Initial Cost, Buildings and Improvements	[1]					51,074
Net Improvements (Retirement) since Acquisition						8,473
Gross Amounts at Which Carried at December 31, 2016, Land						48,086
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						59,547
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 107,633				107,633
Accumulated Depreciation at December 31, 2016		$ 10,842				$ 10,842
Year of Construction		Jan. 1, 1964
Date of Acquisition		May 1, 2014
Net Rentable Area | ft²						188,000
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 107,633
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		10,842
Retail Centers [Member]
Real Estate and Accumulated Depreciation [Line Items]
Initial Cost, Land						$ 120,969
Initial Cost, Buildings and Improvements						249,498
Net Improvements (Retirement) since Acquisition						84,817
Gross Amounts at Which Carried at December 31, 2016, Land						120,622
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						334,662
Gross Amounts at Which Carried at December 31, 2016, Total		455,284				455,284
Accumulated Depreciation at December 31, 2016		138,380				$ 138,380
Net Rentable Area | ft²						2,333,000
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period		455,284
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 138,380
Takoma Park [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Maryland
Initial Cost, Land	[1]					$ 415
Initial Cost, Buildings and Improvements	[1]					1,084
Net Improvements (Retirement) since Acquisition						245
Gross Amounts at Which Carried at December 31, 2016, Land						366
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						1,378
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 1,744				1,744
Accumulated Depreciation at December 31, 2016		$ 1,198				$ 1,198
Year of Construction		Jan. 1, 1962
Date of Acquisition		Jul. 1, 1963
Net Rentable Area | ft²						51,000
Depreciation Life	[5]	50 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 1,744
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 1,198
Westminster [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Maryland
Initial Cost, Land	[1]					$ 519
Initial Cost, Buildings and Improvements	[1]					1,775
Net Improvements (Retirement) since Acquisition						9,899
Gross Amounts at Which Carried at December 31, 2016, Land						519
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						11,674
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 12,193				12,193
Accumulated Depreciation at December 31, 2016		$ 7,948				$ 7,948
Year of Construction		Jan. 1, 1969
Date of Acquisition		Sep. 1, 1972
Net Rentable Area | ft²						150,000
Depreciation Life	[5]	37 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 12,193
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 7,948
Concord Centre [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					$ 413
Initial Cost, Buildings and Improvements	[1]					850
Net Improvements (Retirement) since Acquisition						5,936
Gross Amounts at Which Carried at December 31, 2016, Land						413
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						6,786
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 7,199				7,199
Accumulated Depreciation at December 31, 2016		$ 3,619				$ 3,619
Year of Construction		Jan. 1, 1960
Date of Acquisition		Dec. 1, 1973
Net Rentable Area | ft²						75,000
Depreciation Life	[5]	33 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 7,199
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 3,619
Wheaton Park [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Maryland
Initial Cost, Land	[1]					$ 796
Initial Cost, Buildings and Improvements	[1]					857
Net Improvements (Retirement) since Acquisition						4,853
Gross Amounts at Which Carried at December 31, 2016, Land						796
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						5,710
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 6,506				6,506
Accumulated Depreciation at December 31, 2016		$ 4,114				$ 4,114
Year of Construction		Jan. 1, 1967
Date of Acquisition		Sep. 1, 1977
Net Rentable Area | ft²						74,000
Depreciation Life	[5]	50 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 6,506
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 4,114
Bradlee [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					$ 4,152
Initial Cost, Buildings and Improvements	[1]					5,383
Net Improvements (Retirement) since Acquisition						14,348
Gross Amounts at Which Carried at December 31, 2016, Land						4,152
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						19,731
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 23,883				23,883
Accumulated Depreciation at December 31, 2016		$ 12,571				$ 12,571
Year of Construction		Jan. 1, 1955
Date of Acquisition		Dec. 1, 1984
Net Rentable Area | ft²						172,000
Depreciation Life	[5]	40 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 23,883
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 12,571
Chevy Chase Metro Plaza [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Washington, DC
Initial Cost, Land	[1]					$ 1,549
Initial Cost, Buildings and Improvements	[1]					4,304
Net Improvements (Retirement) since Acquisition						8,298
Gross Amounts at Which Carried at December 31, 2016, Land						1,549
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						12,602
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 14,151				14,151
Accumulated Depreciation at December 31, 2016		$ 7,366				$ 7,366
Year of Construction		Jan. 1, 1975
Date of Acquisition		Sep. 1, 1985
Net Rentable Area | ft²						49,000
Depreciation Life	[5]	50 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 14,151
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 7,366
Shoppes of Foxchase [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					$ 5,838
Initial Cost, Buildings and Improvements	[1]					2,979
Net Improvements (Retirement) since Acquisition						14,812
Gross Amounts at Which Carried at December 31, 2016, Land						5,838
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						17,791
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 23,629				23,629
Accumulated Depreciation at December 31, 2016		$ 7,914				$ 7,914
Year of Construction		Jan. 1, 1960
Date of Acquisition		Jun. 1, 1994
Net Rentable Area | ft²						134,000
Depreciation Life	[5]	50 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 23,629
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 7,914
Frederick County Square [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Maryland
Initial Cost, Land	[1]					$ 6,561
Initial Cost, Buildings and Improvements	[1]					6,830
Net Improvements (Retirement) since Acquisition						5,376
Gross Amounts at Which Carried at December 31, 2016, Land						6,561
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						12,206
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 18,767				18,767
Accumulated Depreciation at December 31, 2016		$ 8,302				$ 8,302
Year of Construction		Jan. 1, 1973
Date of Acquisition		Aug. 1, 1995
Net Rentable Area | ft²						228,000
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 18,767
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 8,302
800 S. Washington Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Virginia
Initial Cost, Land	[1]					$ 2,904
Initial Cost, Buildings and Improvements	[1]					5,489
Net Improvements (Retirement) since Acquisition						5,954
Gross Amounts at Which Carried at December 31, 2016, Land						2,904
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						11,443
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 14,347				14,347
Accumulated Depreciation at December 31, 2016		$ 5,485				$ 5,485
Year of Construction		Jan. 1, 1951
Date of Acquisition		Jun. 1, 1998
Net Rentable Area | ft²						46,000
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 14,347
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 5,485
Centre at Hagerstown . [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Maryland
Initial Cost, Land	[1]					$ 13,029
Initial Cost, Buildings and Improvements	[1]					25,415
Net Improvements (Retirement) since Acquisition						2,144
Gross Amounts at Which Carried at December 31, 2016, Land						13,029
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						27,559
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 40,588				40,588
Accumulated Depreciation at December 31, 2016		$ 14,358				$ 14,358
Year of Construction		Jan. 1, 2000
Date of Acquisition		Jun. 1, 2002
Net Rentable Area | ft²						333,000
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 40,588
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 14,358
Frederick Crossing [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Maryland
Initial Cost, Land	[1]					$ 12,759
Initial Cost, Buildings and Improvements	[1]					35,477
Net Improvements (Retirement) since Acquisition						2,070
Gross Amounts at Which Carried at December 31, 2016, Land						12,759
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						37,547
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 50,306				50,306
Accumulated Depreciation at December 31, 2016		$ 16,709				$ 16,709
Year of Construction		Jan. 1, 1999
Date of Acquisition		Mar. 1, 2005
Net Rentable Area | ft²						295,000
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 50,306
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 16,709
Randolph Shopping Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Maryland
Initial Cost, Land	[1]					$ 4,928
Initial Cost, Buildings and Improvements	[1]					13,025
Net Improvements (Retirement) since Acquisition						1,188
Gross Amounts at Which Carried at December 31, 2016, Land						4,928
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						14,213
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 19,141				19,141
Accumulated Depreciation at December 31, 2016		$ 5,809				$ 5,809
Year of Construction		Jan. 1, 1972
Date of Acquisition		May 1, 2006
Net Rentable Area | ft²						83,000
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 19,141
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 5,809
Montrose Shopping Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Maryland
Initial Cost, Land	[1]					$ 11,612
Initial Cost, Buildings and Improvements	[1]					22,410
Net Improvements (Retirement) since Acquisition						2,285
Gross Amounts at Which Carried at December 31, 2016, Land						11,020
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						25,287
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 36,307				36,307
Accumulated Depreciation at December 31, 2016		$ 10,105				$ 10,105
Year of Construction		Jan. 1, 1970
Date of Acquisition		May 1, 2006
Net Rentable Area | ft²						147,000
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 36,307
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 10,105
Gateway Overlook [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Maryland
Initial Cost, Land	[1]					$ 28,816
Initial Cost, Buildings and Improvements	[1]					52,249
Net Improvements (Retirement) since Acquisition						763
Gross Amounts at Which Carried at December 31, 2016, Land						29,110
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						52,718
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 81,828				81,828
Accumulated Depreciation at December 31, 2016		$ 18,937				$ 18,937
Year of Construction		Jan. 1, 2007
Date of Acquisition		Dec. 1, 2010
Net Rentable Area | ft²						220,000
Depreciation Life	[5]	30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 81,828
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 18,937
Olney Village Center Member
Real Estate and Accumulated Depreciation [Line Items]
Location		Maryland
Initial Cost, Land	[1],[6]					$ 15,842
Initial Cost, Buildings and Improvements	[1],[6]					39,133
Net Improvements (Retirement) since Acquisition	[6]					2,114
Gross Amounts at Which Carried at December 31, 2016, Land	[6]					15,842
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements	[6]					41,247
Gross Amounts at Which Carried at December 31, 2016, Total	[2],[6]	$ 57,089				57,089
Accumulated Depreciation at December 31, 2016		$ 9,768				$ 9,768
Year of Construction		Jan. 1, 1979
Date of Acquisition	[6]	Aug. 1, 2011
Net Rentable Area | ft²						198,000
Depreciation Life	[5]	30 years
Loans Payable						$ 13,091			14,851
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2],[6]	$ 57,089
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 9,768
Spring Vally Retail Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Washington, DC
Initial Cost, Land	[1]					10,836
Initial Cost, Buildings and Improvements	[1]					32,238
Net Improvements (Retirement) since Acquisition						4,532
Gross Amounts at Which Carried at December 31, 2016, Land						10,836
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						36,770
Gross Amounts at Which Carried at December 31, 2016, Total	[2]	$ 47,606				47,606
Accumulated Depreciation at December 31, 2016		$ 4,177				$ 4,177
Year of Construction		Jan. 1, 1941
Date of Acquisition		Oct. 1, 2014
Net Rentable Area | ft²						78,000
Depreciation Life	[5]	30 years
Properties under development or held for future development						$ 3,600
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period	[2]	$ 47,606
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 4,177
Watergate 600 [Member]
Real Estate and Accumulated Depreciation [Line Items]
Location		Washington, DC
Initial Cost, Land						45,981
Initial Cost, Buildings and Improvements						78,325
Net Improvements (Retirement) since Acquisition						10,192
Gross Amounts at Which Carried at December 31, 2016, Land						45,981
Gross Amounts at Which Carried at December 31, 2016, Buildings and Improvements						88,517
Gross Amounts at Which Carried at December 31, 2016, Total		$ 134,498				134,498
Accumulated Depreciation at December 31, 2016		$ 3,384				3,384
Year of Construction		Jan. 1, 1972
Date of Acquisition		Apr. 1, 2017
Net Rentable Area | ft²								293,000
Depreciation Life		30 years
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, end of period		$ 134,498
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, end of period		$ 3,384
Riverside Developments [Member]
Real Estate and Accumulated Depreciation [Line Items]
Properties under development or held for future development						19,200			$ 19,200
Army Navy Building and Spring Valley Village [Member]
Real Estate and Accumulated Depreciation [Line Items]
Properties under development or held for future development						$ 5,500
[1]	The purchase cost of real estate investments has been divided between land and buildings and improvements on the basis of management’s determination of the fair values.
[2]	At December 31, 2017, total land, buildings and improvements are carried at $1,983.3 million for federal income tax purposes.
[3]	As of December 31, 2017, Washington REIT had under development multifamily properties, the Wellington land parcel (Trove) and Riverside Apartments land parcel. The value not yet placed into service at December 31, 2017 was $29.7 million and $19.2 million, respectively.
[4]	Includes non-cash accruals for capital items.
[5]	The useful life shown is for the main structure. Buildings and improvements are depreciated over various useful lives ranging from 3 to 50 years.
[6]	At December 31, 2017, our properties were encumbered by non-recourse mortgage amounts as follows: $32.2 million on The Kenmore, $13.1 million on Olney Village Center and $46.6 million on Yale West. Mortgage amounts exclude premiums and debt loan costs.
[7]	The maturity date of the mortgage note is January 1, 2052, but can be prepaid, without penalty, beginning on January 31, 2022.
[8]	As of December 31, 2017, Washington REIT had investments in various development, redevelopment and renovation projects, including Spring Valley Village and The Ashby at McLean. The total value of these projects, which has not yet been placed in service, is $5.5 million at December 31, 2017
[9]	The note was prepaid without penalty in February 2017.