First Potomac Realty Trust (FPO) 10-Q 1 May 15 2015 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2015	Apr. 29, 2015
Document And Entity Information [Abstract]
Entity Registrant Name	FIRST POTOMAC REALTY TRUST
Document Type	10-Q
Amendment Flag	FALSE
Document Period End Date	31-Mar-15
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Entity Central Index Key	1254595
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		58,726,808

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Assets:
Rental property, net	$1,292,895	$1,288,873
Assets held-for-sale	0	59,717
Cash and cash equivalents	14,686	13,323
Escrows and reserves	2,298	2,986
Accounts and other receivables, net of allowance for doubtful accounts of $1,386 and $1,207, respectively	10,290	10,587
Accrued straight-line rents, net of allowance for doubtful accounts of $133 and $104, respectively	36,761	34,226
Notes receivable, net	34,000	63,679
Investment in affiliates	47,658	47,482
Deferred costs, net	44,882	43,991
Prepaid expenses and other assets	8,049	7,712
Intangible assets, net	42,929	45,884
Total assets	1,534,448	1,618,460
Liabilities:
Mortgage and Construction loans	303,866	305,139
Unsecured term loan	300,000	300,000
Unsecured revolving credit facility	143,000	205,000
Disposal Group, Including Discontinued Operation, Liabilities	0	4,562
Accounts payable and other liabilities	37,107	41,113
Accrued interest	1,694	1,720
Rents received in advance	8,018	7,971
Tenant security deposits	6,136	5,891
Deferred market rent, net	2,667	2,827
Total liabilities	802,488	874,223
Noncontrolling interests in the Operating Partnership	32,198	33,332
Equity:
Common shares, $0.001 par value, 150,000 shares authorized; 58,727 and 58,815 shares issued and outstanding, respectively	59	59
Additional paid-in capital	914,447	913,282
Noncontrolling interests in a consolidated partnership	802	898
Accumulated other comprehensive loss	-4,298	-3,268
Dividends in excess of accumulated earnings	-371,248	-360,066
Total equity	699,762	710,905
Total liabilities, noncontrolling interests and equity	1,534,448	1,618,460
Series A Preferred Shares
Equity:
Series A Preferred Shares, $25 per share liquidation preference, 6,400 shares issued and outstanding	$160,000	$160,000

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, except Share data, unless otherwise specified
Statement of Financial Position [Abstract]
Allowance for doubtful accounts, accounts and other receivables	$1,386	$1,207
Allowance for doubtful accounts, accrued straight-line rents	$133	$104
Preferred stock, par value	$0.00	$0.00
Preferred stock, shares authorized	50,000,000	50,000,000
Series A Preferred Shares liquidation preference	$25	$25
Series A Preferred Shares, shares issued	6,400,000	6,400,000
Series A Preferred Shares, shares outstanding	6,400,000	6,400,000
Common stock, par value	$0.00	$0.00
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	58,727,000	58,815,000
Common stock, shares outstanding	58,727,000	58,815,000

Consolidated_Statements_of_Ope

Consolidated Statements of Operations (USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Revenues:
Rental	$34,379	$30,433
Tenant reimbursements and other	9,470	8,930
Total revenues	43,849	39,363
Operating expenses:
Property operating	13,113	12,038
Real estate taxes and insurance	5,042	4,132
General and administrative	5,526	5,196
Acquisition costs	0	68
Depreciation and amortization	16,335	14,310
Total operating expenses	40,016	35,744
Operating income	3,833	3,619
Other expenses (income)
Interest expense	6,908	5,737
Interest and other income	-3,828	-1,759
Equity in (earnings) losses of affiliates	-346	227
Total other expenses (income)	2,734	4,205
Income (loss) from continuing operations	1,099	-586
Discontinued operations:
Loss from operations	-975	-911
Loss on debt extinguishment	-489	0
Gain on sale of rental property	857	54
Loss from discontinued operations	-607	-857
Net income (loss)	492	-1,443
Less: Net loss attributable to noncontrolling interests	112	195
Net income (loss) attributable to First Potomac Realty Trust	604	-1,248
Less: Dividends on preferred shares	-3,100	-3,100
Net loss attributable to common shareholders	($2,496)	($4,348)
Basic and diluted earnings per common share:
Loss from continuing operations	($0.03)	($0.07)
Loss from discontinued operations	($0.01)	($0.01)
Net loss	($0.04)	($0.08)
Weighted average common shares outstanding:
Basic and diluted	58,225	58,097
Diluted	58,225	58,097

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive (Loss) Income (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income (loss)	$492	($1,443)
Unrealized gain on derivative instruments	164	317
Unrealized loss on derivative instruments	-1,240	-142
Total comprehensive loss	-584	-1,268
Net loss attributable to noncontrolling interests	112	195
Net loss (gain) from derivative instruments attributable to noncontrolling interests	46	-7
Comprehensive loss attributable to First Potomac Realty Trust	($426)	($1,080)

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Cash flows from operating activities:
Net income (loss)	$492	($1,443)
Discontinued operations:
Gain on sale of rental property	-857	-54
Depreciation and amortization	1,222	1,249
Depreciation and amortization	16,603	14,572
Stock based compensation	700	823
Bad debt expense	302	111
Amortization of deferred market rent	30	-56
Amortization of financing costs and discounts	279	266
Equity in (earnings) losses of affiliates	-346	227
Distributions from investments in affiliates	171	106
Changes in assets and liabilities:
Escrows and reserves	688	4,010
Accounts and other receivables	-120	-2,623
Accrued straight-line rents	-1,737	-1,442
Prepaid expenses and other assets	-591	651
Tenant security deposits	-464	58
Accounts payable and accrued expenses	279	-2,189
Accrued interest	-26	-17
Rents received in advance	-291	-593
Deferred costs	-3,362	-2,210
Total adjustments	12,480	12,889
Net cash provided by operating activities	12,972	11,446
Cash flows from investing activities:
Investment in note receivable	0	-9,000
Purchase deposit on future acquisition	0	-2,000
Proceeds from sale of rental property	56,943	31,616
Principal payments from note receivable	29,720	52
Additions to rental property and furniture, fixtures and equipment	-15,881	-8,297
Additions to construction in progress	-3,361	-3,096
Net cash provided by investing activities	67,421	9,275
Cash flows from financing activities:
Financing costs	-8	-2
Issuance of debt	13,000	27,794
Repayments of debt	-79,648	-30,296
Dividends to common shareholders	-8,802	-8,789
Dividends to preferred shareholders	-3,100	-3,100
Contributions from consolidated joint venture partners	0	89
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders	-96	0
Distributions to noncontrolling interests	-395	-394
Proceeds from stock option exercises	19	79
Net cash used in financing activities	-79,030	-14,619
Net increase in cash and cash equivalents	1,363	6,102
Cash and cash equivalents, beginning of period	13,323	8,740
Cash and cash equivalents, end of period	14,686	14,842
Cash paid for interest, net	6,553	5,373
Non-cash investing and financing activities:
Value of common shares retired to settle employee income tax obligations	437	383
Change in fair value of the outstanding common Operating Partnership units	-581	2,027
Issuance of common Operating Partnership units in connection with the acquisition of rental property	0	40
Changes in accruals:
Additions to rental property and furniture, fixtures and equipment	-3,083	371
Additions to development and redevelopment	$514	($1,768)

Consolidated_Statements_of_Cas1

Consolidated Statements of Cash Flows (Parenthetical) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Capitalized interest on indebtedness paid in cash	$400,000	$800,000
Surrendered common shares to satisfy statutory minimum federal income tax obligations	400,000	0
Change in redemption value, noncontrolling interest	4,200,000	5,300,000
Operating Partnership units issued for acquisition	0
Furniture and Fixtures [Member]
Accrued capital expenditure	8,200,000	6,600,000
Development and Redevelopment [Member]
Accrued capital expenditure	800,000	1,900,000
840 First Street, NE [Member]
Operating Partnership units issued for acquisition		3,125
Operating Partnership units fair valued	$40,000

Description_of_Business

Description of Business	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Description of Business	Description of Business
	First Potomac Realty Trust (the “Company”) is a leader in the ownership, management, development and redevelopment of office and business park properties in the greater Washington, D.C. region. The Company strategically focuses on acquiring and redeveloping properties that it believes can benefit from its intensive property management, leasing expertise, market knowledge and established relationships, and seeks to reposition these properties to increase their profitability and value. The Company’s portfolio primarily contains a mix of single-tenant and multi-tenant office properties and business parks. Office properties are single-story and multi-story buildings that are primarily for office use; and business parks contain buildings with office features combined with some industrial property space. The Company separates its properties into four distinct reporting segments, which it refers to as the Washington, D.C., Maryland, Northern Virginia and Southern Virginia reporting segments.
	References in these unaudited condensed consolidated financial statements to “we,” “our,” “us,” “the Company” or “First Potomac,” refer to the Company and its subsidiaries, on a consolidated basis, unless the context indicates otherwise.
	We conduct our business through First Potomac Realty Investment Limited Partnership, our operating partnership (the “Operating Partnership”). We are the sole general partner of, and, as of March 31, 2015, owned 100% of the preferred interest and 95.7% of the common interest in the Operating Partnership. The remaining common interests in the Operating Partnership, which are presented as noncontrolling interests in the Operating Partnership in the accompanying unaudited condensed consolidated financial statements, are limited partnership interests, some of which are owned by two of our executive officers who contributed properties and other assets to us upon our formation, and the remainder of which are owned by other unrelated parties.
	At March 31, 2015, we wholly owned or had a controlling interest in properties totaling 8.0 million square feet and had a noncontrolling ownership interest in properties totaling an additional 0.9 million square feet through five unconsolidated joint ventures. We also owned land that can support 1.3 million square feet of additional development. Our consolidated properties were 88.0% occupied by 500 tenants at March 31, 2015. We did not include square footage that was in development or redevelopment, which totaled 0.2 million square feet at March 31, 2015, in our occupancy calculation. We derive substantially all of our revenue from leases of space within our properties. As of March 31, 2015, our largest tenant was the U.S. Government, which accounted for 13.2% of our total annualized cash basis rent, and the U.S. Government combined with government contractors, accounted for 25.9% of our total annualized cash basis rent as of March 31, 2015. We operate so as to qualify as a real estate investment trust (“REIT”) for federal income tax purposes.

Summary_of_Significant_Account

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies
	(a) Principles of Consolidation
	Our unaudited condensed consolidated financial statements include our accounts and the accounts of our Operating Partnership and the subsidiaries in which we or our Operating Partnership has a controlling interest, which includes First Potomac Management LLC, a wholly-owned subsidiary that manages the majority of our properties. All intercompany balances and transactions have been eliminated in consolidation.
	We have condensed or omitted certain information and note disclosures normally included in financial statements presented in accordance with U.S. generally accepted accounting principles (“GAAP”) in the accompanying unaudited condensed consolidated financial statements. We believe the disclosures made are adequate to prevent the information presented from being misleading. However, the unaudited condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto included in our annual report on Form 10-K for the year ended December 31, 2014 and as updated from time to time in other filings with the SEC.
	In our opinion, the accompanying unaudited condensed consolidated financial statements reflect all adjustments, consisting of normal recurring adjustments and accruals necessary to present fairly our financial position as of March 31, 2015 and the results of our operations, our comprehensive loss and our cash flows for the three months ended March 31, 2015 and 2014. Interim results are not necessarily indicative of full-year performance due, in part, to the timing of transactions and the impact of acquisitions and dispositions throughout the year as well as the seasonality of certain operating expenses such as utilities expense and snow and ice removal costs.
	(b) Use of Estimates
	The preparation of condensed consolidated financial statements in conformity with GAAP requires our management team to make a number of estimates and assumptions relating to the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the unaudited condensed consolidated financial statements and the reported amounts of revenues and expenses during the period. Estimates include the amount of accounts receivable that may be uncollectible; recoverability of notes receivable, future cash flows, discount and capitalization rate assumptions used to fair value acquired properties and to test impairment of certain long-lived assets and goodwill; derivative valuations; market lease rates, lease-up periods, leasing and tenant improvement costs used to fair value intangible assets acquired and probability weighted cash flow analysis used to fair value contingent liabilities. Actual results could differ from those estimates.
	(c) Rental Property
	Rental property is initially recorded at fair value, if acquired in a business combination, or initial cost when constructed or acquired in an asset purchase. Improvements and replacements are capitalized at cost when they extend the useful life, increase capacity or improve the efficiency of the asset. Repairs and maintenance are charged to expense when incurred. Depreciation and amortization are recorded on a straight-line basis over the estimated useful lives of the assets. The estimated useful lives of our assets, by class, are as follows:
	Buildings	39 years
	Building improvements	5 to 20 years
	Furniture, fixtures and equipment	5 to 15 years
	Lease related intangible assets	The term of the related lease
	Tenant improvements	Shorter of the useful life of the asset or the term of the related lease
	We regularly review market conditions for possible impairment of a property’s carrying value. When circumstances such as adverse market conditions, changes in management’s intended holding period or potential sale to a third party indicate a possible impairment of the carrying value of a property, an impairment analysis is performed. We assess potential impairments based on an estimate of the future undiscounted cash flows (excluding interest charges) expected to result from the property’s use and eventual disposition. This estimate is based on projections of future revenues, expenses, capital improvement costs to maintain the operating capacity, expected holding periods and capitalization rates. These cash flows consider factors such as expected market trends and leasing prospects, as well as the effects of leasing demand, competition and other factors. If impairment exists due to the inability to recover the carrying value of a real estate investment based on forecasted undiscounted cash flows, an impairment loss is recorded to the extent that the carrying value exceeds the estimated fair value of the property. Further, we will record an impairment loss if we expect to dispose of a property, in the near term, at a price below carrying value. In such an event, we will record an impairment loss based on the difference between a property’s carrying value and its projected sales price less any estimated costs to sell.
	We will classify a building as held-for-sale in accordance with GAAP in the period in which we have made the decision to dispose of the building, our Board of Trustees or a designated delegate has approved the sale, there is a high likelihood a binding agreement to purchase the property will be signed under which the buyer will be required to commit a significant amount of nonrefundable cash and no significant financing contingencies exist that could cause the transaction not to be completed in a timely manner. We will cease recording depreciation on a building once it has been classified as held-for-sale. In the second quarter of 2014, we prospectively adopted Accounting Standards Update 2014-08, Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity (“ASU 2014-08”), which impacts the presentation of operations and gains or losses from disposed properties and properties classified as held-for-sale. ASU 2014-08 states that a disposal of a component of an entity or a group of components of an entity is required to be reported in discontinued operations only if the disposal represents a strategic shift that has, or will have, a major effect on an entity’s operations or financial results. The operations of all properties that were sold prior to the adoption of ASU 2014-08, two properties that were classified as held-for-sale in previously issued financial statements prior to our adoption of ASU 2014-08 (West Park and Patrick Center) and were subsequently sold, as well as the Richmond Portfolio (as defined below), are reflected within discontinued operations in our consolidated statements of operations for all periods presented.
	If the building does not qualify as a discontinued operation under ASU 2014-08, we will classify the building's operating results, together with any impairment charges and any gains or losses on the sale of the building, in continuing operations for all periods presented in our consolidated statements of operations. We will classify the assets and liabilities related to the building as held-for-sale in our consolidated balance sheet for the period the held-for-sale criteria were met.
	If the building does qualify as a discontinued operation under ASU 2014-08, we will classify the building's operating results, together with any impairment charges and any gains or losses on the sale of the building, in discontinued operations in our consolidated statements of operations for all periods presented and classify the assets and liabilities related to the building as held-for-sale in our consolidated balance sheets for the periods presented. Interest expense is reclassified to discontinued operations only to the extent the disposed or held-for-sale property is secured by specific mortgage debt and the mortgage debt will not be assigned to another property owned by us after the disposition.
	We recognize the fair value, if sufficient information exists to reasonably estimate the fair value, of any liability for conditional asset retirement obligations when assumed or incurred, which is generally upon acquisition, construction, development or redevelopment and/or through the normal operation of the asset.
	We capitalize interest costs incurred on qualifying expenditures for real estate assets under development or redevelopment, which include our investments in assets owned through unconsolidated joint ventures that are under development or redevelopment, while being readied for their intended use in accordance with accounting requirements regarding capitalization of interest. We will capitalize interest when qualifying expenditures for the asset have been made, activities necessary to get the asset ready for its intended use are in progress and interest costs are being incurred. Capitalized interest also includes interest associated with expenditures incurred to acquire developable land while development activities are in progress. We also capitalize direct compensation costs of our construction personnel who manage the development and redevelopment projects, but only to the extent the employee’s time can be allocated to a project. Any portion of construction management costs not directly attributable to a specific project are recognized as general and administrative expense in the period incurred. We do not capitalize any other general and administrative costs such as office supplies, office rent expense or an overhead allocation to our development or redevelopment projects. Capitalized compensation costs were immaterial for the three months ended March 31, 2015 and 2014. Capitalization of interest ends when the asset is substantially complete and ready for its intended use, but no later than one year from completion of major construction activity, if the property is not occupied. We place redevelopment and development assets into service at this time and commence depreciation upon the substantial completion of tenant improvements and the recognition of revenue. Capitalized interest is depreciated over the useful life of the underlying assets, commencing when those assets are placed into service.
	(d) Notes Receivable
	We provide loans to the owners of real estate properties, which can be collateralized by interest in the real estate property. We record these loans as “Notes receivable, net” in our consolidated balance sheets. The loans are recorded net of any discount or issuance costs, which are amortized over the life of the respective note receivable using the effective interest method. We record interest earned from notes receivable and amortization of any discount costs or issuance costs within “Interest and other income” in our consolidated statements of operations.
	We will establish a provision for anticipated credit losses associated with our notes receivable when we anticipate that we may be unable to collect any contractually due amounts. This determination is based upon such factors as delinquencies, loss experience, collateral quality and current economic or borrower conditions. Our collectability of our notes receivable may be adversely impacted by the financial stability of the Washington, D.C. region and the ability of the underlying assets to keep current tenants or attract new tenants. Estimated losses are recorded as a charge to earnings to establish an allowance for credit losses that we estimate to be adequate based on these factors. Based on the review of the above criteria, we did not record an allowance for credit losses for our notes receivable during the three months ended March 31, 2015 and 2014.
	(e) Application of New Accounting Standards
	In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update 2014-09, Revenue from Contracts with Customers (“ASU 2014-09”), which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. ASU 2014-09 will replace most existing revenue recognition guidance when it becomes effective on January 1, 2017. Early adoption is not permitted. ASU 2014-09 permits the use of either the retrospective or cumulative effect transition method. We have not yet selected a transition method and are evaluating the impact that ASU 2014-09 will have on our consolidated financial statements or related disclosures.
	In August 2014, the FASB issued Accounting Standards Update 2014-15, Disclosure of Uncertainties about an Entity's Ability to Continue as a Going Concern (“ASU 2014-15”), which requires an entity to evaluate whether conditions or events, in the aggregate, raise substantial doubt about the entity's ability to continue as a going concern for one year from the date the financial statements are issued or are available to be issued. The guidance will become effective January 1, 2017. The adoption of ASU 2014-15 is not expected to have an impact on our consolidated financial statements or related disclosures.
	In January 2015, the FASB issued Accounting Standards Update 2015-01, Simplifying Income Statement Presentation by Eliminating the Concept of Extraordinary Items ("ASU 2015-01"), which eliminates the concept of extraordinary items from GAAP and the requirement that an entity separately report extraordinary items in the income statement. ASU 2015-01 also requires that entities continue to evaluate whether items are unusual in nature or infrequent in occurrence for presentation and disclosure purposes. ASU 2015-01 applies to all entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2015. Early adoption is permitted and the guidance may be applied prospectively or retrospectively to all prior periods presented in the consolidated financial statements. The adoption of ASU 2015-01 is not expected to have a material impact on our consolidated financial statements or related disclosures.
	In February 2015, the FASB issued Accounting Standards Update 2015-02, Amendments to the Consolidation Analysis (“ASU 2015-02”), which makes certain changes to both the variable interest model and the voting model, including changes to the identification of variable interests (fees paid to a decision maker or service provider), the variable interest entity characteristics for a limited partnership or similar entity and the primary beneficiary determination. ASU 2015-02 is effective January 1, 2016. The adoption of ASU 2015-02 is not expected to have a material impact on our consolidated financial statements or related disclosures.
	In April 2015, the FASB issued Accounting Standards Update No. 2015-03, Simplifying the Presentation of Debt Issuance Costs (“ASU 2015-03”), which requires debt issuance costs to be presented in the balance sheet as a direct deduction from the carrying value of the debt liability. ASU 2015-03 is effective for periods beginning after December 15, 2015 with early adoption permitted and will be applied on a retrospective basis. The guidance will be effective on January 1, 2016 and is not expected to have a material impact on our consolidated financial statements or related disclosures.
	(f) Reclassifications
	Certain prior year amounts have been reclassified to conform to the current year presentation as a result of reclassifying the operating results of several properties as discontinued operations. For more information, see note 7, Dispositions.

Earnings_Per_Common_Share

Earnings Per Common Share	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Earnings Per Common Share	Earnings Per Common Share
	Basic earnings or loss per common share (“EPS”) is calculated by dividing net income or loss attributable to common shareholders by the weighted average common shares outstanding for the periods presented. Diluted EPS is computed after adjusting the basic EPS computation for the effect of dilutive common equivalent shares outstanding during the periods presented, which include stock options, non-vested shares and preferred shares. We apply the two-class method for determining EPS as our outstanding unvested shares with non-forfeitable dividend rights are considered participating securities. Our excess of distributions over earnings related to participating securities is shown as a reduction in total earnings attributable to common shareholders in our computation of EPS.
	The following table sets forth the computation of our basic and diluted earnings per common share (amounts in thousands, except per share amounts):
		Three Months Ended March 31,
		2015				2014
	Numerator for basic and diluted earnings per common share:
	Income (loss) from continuing operations	$	1,099			$	(586	)
	Loss from discontinued operations	(607		)		(857		)
	Net income (loss)	492				(1,443		)
	Less: Net loss from continuing operations attributable to noncontrolling interests	86				155
	Less: Net loss from discontinued operations attributable to noncontrolling interests	26				40
	Net income (loss) attributable to First Potomac Realty Trust	604				(1,248		)
	Less: Dividends on preferred shares	(3,100		)		(3,100		)
	Net loss attributable to common shareholders	(2,496		)		(4,348		)
	Less: Allocation to participating securities	(73		)		(78		)
	Net loss attributable to common shareholders	$	(2,569	)		$	(4,426	)
	Denominator for basic and diluted earnings per common share:
	Weighted average common shares outstanding - basic and diluted	58,225				58,097
	Basic and diluted earnings per common share:
	Loss from continuing operations	$	(0.03	)		$	(0.07	)
	Loss from discontinued operations	(0.01		)		(0.01		)
	Net loss	$	(0.04	)		$	(0.08	)
	In accordance with GAAP regarding earnings per common share, we did not include the following potential weighted average common shares in our calculation of diluted earnings per common share as they are anti-dilutive for the periods presented (amounts in thousands):
		Three Months Ended
		March 31,
		2015			2014
	Stock option awards	1,083			1,206
	Non-vested share awards	380			414
	Series A Preferred Shares(1)	13,032			12,671
		14,495			14,291
	(1)	Our Series A Preferred Shares are only convertible into our common shares upon certain changes in control of our Company. The dilutive shares are calculated as the daily average of the face value of the Series A Preferred Shares divided by the outstanding common share price.

Rental_Property

Rental Property	3 Months Ended
	Mar. 31, 2015
Real Estate [Abstract]
Rental Property	Rental Property
	Rental property represents buildings and related improvements, net of accumulated depreciation, and developable land that are wholly owned or owned by an entity in which we have a controlling interest. All of our rental properties are located within the greater Washington, D.C. region. Rental property consists of the following (dollars in thousands):
		March 31, 2015			December 31, 2014(1)
	Land and land improvements	$	325,228		$	325,214
	Buildings and improvements	950,746			949,683
	Construction in progress	73,444			69,181
	Tenant improvements	170,443			159,867
	Furniture, fixtures and equipment	402			427
		1,520,263			1,504,372
	Less: accumulated depreciation	(227,368		)	(215,499		)
		$	1,292,895		$	1,288,873
	(1) Excludes rental property totaling $57.7 million at December 31, 2014 related to the sale of the Richmond Portfolio (as defined in note 7, Dispositions), which was classified as held-for-sale at December 31, 2014 and was sold on March 19, 2015.
	Development and Redevelopment Activity
	We will place completed development and redevelopment assets in service upon the earlier of one year after major construction activity is deemed to be substantially complete or upon occupancy. We construct office buildings and/or business parks on a build-to-suit basis or with the intent to lease upon completion of construction. We own developable land that can accommodate 1.3 million square feet of additional building space, of which, 0.7 million is located in the Washington, D.C. reporting segment, 0.1 million in the Maryland reporting segment, 0.4 million in the Northern Virginia reporting segment and 0.1 million in the Southern Virginia reporting segment.
	During the third quarter of 2014, we signed a lease for 167,000 square feet at a to-be-constructed building in our Northern Virginia reporting segment on vacant land that we have in our portfolio. We currently expect to complete construction of the new building in the fourth quarter of 2016. At March 31, 2015, our total investment in the development project was $10.2 million, which included the original cost basis of the applicable portion of the vacant land of $5.2 million. The majority of the costs incurred as of March 31, 2015 in excess of the original cost basis of the land relate to site preparation costs.
	On August 4, 2011, we formed a joint venture, in which we have a 97% interest, with an affiliate of Perseus Realty, LLC to acquire Storey Park in our Washington, D.C. reporting segment. At the time, the site was leased to Greyhound Lines, Inc. (“Greyhound”), which subsequently relocated its operations. Greyhound’s lease expired on August 31, 2013, at which time the property was placed into development. The joint venture anticipates developing a mixed-use project on the 1.6 acre site, which can accommodate up to 712,000 square feet. At March 31, 2015, our total investment in the development project was $56.0 million, which included the original cost basis of the property of $43.3 million. The majority of the costs in excess of the original cost basis relate to capitalized architectural fees and site preparation costs. We are currently exploring our options related to this property; however, until a definitive plan for the property has been reached and we begin significant development activities, we cannot determine the total cost of the project or the anticipated completion date.
	On December 28, 2010, we acquired 440 First Street, NW, a vacant eight-story office building in our Washington, D.C. reporting segment. In October 2013, we substantially completed the redevelopment of the 139,000 square foot property. At March 31, 2015, the property was 58.9% leased and 46.9% occupied. During the fourth quarter of 2014, all vacant space at the property was placed in service. At March 31, 2015, our total investment in the redevelopment project was $55.5 million, which included the original cost basis of the property of $23.6 million.
	During the first quarter of 2015, we did not place in-service any completed development or redevelopment space. At March 31, 2015, we had no completed development or redevelopment space that have yet to be placed in service.

Notes_Receivable

Notes Receivable	3 Months Ended
	Mar. 31, 2015
Receivables [Abstract]
Notes Receivable	Notes Receivable
	Below is a summary of our notes receivable for our outstanding mezzanine loans (dollars in thousands):
		Balance at March 31, 2015
	Property	Face Amount		Unamortized			Balance		Interest Rate
				Origination Fees
	950 F Street, NW	$	34,000	$	—		$	34,000	9.75	%
		Balance at December 31, 2014
	Property	Face Amount		Unamortized			Balance		Interest Rate
				Origination Fees
	950 F Street, NW	$	34,000	$	—		$	34,000	9.75	%
	America’s Square	29,720		(41		)	29,679		9	%
		$	63,720	$	(41	)	$	63,679
	On February 24, 2015, the owners of America’s Square, a 461,000 square foot office complex located in Washington, D.C., prepaid a mezzanine loan that had an outstanding balance of $29.7 million. We provided the owners of America’s Square a $30.0 million loan in April 2011, which was secured by a portion of the owner’s interest in the property. The loan had a fixed-interest rate of 9.0% and was scheduled to mature on May 1, 2016. We received a yield maintenance payment of $2.4 million with the repayment of the loan. The proceeds from the loan repayment, including the yield maintenance payment, were used to pay down a portion of the outstanding balance of our unsecured revolving credit facility.
	In December 2010, we provided a $25.0 million mezzanine loan to the owners of 950 F Street, NW, a ten-story, 287,000 square-foot office/retail building located in Washington, D.C. that is secured by a portion of the owners’ interest in the property. The loan requires monthly interest-only payments with a constant interest rate over the life of the loan. On January 10, 2014, we amended the loan to increase the outstanding balance to $34.0 million and reduce the fixed interest rate from 12.5% to 9.75%. The amended mezzanine loan matures on April 1, 2017 and is repayable in full on or after December 21, 2015. The $9.0 million increase in the loan was provided by a draw under our unsecured revolving credit facility.
	We recorded interest income related to our notes receivable of $1.2 million and $1.5 million for the three months ended March 31, 2015 and 2014, respectively, which is included within “Interest and other income” in our consolidated statements of operations.
	We recorded income from the amortization of origination fees of $5 thousand and $11 thousand for the three months ended March 31, 2015 and 2014, respectively. During the first quarter of 2014, we wrote-off $0.1 million of unamortized fees related to the original 950 F Street, NW mezzanine loan. We recorded income from the yield maintenance payment of $2.4 million for the three months ended March 31, 2015. The yield maintenance payment and the amortization and write-off of unamortized fees are recorded within “Interest and other income” in our consolidated statements of operations.

Investment_in_Affiliates

Investment in Affiliates	3 Months Ended
	Mar. 31, 2015
Equity Method Investments and Joint Ventures [Abstract]
Investment in Affiliates	Investment in Affiliates
	We own an interest in several joint ventures that own properties. We do not control the activities that are most significant to the joint ventures. As a result, the assets, the liabilities and the operating results of these noncontrolled joint ventures are not consolidated within our unaudited condensed consolidated financial statements. Our investments in these joint ventures are recorded as “Investment in affiliates” in our consolidated balance sheets. Our investment in affiliates consisted of the following (dollars in thousands):
		Reporting Segment		Ownership			31-Mar-15		31-Dec-14
				Interest
	Prosperity Metro Plaza	Northern Virginia		51	%		$	24,846	$	24,651
	1750 H Street, NW	Washington, D.C.		50	%		14,938		14,834
	Aviation Business Park	Maryland		50	%		5,677		5,748
	RiversPark I and II(1)	Maryland		25	%		2,197		2,249
							$	47,658	$	47,482
	(1) RiversPark I and RiversPark II are owned through two separate joint ventures.
	On November 12, 2014, our 51% owned unconsolidated joint venture repaid a $48.3 million mortgage loan that encumbered Prosperity Metro Plaza, a two-building, 327,000 square-foot office building located in Merrifield, Virginia. Simultaneously with the repayment, the joint venture entered into a new $50.0 million mortgage loan that has a fixed-interest rate of 3.91%. The new loan requires interest only payments through December 2024, at which time the loan requires principal and interest payments through its maturity date. The loan has a maturity date of December 1, 2029 and is repayable in full without penalty on or after June 1, 2029.
	On September 26, 2014, our 25% owned unconsolidated joint venture amended a $28.0 million mortgage loan that encumbers Rivers Park I and II, a six-building, 308,000 square-foot business park located in Columbia, Maryland. The amended mortgage loan reduced the variable interest rate spread by 60 basis points and reduced the amount of outstanding principal recourse to us from 25% to 10%. The amended loan matures on September 26, 2017 and is repayable in full without penalty at any time during the term of the loan.
	On July 10, 2014, our 50% owned unconsolidated joint venture repaid a $27.9 million mortgage loan that encumbered 1750 H Street, NW, a ten-story, 113,000 square-foot office building located in Washington, D.C. Simultaneously with the repayment, the joint venture entered into a new $32.0 million mortgage loan that has a fixed interest rate of 3.92%, a maturity date of August 1, 2024, and is repayable in full without penalty on or after August 1, 2021. The new loan requires monthly interest-only payments with a constant interest rate over the life of the loan.
	The net assets of our unconsolidated joint ventures consisted of the following (dollars in thousands):
		March 31, 2015				December 31, 2014
	Assets:
	Rental property, net	$	193,201			$	193,533
	Cash and cash equivalents	5,143				4,567
	Other assets	16,514				16,748
	Total assets	214,858				214,848
	Liabilities:
	Mortgage loans(1)	110,000				110,000
	Other liabilities	6,729				7,256
	Total liabilities	116,729				117,256
	Net assets	$	98,129			$	97,592
	(1)	Of the total mortgage debt that encumbers our unconsolidated properties, $2.8 million is recourse to us. We believe the fair value of the potential liability to us under this guaranty is inconsequential as the likelihood of our need to perform under the debt agreement is remote.
	Our share of earnings or losses related to our unconsolidated joint ventures is recorded in our consolidated statements of operations as “Equity in (earnings) losses of affiliates.”
	The following table summarizes the results of operations of our unconsolidated joint ventures, which due to our varying ownership interests in the joint ventures and the varying operations of the joint ventures may or may not be reflective of the amounts recorded in our consolidated statements of operations (dollars in thousands):
		Three Months Ended
		March 31,
		2015				2014
	Total revenues	$	6,167			$	5,752
	Total operating expenses	(2,156		)		(2,226		)
	Net operating income	4,011				3,526
	Depreciation and amortization	(2,249		)		(2,803		)
	Interest expense, net	(973		)		(1,011		)
	Net income (loss)	$	789			$	(288	)
	We earn various fees from several of our joint ventures, which include management fees, leasing commissions and construction management fees. We recognize fees only to the extent of the third party ownership interest in our unconsolidated joint ventures. We recognized fees from our unconsolidated joint ventures of $0.1 million for both the three months ended March 31, 2015 and 2014, which are reflected within “Tenant reimbursements and other revenues” in our consolidated statements of operations.

Dispositions

Dispositions	3 Months Ended
	Mar. 31, 2015
Discontinued Operations and Disposal Groups [Abstract]
Dispositions	Dispositions
	During the second quarter of 2014, we prospectively adopted ASU 2014-08, which states that a component of an entity or a group of components of an entity is required to be reported in discontinued operations only if the disposal represents a strategic shift that has, or will have, a major effect on an entity’s operations and financial results. All other disposed properties will have their operating results reflected within continuing operations on our consolidated statements of operations for all periods presented.
	(a) Disposed or Held-for-Sale Properties within Continuing Operations
	The following table is a summary of completed property dispositions whose operating results are included in continuing operations in our consolidated statements of operations for the periods presented (dollars in thousands):
		Reporting	Disposition Date	Property Type	Square Feet		Net Sale Proceeds
		Segment
	Owings Mills Business Park	Maryland	10/16/14	Business Park	180,475		$	12,417
	Corporate Campus at Ashburn Center	Northern Virginia	6/26/14	Business Park	194,184		39,910
	In accordance with ASU 2014-08, which we prospectively adopted during the second quarter of 2014, the operating results of Corporate Campus at Ashburn Center and Owings Mills Business Park are reflected in continuing operations in our consolidated statements of operations for the three months ended March 31, 2014. For the three months ended March 31, 2015, there were no operating results from disposed properties included in continuing operations. The following table summarizes the aggregate results of operations for the two properties that are included in continuing operations for the three months ended March 31, 2014 (dollars in thousands):
				2014
	Revenues			$	1,465
	Property operating expenses			(548		)
	Depreciation and amortization			(366		)
	Net income from continuing operations			$	551
	(b) Discontinued Operations
	On March 19, 2015, we sold our Richmond, Virginia portfolio, which included Chesterfield Business Center, Hanover Business Center, Park Central, Virginia Technology Center and a three-acre parcel of undeveloped land (the “Richmond Portfolio”) for net proceeds of $53.8 million. In the aggregate, the Richmond Portfolio was comprised of 19 buildings totaling 828,000 square feet. Net proceeds from the sale reflected the prepayment of $3.7 million of mortgage and other indebtedness secured by the properties, including $0.5 million of associated prepayment penalties. The majority of the remaining net proceeds from the sale were used to repay $48.0 million of the outstanding balance under our unsecured revolving credit facility. We recorded a gain on the sale of the portfolio of $0.9 million in the first quarter of 2015. During the first quarter of 2015, we accelerated the amortization of deferred rent abatements and straight-line rents, totaling $0.9 million, and leasing commissions, totaling $1.1 million, which were on the balance sheet of the Richmond Portfolio. The accelerated amortization resulted in an additional $2.0 million of expense during the first quarter of 2015.
	As a result of this sale, we no longer own any properties in the Richmond, Virginia area and have made a strategic shift away from that market. In accordance with ASU 2014-08, the operating results (including the accelerated amortization of deferred rent abatements, straight-line rents and leasing commissions), the loss on debt extinguishment and the gain on sale of the Richmond Portfolio were reflected within discontinued operations for each of the periods presented. In addition to the Richmond Portfolio, all properties sold prior to our adoption of ASU 2014-08 or classified as held-for-sale in previously issued consolidated financial statements prior to our adoption of ASU 2014-08, are classified within discontinued operations.
	The following table is a summary of completed property dispositions whose operating results are reflected as discontinued operations in our consolidated statements of operations for the periods presented (dollars in thousands):
		Reporting	Disposition Date	Property Type	Square Feet		Net Sale Proceeds
		Segment
	Richmond Portfolio	Southern Virginia	3/19/15	Business Park	827,900		$	53,768
	Patrick Center	Maryland	4/16/14	Office	66,269		10,888
	West Park	Maryland	4/2/14	Office	28,333		2,871
	Girard Business Center and Gateway Center	Maryland	1/29/14	Business Park and  Office	341,973		31,616
	We have had, and will have, no continuing involvement with any of our disposed properties subsequent to their disposal. The operations of the disposed properties were not subject to any income based taxes. We did not dispose of or enter into any binding agreements to sell any other properties during the three months ended March 31, 2015 and 2014.
	The following table summarizes the results of operations of properties included in discontinued operations (dollars in thousands):
		Three Months Ended
		March 31,
		2015				2014
	Revenues	$	877			$	1,808
	Loss from operations, before taxes(1)	(975		)		(911		)
	Loss on debt extinguishment	(489		)		—
	Gain on sale of rental property	857				54
	(1)	For the three months ended March 31, 2015, we accelerated $2.0 million of unamortized straight-line rents, deferred rent abatements and leasing commissions related to the sale of the Richmond Portfolio in March 2015. For the three months ended March 31, 2014, we accelerated $1.5 million of unamortized straight-line rents, deferred rent abatements and leasing commissions related to the sale of both Girard Business Center and Gateway Center in January 2014.

Debt

Debt	3 Months Ended
	Mar. 31, 2015
Debt Disclosure [Abstract]
Debt	Debt
	Our borrowings consisted of the following (dollars in thousands):
		March 31,				December 31, 2014(1)
		2015
	Mortgage loans, effective interest rates ranging from 4.40% to 6.01%, maturing at various dates through June 2023(2)	$	303,866			$	308,637
	Unsecured term loan, effective interest rates ranging from LIBOR plus 1.65% to LIBOR plus 2.05%, with staggered maturity dates ranging from October 2018 to October 2020(2)	300,000				300,000
	Unsecured revolving credit facility, effective interest rate of LIBOR plus 1.70%, maturing October 2017(2)	143,000				205,000
		$	746,866			$	813,637
	(1)	Includes five mortgage loans that were repaid with the sale of the Richmond Portfolio on March 19, 2015. At December 31, 2014, the mortgage loans had an aggregate principal balance of $3.5 million and were classified within “Liabilities held-for-sale” on our consolidated balance sheet for December 31, 2014.
	(2)	At March 31, 2015, LIBOR was 0.18%. All references to LIBOR in the condensed consolidated financial statements refer to one-month LIBOR.
	(a) Mortgage Loans
	The following table provides a summary of our mortgage debt at March 31, 2015 and December 31, 2014 (dollars in thousands):
	Encumbered Property		Contractual		Effective			Maturity	March 31,			31-Dec-14
			Interest Rate		Interest			Date	2015
					Rate
	Jackson National Life Loan(1)		5.19%		5.19	%		Aug-15	$	64,640		$	64,943
	440 First Street, NW(2)		LIBOR + 2.50%		LIBOR + 2.50%			May-16	32,216			32,216
	Storey Park(2)		LIBOR + 2.50%		LIBOR + 2.50%			Oct-16	22,000			22,000
	Gateway Centre Manassas Building I		7.35%		5.88	%		November 2016	378			432
	Hillside I and II		5.75%		4.62	%		Dec-16	12,846			12,949
	Redland Corporate Center Buildings II & III		4.20%		4.64	%		Nov-17	65,503			65,816
	840 First Street, NE		5.72%		6.01	%		Jul-20	36,379			36,539
	Battlefield Corporate Center		4.26%		4.4	%		Nov-20	3,651			3,692
	1211 Connecticut Avenue, NW		4.22%		4.47	%		Jul-22	29,548			29,691
	1401 K Street, NW		4.80%		4.93	%		Jun-23	36,705			36,861
					4.75	%	(3)		303,866			305,139
	Unamortized fair value adjustments								(320		)	(370		)
	Principal balance								303,546			304,769
	Richmond Portfolio(4)
	Hanover Business Center Building D		8.88%		6.63	%		Aug-15	—			104
	Chesterfield Business Center Buildings C,D,G and H		8.50%		6.63	%		Sep-15	—			302
	Hanover Business Center Building C		7.88%		6.63	%		Dec-17	—			505
	Chesterfield Business Center Buildings A,B,E and F		7.45%		6.63	%		Jun-21	—			1,674
	Airpark Business Center		7.45%		6.63	%		Jun-21	—			913
									—			3,498
	Total unamortized fair value adjustments - Richmond								—			(73		)
	Total principal balance - Richmond								$	—		$	3,425
	Total principal balance								$	303,546		$	308,194
	(1)	At March 31, 2015, the loan was secured by the following properties: Plaza 500, Van Buren Office Park, Rumsey Center, Snowden Center, Greenbrier Technology Center II and Norfolk Business Center. The terms of the loan allow us to substitute collateral, as long as certain debt-service coverage and loan-to-value ratios are maintained, or to prepay a portion of the loan, with a prepayment penalty, subject to a debt-service yield.
	(2)	At March 31, 2015, LIBOR was 0.18%.
	(3)	Weighted average interest rate on total mortgage debt.
	(4)	The mortgage loans and unamortized fair value adjustments that encumbered properties within the Richmond Portfolio were classified within “Liabilities held-for-sale” on our consolidated balance sheet at December 31, 2014. The loans were prepaid upon the sale of the Richmond Portfolio on March 19, 2015.
	Land Loan
	On October 16, 2014, our 97% owned consolidated joint venture that owns Storey Park repaid a $22.0 million loan that encumbered the Storey Park land and was subject to a 5.0% interest rate floor. Simultaneously with the repayment, the joint venture entered into a new $22.0 million land loan with a variable interest rate of LIBOR plus 2.50%. The new loan matures on October 16, 2016, with a one-year extension at our option, and is repayable in full without penalty at any time during the term of the loan. Per the terms of the loan agreement, $6.0 million of the outstanding principal balance and all of the outstanding accrued interest is recourse to us. As of March 31, 2015, we were in compliance with all the financial covenants of the Storey Park land loan.
	Construction Loan
	On June 5, 2013, we entered into a construction loan (the “Construction Loan”) that is collateralized by our 440 First Street, NW property, which underwent a major redevelopment that was substantially completed in October 2013. The Construction Loan has a borrowing capacity of up to $43.5 million, of which we initially borrowed $21.7 million in 2013 and borrowed an additional $10.5 million in 2014. The Construction Loan has a variable interest rate of LIBOR plus a spread of 2.5% and matures in May 2016, with two one-year extension options at our discretion. We can repay all or a portion of the Construction Loan, without penalty, at any time during the term of the loan. At March 31, 2015, per the terms of the loan agreement, 50% of the outstanding principal balance and all of the outstanding accrued interest were recourse to us. The percentage of outstanding principal balance that is recourse to us can be reduced upon the property achieving certain operating thresholds. As of March 31, 2015, we were in compliance with all the financial covenants of the Construction Loan.
	(b) Unsecured Term Loan
	The table below shows the outstanding balances and the interest rates of the three tranches of the $300.0 million unsecured term loan at March 31, 2015 (dollars in thousands):
		Maturity Date		Amount				Interest Rate(1)
	Tranche A	October 2018		$	100,000			LIBOR, plus 165 basis points
	Tranche B	October 2019		100,000				LIBOR, plus 180 basis points
	Tranche C	October 2020		100,000				LIBOR, plus 205 basis points
				$	300,000
	(1)	At March 31, 2015, LIBOR was 0.18%. The interest rate spread is subject to change based on our maximum total indebtedness ratio. For more information, see note 8(e) Debt – Financial Covenants.
	The term loan agreement contains various restrictive covenants substantially identical to those contained in our unsecured revolving credit facility, including with respect to liens, indebtedness, investments, distributions, mergers and asset sales. In addition, the agreement requires that we satisfy certain financial covenants that are also substantially identical to those contained in our unsecured revolving credit facility. The agreement also includes customary events of default, the occurrence of which, following any applicable cure period, would permit the lenders to, among other things, declare the principal, accrued interest and other obligations of our Company under the agreement to be immediately due and payable. As of March 31, 2015, we were in compliance with all the financial covenants of the unsecured term loan.
	(c) Unsecured Revolving Credit Facility
	During the first quarter of 2015, we borrowed $13.0 million under the unsecured revolving credit facility which was used for general corporate purposes. During the first quarter of 2015, we repaid $75.0 million of the outstanding balance under the unsecured revolving credit facility with our portion of the proceeds from the prepayment of the America’s Square mezzanine loan and the sale of the Richmond Portfolio. For the three months ended March 31, 2015, our weighted average borrowings under the unsecured revolving credit facility were $193.5 million, with a weighted average interest rate of 1.9%, compared with weighted average borrowings of $97.1 million, with a weighted average interest rate of 1.7%, for the three months ended March 31, 2014. Our maximum outstanding borrowings were $218.0 million and $112.0 million for the three months ended March 31, 2015 and 2014, respectively. At March 31, 2015, outstanding borrowings under the unsecured revolving credit facility were $143.0 million with a weighted average interest rate of 1.9%. At March 31, 2015, LIBOR was 0.18% and the applicable spread on our unsecured revolving credit facility was 170 basis points. The available capacity under the unsecured revolving credit facility was $138.2 million as of the date of this filing. We are required to pay an annual commitment fee of 0.25% based on the amount of unused capacity under the unsecured revolving credit facility. As of March 31, 2015, we were in compliance with all the financial covenants of the unsecured revolving credit facility. For more information, see note 8(e) Debt – Financial Covenants.
	(d) Interest Rate Swap Agreements
	At March 31, 2015, we had eleven interest rate swap agreements outstanding that collectively fixed LIBOR, at a weighted average interest rate of 1.5%, on $300.0 million of our variable rate debt. See note 9, Derivative Instruments, for more information about our interest rate swap agreements.
	(e) Financial Covenants
	Our outstanding corporate debt agreements contain specific financial covenants that may impact future financing decisions made by us or may be impacted by a decline in operations. These covenants relate to our allowable leverage, minimum tangible net worth, fixed charge coverage and other financial metrics. As of March 31, 2015, we were in compliance with the covenants of our unsecured term loan and unsecured revolving credit facility and any such financial covenants of our mortgage debt (including the Construction Loan and the Storey Park land loan).
	Our continued ability to borrow under the unsecured revolving credit facility is subject to compliance with financial and operating covenants, and a failure to comply with any of these covenants could result in a default under the credit facility. These debt agreements also contain cross-default provisions that would be triggered if we were in default under other loans, including mortgage loans, in excess of certain amounts. In the event of a default, the lenders could accelerate the timing of payments under the debt obligations and we may be required to repay such debt with capital from other sources, which may not be available on attractive terms, or at all, which would have a material adverse effect on our liquidity, financial condition, results of operations and ability to make distributions to our shareholders.
	Our unsecured revolving credit facility and unsecured term loan are subject to interest rate spreads that float based on the quarterly measurement of our maximum consolidated total indebtedness to gross asset value ratio. Based on our leverage ratio at March 31, 2015, the applicable interest rate spreads on the unsecured revolving credit facility and the unsecured term loan will be unchanged.

Derivative_Instruments

Derivative Instruments	3 Months Ended
	Mar. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments	Derivative Instruments
	We are exposed to certain risks arising from business operations and economic factors. We use derivative financial instruments to manage exposures that arise from business activities in which our future exposure to interest rate fluctuations is unknown. The objective in the use of an interest rate derivative is to add stability to interest expenses and manage exposure to interest rate changes. We do not use derivatives for trading or speculative purposes and we intend to enter into derivative agreements only with counterparties that we believe have a strong credit rating to mitigate the risk of counterparty default or insolvency. No hedging activity can completely insulate us from the risks associated with changes in interest rates. Moreover, interest rate hedging could fail to protect us or adversely affect us because, among other things:
	•	available interest rate hedging may not correspond directly with the interest rate risk for which we seek protection;
	•	the duration of the hedge may not match the duration of the related liability;
	•	the party owing money in the hedging transaction may default on its obligation to pay; and
	•	the credit quality of the party owing money on the hedge may be downgraded to such an extent that it impairs our ability to sell or assign its side of the hedging transaction.
	We enter into interest rate swap agreements to hedge our exposure on our variable rate debt against fluctuations in prevailing interest rates. The interest rate swap agreements fix LIBOR to a specified interest rate; however, the swap agreements do not affect the contractual spreads associated with each variable debt instrument’s applicable interest rate.
	At March 31, 2015, we had eleven interest rate swap agreements outstanding that collectively fixed LIBOR, at a weighted average interest rate of 1.5%, on $300.0 million of our variable rate debt. Our interest rate swap agreements are summarized below (dollars in thousands):
	Maturity Date		Notional		Interest Rate	Fixed LIBOR
			Amount		Contractual	Interest Rate
					Component
	Jul-16		$	35,000	LIBOR	1.754	%
	Jul-16		25,000		LIBOR	1.763	%
	Jul-17		30,000		LIBOR	2.093	%
	Jul-17		30,000		LIBOR	2.093	%
	Jul-17		25,000		LIBOR	1.129	%
	Jul-17		12,500		LIBOR	1.129	%
	Jul-17		50,000		LIBOR	0.955	%
	Jul-18		12,500		LIBOR	1.383	%
	Jul-18		30,000		LIBOR	1.66	%
	Jul-18		25,000		LIBOR	1.394	%
	Jul-18		25,000		LIBOR	1.135	%
	Total/Weighted Average		$	300,000		1.505	%
	Our interest rate swap agreements are designated as cash flow hedges and we record the effective portion of any unrealized gains associated with the change in fair value of the swap agreements within “Accumulated other comprehensive loss” and “Prepaid expenses and other assets” and the effective portion of any unrealized losses within “Accumulated other comprehensive loss” and “Accounts payable and other liabilities” on our consolidated balance sheets. We record our proportionate share of any unrealized gains or losses on our cash flow hedges associated with our unconsolidated joint ventures within “Accumulated other comprehensive loss” and “Investment in affiliates” on our consolidated balance sheets. We record any gains or losses incurred as a result of each interest rate swap agreement’s fixed rate deviating from our respective loan’s contractual rate within “Interest expense” in our consolidated statements of operations. We did not have any material ineffectiveness associated with our cash flow hedges during the three months ended March 31, 2015 and 2014.
	Amounts reported in accumulated other comprehensive loss related to derivatives will be reclassified to “Interest expense” on our consolidated statements of operations as interest payments are made on our variable-rate debt. We reclassified accumulated other comprehensive loss as an increase to interest expense of $1.0 million for both the three months ended March 31, 2015 and 2014. As of March 31, 2015, we estimated that $4.3 million of our accumulated other comprehensive loss will be reclassified as an increase to interest expense over the following twelve months.

Fair_Value_Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements
	Our application of GAAP outlines a valuation framework and creates a fair value hierarchy, which distinguishes between assumptions based on market data (observable inputs) and a reporting entity’s own assumptions about market data (unobservable inputs). The required disclosures increase the consistency and comparability of fair value measurements and the related disclosures. Fair value is identified, under the standard, as the price that would be received to sell an asset or paid to transfer a liability between willing third parties at the measurement date (an exit price). In accordance with GAAP, certain assets and liabilities must be measured at fair value, and we provide the necessary disclosures that are required for items measured at fair value as outlined in the accounting requirements regarding fair value.
	Financial assets and liabilities, as well as those non-financial assets and liabilities requiring fair value measurement, are measured using inputs from three levels of the fair value hierarchy.
	The three levels are as follows:
	Level 1 - Inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that we have the ability to access at the measurement date. An active market is defined as a market in which transactions for the assets or liabilities occur with sufficient frequency and volume to provide pricing information on an ongoing basis.
	Level 2 - Inputs include quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active (markets with few transactions), inputs other than quoted prices that are observable for the asset or liability (i.e., interest rates, yield curves, etc.), and inputs derived principally from or corroborated by observable market data correlation or other means (market corroborated inputs).
	Level 3 - Unobservable inputs, only used to the extent that observable inputs are not available, reflect our assumptions about the pricing of an asset or liability.
	In accordance with accounting provisions and the fair value hierarchy described above, the following table shows the fair value of our consolidated assets and liabilities that are measured on a non-recurring and recurring basis as of March 31, 2015 and December 31, 2014 (dollars in thousands):
		Balance at		Level 1		Level 2		Level 3
		March 31, 2015
	Recurring Measurements:
	Derivative instrument-swap liabilities	$	4,518	$	—	$	4,518	$	—
		Balance at		Level 1		Level 2		Level 3
		December 31, 2014
	Recurring Measurements:
	Derivative instrument-swap assets	$	133	$	—	$	133	$	—
	Derivative instrument-swap liabilities	3,569		—		3,569		—
	We did not re-measure or complete any transactions involving non-financial assets or non-financial liabilities that are measured at fair value on a recurring basis during the three months ended March 31, 2015 and 2014. Also, no transfers into or out of fair value measurement levels for assets or liabilities that are measured on a recurring basis occurred during the three months ended March 31, 2015 and 2014.
	Interest Rate Derivatives
	At March 31, 2015, we had hedged $300.0 million of our variable rate debt through eleven interest rate swap agreements. See note 9, Derivative Instruments, for more information about our interest rate swap agreements.
	The interest rate derivatives are fair valued based on prevailing market yield curves on the measurement date and also incorporate credit valuation adjustments to appropriately reflect both our own nonperformance risk and the respective counterparty’s nonperformance risk in the fair value measurements. In adjusting the fair value of our derivative contracts for the effect of nonperformance risk, we have considered the impact of netting any applicable credit enhancements, such as collateral postings, thresholds, mutual inputs and guarantees. We use a third party to assist in valuing our interest rate swap agreements. A daily “snapshot” of the market is taken to obtain close of business rates. The snapshot includes over 7,500 rates including LIBOR fixings, Eurodollar futures, swap rates, exchange rates, treasuries, etc. This market data is obtained via direct feeds from Bloomberg and Reuters and from Inter-Dealer Brokers. The selected rates are compared to their historical values. Any rate that has changed by more than normal mean and related standard deviation would be considered an outlier and flagged for further investigation. The rates are then compiled through a valuation process that generates daily valuations, which are used to value our interest rate swap agreements. Our interest rate swap derivatives are effective cash flow hedges and the effective portion of the change in fair value is recorded in the equity section of our consolidated balance sheets as “Accumulated other comprehensive loss.”
	Financial Instruments
	The carrying amounts of cash equivalents, accounts and other receivables, accounts payable and other liabilities, with the exception of any items listed above, approximate their fair values due to their short-term maturities. We determine the fair value of our notes receivable and debt instruments by discounting future contractual principal and interest payments using prevailing market rates for securities with similar terms and characteristics at the balance sheet date. We deem the fair value measurement of our debt instruments as a Level 2 measurement as we use quoted interest rates for similar debt instruments to value our debt instruments. We also use quoted market interest rates for similar notes to value our notes receivable, which we consider a Level 2 measurement as we do not believe notes receivable trade in an active market.
	The carrying amount and estimated fair value of our notes receivable and debt instruments are as follows (amounts in thousands):
		March 31, 2015				December 31, 2014
		Carrying		Fair		Carrying		Fair
		Value		Value		Value		Value
	Financial Assets:
	Notes receivable(1)	$	34,000	$	34,000	$	63,679	$	63,720
	Financial Liabilities:
	Mortgage debt(2)	$	303,866	$	299,042	$	308,637	$	292,882
	Unsecured term loan	300,000		300,000		300,000		300,000
	Unsecured revolving credit facility	143,000		143,000		205,000		205,000
	Total	$	746,866	$	742,042	$	813,637	$	797,882
	(1)	The principal amount of our notes receivable was $34.0 million and $63.7 million at March 31, 2015 and December 31, 2014, respectively.
		On February 24, 2015, the owners of America’s Square, a 461,000 square foot office complex located in Washington, D.C., prepaid a mezzanine loan, which had an outstanding $29.7 million balance of the $30.0 million mezzanine loan that we provided them in April 2011.
	(2)	Includes five mortgage loans that were repaid with the sale of the Richmond Portfolio on March 19, 2015. At December 31, 2014, the mortgage loans had an aggregate principal balance of $3.5 million and were classified within “Liabilities held-for-sale” on our consolidated balance sheet for December 31, 2014.

Equity

Equity	3 Months Ended
	Mar. 31, 2015
Equity [Abstract]
Equity	Equity
	On January 27, 2015, we declared a dividend of $0.15 per common share, equating to an annualized dividend of $0.60 per common share. The dividend was paid on February 17, 2015 to common shareholders of record as of February 10, 2015. We also declared a dividend of $0.484375 per share on our Series A Preferred Shares. The dividend was paid on February 17, 2015 to preferred shareholders of record as of February 10, 2015. Dividends on all non-vested share awards are recorded as a reduction of shareholders’ equity. For each dividend paid by us on our common and preferred shares, the Operating Partnership distributes an equivalent distribution on our common and preferred Operating Partnership units, respectively.
	On April 28, 2015, we declared a dividend of $0.15 per common share, equating to an annualized dividend of $0.60 per common share. The dividend will be paid on May 15, 2015 to common shareholders of record as of May 8, 2015. We also declared a dividend of $0.484375 per share on our Series A Preferred Shares. The dividend will be paid on May 15, 2015 to preferred shareholders of record as of May 8, 2015.
	Our unsecured revolving credit facility, unsecured term loan, the Construction Loan and the Storey Park land loan contain certain restrictions that include, among other things, requirements to maintain specified coverage ratios and other financial covenants, which may limit our ability to make distributions to our common and preferred shareholders. Further, distributions with respect to our common shares are subject to our ability to first satisfy our obligations to pay distributions to the holders of our Series A Preferred Shares.
	As a result of the redemption feature of the Operating Partnership units, the noncontrolling interests associated with the Operating Partnership are recorded outside of permanent equity. Our equity and redeemable noncontrolling interests are as follows (dollars in thousands):
		First			Non-redeemable			Total Equity			Redeemable
		Potomac			noncontrolling						noncontrolling
		Realty Trust			interests						interests
	Balance at December 31, 2014	$	710,007		$	898		$	710,905		$	33,332
	Net income (loss)	604			—			604			(112		)
	Changes in ownership, net	1,281			(96		)	1,185			(581		)
	Distributions to owners	(11,902		)	—			(11,902		)	(395		)
	Other comprehensive loss	(1,030		)	—			(1,030		)	(46		)
	Balance at March 31, 2015	$	698,960		$	802		$	699,762		$	32,198
		First			Non-redeemable			Total Equity			Redeemable
		Potomac			noncontrolling						noncontrolling
		Realty Trust			interests						interests
	Balance at December 31, 2013	$	738,510		$	781		$	739,291		$	33,221
	Net loss	(1,248		)	—			(1,248		)	(195		)
	Changes in ownership, net	(1,502		)	89			(1,413		)	2,067
	Distributions to owners	(11,889		)	—			(11,889		)	(393		)
	Other comprehensive income	168			—			168			7
	Balance at March 31, 2014	$	724,039		$	870		$	724,909		$	34,707
	A summary of our accumulated other comprehensive loss is as follows (dollars in thousands):
		2015			2014
	Beginning balance at January 1,	$	(3,268	)	$	(3,836	)
	Net unrealized (loss) gain on derivative instruments	(1,076		)	175
	Net loss (gain) attributable to noncontrolling interests	46			(7		)
	Ending balance at March 31,	$	(4,298	)	$	(3,668	)

Noncontrolling_Interests

Noncontrolling Interests	3 Months Ended
	Mar. 31, 2015
Noncontrolling Interest [Abstract]
Noncontrolling Interests	Noncontrolling Interests
	(a) Noncontrolling Interests in the Operating Partnership
	Noncontrolling interests relate to the common interests in the Operating Partnership not owned by us. Interests in the Operating Partnership are owned by limited partners who contributed buildings and other assets to the Operating Partnership in exchange for common Operating Partnership units. Limited partners have the right to tender their units for redemption in exchange for, at our option, our common shares on a one-for-one basis or cash based on the fair value of our common shares at the date of redemption. Unitholders receive a distribution per unit equivalent to the dividend per common share. Differences between amounts paid to redeem noncontrolling interests and their carrying values are charged or credited to equity. As a result of the redemption feature of the Operating Partnership units, the noncontrolling interests are recorded outside of permanent equity.
	Noncontrolling interests are presented at the greater of their fair value or their cost basis, which is comprised of their fair value at issuance, subsequently adjusted for the noncontrolling interests’ share of net income or losses available to common shareholders, other comprehensive income or losses, distributions received or additional contributions. We account for issuances of common Operating Partnership units individually, which could result in some portion of our noncontrolling interests being carried at fair value with the remainder being carried at historical cost. Based on the closing price of our common shares at March 31, 2015, the cost to acquire, through cash purchase or issuance of our common shares, all of the outstanding common Operating Partnership units not owned by us would be approximately $31.3 million. At March 31, 2015 and December 31, 2014, we recorded adjustments of $4.2 million and $4.7 million, respectively, to present certain common Operating Partnership units at the greater of their carrying value or redemption value.
	At March 31, 2015, 2,630,577 of the total common Operating Partnership units, or 4.3%, were not owned by us. There were no common Operating Partnership units redeemed for common shares or cash during the three months ended March 31, 2015. During the first quarter of 2014, we issued 3,125 common Operating Partnership units to the seller of 840 First Street, NE to satisfy a contingent consideration obligation.
	(b) Noncontrolling Interests in a Consolidated Partnership
	When we are deemed to have a controlling interest in a partially-owned entity, we will consolidate all of the entity’s assets, liabilities and operating results within our condensed consolidated financial statements. The net assets contributed to the consolidated entity by the third party, if any, will be reflected within permanent equity in our consolidated balance sheets to the extent they are not mandatorily redeemable. The amount will be recorded based on the third party’s initial investment in the consolidated entity and will be adjusted to reflect the third party’s share of earnings or losses in the consolidated entity and any distributions received or additional contributions made by the third party. The earnings or losses from the entity attributable to the third party are recorded as a component of “Net loss attributable to noncontrolling interests” in our consolidated statements of operations.
	On August 4, 2011, we formed a joint venture, in which we have a 97% interest, with an affiliate of Perseus Realty, LLC to acquire Storey Park in our Washington, D.C. reporting segment. At the time, the site was leased to Greyhound, which subsequently relocated its operations. Greyhound’s lease expired on August 31, 2013, at which time the property was placed into development. The joint venture anticipates developing a mixed-use project on the 1.6 acre site, which can accommodate up to 712,000 square feet. At March 31, 2015, our total investment in the development project was $56.0 million, which included the original cost basis of the property of $43.3 million. The majority of the costs in excess of the original cost basis relate to capitalized architectural fees and site preparation costs. We are currently exploring our options related to this property; however, until a definitive plan for the property has been reached and we begin significant development activities, we cannot determine the total cost of the project or the anticipated completion date.

ShareBased_Payments

Share-Based Payments	3 Months Ended
	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Payments	Share-Based Payments
	We record costs related to our share-based compensation based on the grant-date fair value calculated in accordance with GAAP. We recognize share-based compensation costs on a straight-line basis over the requisite service period for each award and these costs are recorded within “General and administrative expense” or “Property operating expense” in our consolidated statements of operations based on the employee’s job function.
	Stock Options Summary
	During the three months ended March 31, 2015, we issued 119,500 stock options to our non-officer employees. The stock options vest 25% on the first anniversary of the date of grant and 6.25% in each subsequent calendar quarter. The award described above has a 10-year contractual life. We recognized compensation expense associated with stock option awards of $118 thousand and $137 thousand during the three months ended March 31, 2015 and 2014, respectively.
	A summary of our stock option activity during the three months ended March 31 is presented below:
		Options		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term	Aggregate Intrinsic Value
	Outstanding at December 31, 2014	1,051,359		$	15.33	6.3 years	$	181,352
	Granted	119,500		12.48
	Exercised	(2,000	)	9.3
	Expired	(59,000	)	22.44
	Forfeited	(49,771	)	14.48
	Outstanding at March 31, 2015	1,060,088		$	14.67	6.8 years	$	107,523
	Exercisable at March 31, 2015	516,839		$	15.52	5.8 years	$	87,260
	Options expected to vest, subsequent to March 31, 2015	507,651		$	13.97	7.6 years	$	17,602
	As of March 31, 2015, we had $1.4 million of unrecognized compensation cost, net of estimated forfeitures, related to stock option awards. We anticipate this cost will be recognized over a weighted-average period of approximately 4.0 years. We calculate the grant date fair value of option awards using a Black-Scholes option-pricing model. Expected volatility is based on an assessment of our realized volatility over the preceding period that is equivalent to the award’s expected life, which in our opinion, gives an accurate indication of future volatility. The expected term represents the period of time the options are anticipated to remain outstanding as well as our historical experience for groupings of employees that have similar behavior and are considered separately for valuation purposes. The risk-free rate is based on the U.S. Treasury rate at the time of grant for instruments of similar terms.
	The weighted average assumptions used in the fair value determination of stock options granted to employees during the three months ended March 31, 2015 are summarized as follows:
	Risk-free interest rate	1.61	%
	Expected volatility	29.16	%
	Expected dividend yield	4.79	%
	Weighted average expected life of options	5 years
	The weighted average grant date fair value of the stock options issued during the three months ended March 31, 2015 was $1.96 per share.
	Option Exercises
	We received approximately $19 thousand and $79 thousand of proceeds from stock option exercises during the three months ended March 31, 2015 and 2014, respectively. Shares issued as a result of stock option exercises are provided by the issuance of new shares. The total intrinsic value of options exercised during the three months ended March 31, 2015 and 2014 was $5 thousand and $18 thousand, respectively.
	Non-Vested Share Awards
	We issue non-vested common share awards that either vest over a specific time period that is identified at the time of issuance or vest upon the achievement of specific performance goals that are identified at the time of issuance. We issue new common shares, subject to restrictions, upon each grant of non-vested common share awards. In February 2015, we granted a total of 121,380 non-vested common shares to our officers. The awards will vest ratably on the date of issuance over a three-year term.
	We recognized $0.6 million and $0.7 million of compensation expense associated with our non-vested common share awards during the three months ended March 31, 2015 and 2014, respectively. Dividends on all non-vested common share awards are recorded as a reduction of equity. We apply the two-class method for determining EPS as our outstanding non-vested common shares with non-forfeitable dividend rights are considered participating securities. Our excess of dividends over earnings related to participating securities are shown as a reduction in net income or loss attributable to common shareholders in our computation of EPS.
	A summary of our non-vested common share awards at March 31, 2015 is as follows:
		Non-vested		Weighted
		Common		Average Grant
		Shares		Date Fair Value
	Non-vested at December 31, 2014	623,421		$	13.16
	Granted	121,380		12.11
	Vested	(106,300	)	13.97
	Expired	(22,260	)	8.42
	Forfeited	(154,626	)	13.42
	Non-vested at March 31, 2015	461,615		$	12.83
	We value our non-vested time-based share awards at the grant date fair value, which is the market price of our common shares. As of March 31, 2015, we had $4.0 million of unrecognized compensation cost related to non-vested common shares. We anticipate this cost will be recognized over a weighted-average period of 2.3 years.

Segment_Information

Segment Information	3 Months Ended
	Mar. 31, 2015
Segment Reporting [Abstract]
Segment Information	Segment Information
	Our reportable segments consist of four distinct reporting and operational segments within the greater Washington, D.C. region in which we operate: Washington, D.C., Maryland, Northern Virginia and Southern Virginia. We evaluate the performance of our segments based on the operating results of the properties located within each segment, which excludes large non-recurring gains and losses, gains or losses from sale of rental property, interest expense, general and administrative costs, acquisition costs or any other indirect corporate expense to the segments. In addition, the segments do not have significant non-cash items other than straight-line and deferred market rent amortization reported in their operating results. There are no inter-segment sales or transfers recorded between segments.
	The results of operations of our four reporting segments for the three months ended March 31, 2015 and 2014 are as follows (dollars in thousands):
		Three Months Ended March 31, 2015
		Washington, D.C.			Maryland			Northern Virginia			Southern Virginia			Consolidated
	Number of buildings(1)	6			38			49			19			112
	Square feet(1)	916,686			1,999,300			3,021,299			2,024,003			7,961,288
	Total revenues	$	11,032		$	11,705		$	14,114		$	6,998		$	43,849
	Property operating expense	(3,139		)	(4,018		)	(4,064		)	(1,892		)	(13,113		)
	Real estate taxes and insurance	(2,023		)	(891		)	(1,549		)	(579		)	(5,042		)
	Total property operating income	$	5,870		$	6,796		$	8,501		$	4,527		25,694
	Depreciation and amortization expense													(16,335		)
	General and administrative													(5,526		)
	Other expenses													(2,734		)
	Loss from discontinued operations													(607		)
	Net income													$	492
	Total assets(2)(3)	$	503,651		$	358,772		$	444,596		$	167,979		$	1,534,448
	Capital expenditures(4)	$	3,436		$	2,164		$	10,843		$	2,490		$	19,242
		Three Months Ended March 31, 2014
		Washington, D.C.			Maryland			Northern Virginia			Southern Virginia			Consolidated
	Number of buildings(1)(5)	4			44			51			38			137
	Square feet(1)(5)	522,560			2,274,813			3,086,550			2,851,465			8,735,388
	Total revenues	$	6,940		$	11,645		$	13,666		$	7,112		$	39,363
	Property operating expense	(1,987		)	(3,946		)	(3,976		)	(2,129		)	(12,038		)
	Real estate taxes and insurance	(1,054		)	(1,004		)	(1,524		)	(550		)	(4,132		)
	Total property operating income	$	3,899		$	6,695		$	8,166		$	4,433		23,193
	Depreciation and amortization expense													(14,310		)
	General and administrative													(5,196		)
	Acquisition costs													(68		)
	Other expenses													(4,205		)
	Loss from discontinued operations													(857		)
	Net loss													$	(1,443	)
	Total assets(2)(3)	$	343,804		$	393,919		$	421,556		$	230,384		$	1,481,336
	Capital expenditures(4)	$	6,481		$	2,390		$	822		$	1,423		$	11,393
	(1)	Excludes Storey Park from our Washington, D.C. reporting segment, which was placed in development in the third quarter of 2013.
	(2)	Total assets include our investment in properties that are owned through joint ventures that are not consolidated within our condensed consolidated financial statements. For more information on our unconsolidated investments, including location within our reportable segments, see note 6, Investment in Affiliates.
	(3)	Corporate assets not allocated to any of our reportable segments totaled $59,450 and $91,673 at March 31, 2015 and 2014, respectively.
	(4)	Capital expenditures for corporate assets not allocated to any of our reportable segments totaled $309 and $277 for the three months ended March 31, 2015 and 2014, respectively.
	(5)	Includes occupied space at 440 First Street, NW in our Washington, D.C. reporting segment, which was substantially completed in the third quarter of 2013. In October 2014, the property was placed in service.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation
	Our unaudited condensed consolidated financial statements include our accounts and the accounts of our Operating Partnership and the subsidiaries in which we or our Operating Partnership has a controlling interest, which includes First Potomac Management LLC, a wholly-owned subsidiary that manages the majority of our properties. All intercompany balances and transactions have been eliminated in consolidation.
	We have condensed or omitted certain information and note disclosures normally included in financial statements presented in accordance with U.S. generally accepted accounting principles (“GAAP”) in the accompanying unaudited condensed consolidated financial statements. We believe the disclosures made are adequate to prevent the information presented from being misleading. However, the unaudited condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto included in our annual report on Form 10-K for the year ended December 31, 2014 and as updated from time to time in other filings with the SEC.
	In our opinion, the accompanying unaudited condensed consolidated financial statements reflect all adjustments, consisting of normal recurring adjustments and accruals necessary to present fairly our financial position as of March 31, 2015 and the results of our operations, our comprehensive loss and our cash flows for the three months ended March 31, 2015 and 2014. Interim results are not necessarily indicative of full-year performance due, in part, to the timing of transactions and the impact of acquisitions and dispositions throughout the year as well as the seasonality of certain operating expenses such as utilities expense and snow and ice removal costs.
Use of Estimates	Use of Estimates
	The preparation of condensed consolidated financial statements in conformity with GAAP requires our management team to make a number of estimates and assumptions relating to the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the unaudited condensed consolidated financial statements and the reported amounts of revenues and expenses during the period. Estimates include the amount of accounts receivable that may be uncollectible; recoverability of notes receivable, future cash flows, discount and capitalization rate assumptions used to fair value acquired properties and to test impairment of certain long-lived assets and goodwill; derivative valuations; market lease rates, lease-up periods, leasing and tenant improvement costs used to fair value intangible assets acquired and probability weighted cash flow analysis used to fair value contingent liabilities. Actual results could differ from those estimates.
Rental Property	Rental Property
	Rental property is initially recorded at fair value, if acquired in a business combination, or initial cost when constructed or acquired in an asset purchase. Improvements and replacements are capitalized at cost when they extend the useful life, increase capacity or improve the efficiency of the asset. Repairs and maintenance are charged to expense when incurred. Depreciation and amortization are recorded on a straight-line basis over the estimated useful lives of the assets. The estimated useful lives of our assets, by class, are as follows:
	Buildings	39 years
	Building improvements	5 to 20 years
	Furniture, fixtures and equipment	5 to 15 years
	Lease related intangible assets	The term of the related lease
	Tenant improvements	Shorter of the useful life of the asset or the term of the related lease
	We regularly review market conditions for possible impairment of a property’s carrying value. When circumstances such as adverse market conditions, changes in management’s intended holding period or potential sale to a third party indicate a possible impairment of the carrying value of a property, an impairment analysis is performed. We assess potential impairments based on an estimate of the future undiscounted cash flows (excluding interest charges) expected to result from the property’s use and eventual disposition. This estimate is based on projections of future revenues, expenses, capital improvement costs to maintain the operating capacity, expected holding periods and capitalization rates. These cash flows consider factors such as expected market trends and leasing prospects, as well as the effects of leasing demand, competition and other factors. If impairment exists due to the inability to recover the carrying value of a real estate investment based on forecasted undiscounted cash flows, an impairment loss is recorded to the extent that the carrying value exceeds the estimated fair value of the property. Further, we will record an impairment loss if we expect to dispose of a property, in the near term, at a price below carrying value. In such an event, we will record an impairment loss based on the difference between a property’s carrying value and its projected sales price less any estimated costs to sell.
	We will classify a building as held-for-sale in accordance with GAAP in the period in which we have made the decision to dispose of the building, our Board of Trustees or a designated delegate has approved the sale, there is a high likelihood a binding agreement to purchase the property will be signed under which the buyer will be required to commit a significant amount of nonrefundable cash and no significant financing contingencies exist that could cause the transaction not to be completed in a timely manner. We will cease recording depreciation on a building once it has been classified as held-for-sale. In the second quarter of 2014, we prospectively adopted Accounting Standards Update 2014-08, Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity (“ASU 2014-08”), which impacts the presentation of operations and gains or losses from disposed properties and properties classified as held-for-sale. ASU 2014-08 states that a disposal of a component of an entity or a group of components of an entity is required to be reported in discontinued operations only if the disposal represents a strategic shift that has, or will have, a major effect on an entity’s operations or financial results. The operations of all properties that were sold prior to the adoption of ASU 2014-08, two properties that were classified as held-for-sale in previously issued financial statements prior to our adoption of ASU 2014-08 (West Park and Patrick Center) and were subsequently sold, as well as the Richmond Portfolio (as defined below), are reflected within discontinued operations in our consolidated statements of operations for all periods presented.
	If the building does not qualify as a discontinued operation under ASU 2014-08, we will classify the building's operating results, together with any impairment charges and any gains or losses on the sale of the building, in continuing operations for all periods presented in our consolidated statements of operations. We will classify the assets and liabilities related to the building as held-for-sale in our consolidated balance sheet for the period the held-for-sale criteria were met.
	If the building does qualify as a discontinued operation under ASU 2014-08, we will classify the building's operating results, together with any impairment charges and any gains or losses on the sale of the building, in discontinued operations in our consolidated statements of operations for all periods presented and classify the assets and liabilities related to the building as held-for-sale in our consolidated balance sheets for the periods presented. Interest expense is reclassified to discontinued operations only to the extent the disposed or held-for-sale property is secured by specific mortgage debt and the mortgage debt will not be assigned to another property owned by us after the disposition.
	We recognize the fair value, if sufficient information exists to reasonably estimate the fair value, of any liability for conditional asset retirement obligations when assumed or incurred, which is generally upon acquisition, construction, development or redevelopment and/or through the normal operation of the asset.
	We capitalize interest costs incurred on qualifying expenditures for real estate assets under development or redevelopment, which include our investments in assets owned through unconsolidated joint ventures that are under development or redevelopment, while being readied for their intended use in accordance with accounting requirements regarding capitalization of interest. We will capitalize interest when qualifying expenditures for the asset have been made, activities necessary to get the asset ready for its intended use are in progress and interest costs are being incurred. Capitalized interest also includes interest associated with expenditures incurred to acquire developable land while development activities are in progress. We also capitalize direct compensation costs of our construction personnel who manage the development and redevelopment projects, but only to the extent the employee’s time can be allocated to a project. Any portion of construction management costs not directly attributable to a specific project are recognized as general and administrative expense in the period incurred. We do not capitalize any other general and administrative costs such as office supplies, office rent expense or an overhead allocation to our development or redevelopment projects. Capitalized compensation costs were immaterial for the three months ended March 31, 2015 and 2014. Capitalization of interest ends when the asset is substantially complete and ready for its intended use, but no later than one year from completion of major construction activity, if the property is not occupied. We place redevelopment and development assets into service at this time and commence depreciation upon the substantial completion of tenant improvements and the recognition of revenue. Capitalized interest is depreciated over the useful life of the underlying assets, commencing when those assets are placed into service.
Notes Receivable	Notes Receivable
	We provide loans to the owners of real estate properties, which can be collateralized by interest in the real estate property. We record these loans as “Notes receivable, net” in our consolidated balance sheets. The loans are recorded net of any discount or issuance costs, which are amortized over the life of the respective note receivable using the effective interest method. We record interest earned from notes receivable and amortization of any discount costs or issuance costs within “Interest and other income” in our consolidated statements of operations.
	We will establish a provision for anticipated credit losses associated with our notes receivable when we anticipate that we may be unable to collect any contractually due amounts. This determination is based upon such factors as delinquencies, loss experience, collateral quality and current economic or borrower conditions. Our collectability of our notes receivable may be adversely impacted by the financial stability of the Washington, D.C. region and the ability of the underlying assets to keep current tenants or attract new tenants. Estimated losses are recorded as a charge to earnings to establish an allowance for credit losses that we estimate to be adequate based on these factors. Based on the review of the above criteria, we did not record an allowance for credit losses for our notes receivable during the three months ended March 31, 2015 and 2014.
Application of New Accounting Standards	Application of New Accounting Standards
	In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update 2014-09, Revenue from Contracts with Customers (“ASU 2014-09”), which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. ASU 2014-09 will replace most existing revenue recognition guidance when it becomes effective on January 1, 2017. Early adoption is not permitted. ASU 2014-09 permits the use of either the retrospective or cumulative effect transition method. We have not yet selected a transition method and are evaluating the impact that ASU 2014-09 will have on our consolidated financial statements or related disclosures.
	In August 2014, the FASB issued Accounting Standards Update 2014-15, Disclosure of Uncertainties about an Entity's Ability to Continue as a Going Concern (“ASU 2014-15”), which requires an entity to evaluate whether conditions or events, in the aggregate, raise substantial doubt about the entity's ability to continue as a going concern for one year from the date the financial statements are issued or are available to be issued. The guidance will become effective January 1, 2017. The adoption of ASU 2014-15 is not expected to have an impact on our consolidated financial statements or related disclosures.
	In January 2015, the FASB issued Accounting Standards Update 2015-01, Simplifying Income Statement Presentation by Eliminating the Concept of Extraordinary Items ("ASU 2015-01"), which eliminates the concept of extraordinary items from GAAP and the requirement that an entity separately report extraordinary items in the income statement. ASU 2015-01 also requires that entities continue to evaluate whether items are unusual in nature or infrequent in occurrence for presentation and disclosure purposes. ASU 2015-01 applies to all entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2015. Early adoption is permitted and the guidance may be applied prospectively or retrospectively to all prior periods presented in the consolidated financial statements. The adoption of ASU 2015-01 is not expected to have a material impact on our consolidated financial statements or related disclosures.
Reclassifications	Reclassifications
	Certain prior year amounts have been reclassified to conform to the current year presentation as a result of reclassifying the operating results of several properties as discontinued operations. For more information, see note 7, Dispositions.

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Estimated Useful Life of Assets	The estimated useful lives of our assets, by class, are as follows:
	Buildings	39 years
	Building improvements	5 to 20 years
	Furniture, fixtures and equipment	5 to 15 years
	Lease related intangible assets	The term of the related lease
	Tenant improvements	Shorter of the useful life of the asset or the term of the related lease

Earnings_Per_Common_Share_Tabl

Earnings Per Common Share (Tables)	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Computation of Company's Basic and Diluted Earnings Per Share	The following table sets forth the computation of our basic and diluted earnings per common share (amounts in thousands, except per share amounts):
		Three Months Ended March 31,
		2015				2014
	Numerator for basic and diluted earnings per common share:
	Income (loss) from continuing operations	$	1,099			$	(586	)
	Loss from discontinued operations	(607		)		(857		)
	Net income (loss)	492				(1,443		)
	Less: Net loss from continuing operations attributable to noncontrolling interests	86				155
	Less: Net loss from discontinued operations attributable to noncontrolling interests	26				40
	Net income (loss) attributable to First Potomac Realty Trust	604				(1,248		)
	Less: Dividends on preferred shares	(3,100		)		(3,100		)
	Net loss attributable to common shareholders	(2,496		)		(4,348		)
	Less: Allocation to participating securities	(73		)		(78		)
	Net loss attributable to common shareholders	$	(2,569	)		$	(4,426	)
	Denominator for basic and diluted earnings per common share:
	Weighted average common shares outstanding - basic and diluted	58,225				58,097
	Basic and diluted earnings per common share:
	Loss from continuing operations	$	(0.03	)		$	(0.07	)
	Loss from discontinued operations	(0.01		)		(0.01		)
	Net loss	$	(0.04	)		$	(0.08	)
Anti-Dilutive Shares Not Included in Calculation of Diluted Earnings Per Share	In accordance with GAAP regarding earnings per common share, we did not include the following potential weighted average common shares in our calculation of diluted earnings per common share as they are anti-dilutive for the periods presented (amounts in thousands):
		Three Months Ended
		March 31,
		2015			2014
	Stock option awards	1,083			1,206
	Non-vested share awards	380			414
	Series A Preferred Shares(1)	13,032			12,671
		14,495			14,291
	(1)	Our Series A Preferred Shares are only convertible into our common shares upon certain changes in control of our Company. The dilutive shares are calculated as the daily average of the face value of the Series A Preferred Shares divided by the outstanding common share price.

Rental_Property_Tables

Rental Property (Tables)	3 Months Ended
	Mar. 31, 2015
Real Estate [Abstract]
Summary of Rental Property	Rental property consists of the following (dollars in thousands):
		March 31, 2015			December 31, 2014(1)
	Land and land improvements	$	325,228		$	325,214
	Buildings and improvements	950,746			949,683
	Construction in progress	73,444			69,181
	Tenant improvements	170,443			159,867
	Furniture, fixtures and equipment	402			427
		1,520,263			1,504,372
	Less: accumulated depreciation	(227,368		)	(215,499		)
		$	1,292,895		$	1,288,873
	(1) Excludes rental property totaling $57.7 million at December 31, 2014 related to the sale of the Richmond Portfolio (as defined in note 7, Dispositions), which was classified as held-for-sale at December 31, 2014 and was sold on March 19, 2015.

Notes_Receivable_Tables

Notes Receivable (Tables)	3 Months Ended
	Mar. 31, 2015
Receivables [Abstract]
Summary of Notes Receivable	Below is a summary of our notes receivable for our outstanding mezzanine loans (dollars in thousands):
		Balance at March 31, 2015
	Property	Face Amount		Unamortized			Balance		Interest Rate
				Origination Fees
	950 F Street, NW	$	34,000	$	—		$	34,000	9.75	%
		Balance at December 31, 2014
	Property	Face Amount		Unamortized			Balance		Interest Rate
				Origination Fees
	950 F Street, NW	$	34,000	$	—		$	34,000	9.75	%
	America’s Square	29,720		(41		)	29,679		9	%
		$	63,720	$	(41	)	$	63,679

Investment_in_Affiliates_Table

Investment in Affiliates (Tables)	3 Months Ended
	Mar. 31, 2015
Equity Method Investments and Joint Ventures [Abstract]
Components of Investments in Affiliates	Our investment in affiliates consisted of the following (dollars in thousands):
		Reporting Segment		Ownership			31-Mar-15		31-Dec-14
				Interest
	Prosperity Metro Plaza	Northern Virginia		51	%		$	24,846	$	24,651
	1750 H Street, NW	Washington, D.C.		50	%		14,938		14,834
	Aviation Business Park	Maryland		50	%		5,677		5,748
	RiversPark I and II(1)	Maryland		25	%		2,197		2,249
							$	47,658	$	47,482
	(1) RiversPark I and RiversPark II are owned through two separate joint ventures.
Net Assets of Company's Unconsolidated Joint Ventures	The net assets of our unconsolidated joint ventures consisted of the following (dollars in thousands):
		March 31, 2015				December 31, 2014
	Assets:
	Rental property, net	$	193,201			$	193,533
	Cash and cash equivalents	5,143				4,567
	Other assets	16,514				16,748
	Total assets	214,858				214,848
	Liabilities:
	Mortgage loans(1)	110,000				110,000
	Other liabilities	6,729				7,256
	Total liabilities	116,729				117,256
	Net assets	$	98,129			$	97,592
	(1)	Of the total mortgage debt that encumbers our unconsolidated properties, $2.8 million is recourse to us. We believe the fair value of the potential liability to us under this guaranty is inconsequential as the likelihood of our need to perform under the debt agreement is remote.
Results of Operations of Company's Unconsolidated Joint Ventures	The following table summarizes the results of operations of our unconsolidated joint ventures, which due to our varying ownership interests in the joint ventures and the varying operations of the joint ventures may or may not be reflective of the amounts recorded in our consolidated statements of operations (dollars in thousands):
		Three Months Ended
		March 31,
		2015				2014
	Total revenues	$	6,167			$	5,752
	Total operating expenses	(2,156		)		(2,226		)
	Net operating income	4,011				3,526
	Depreciation and amortization	(2,249		)		(2,803		)
	Interest expense, net	(973		)		(1,011		)
	Net income (loss)	$	789			$	(288	)

Dispositions_Tables

Dispositions (Tables)	3 Months Ended
	Mar. 31, 2015
Discontinued Operations and Disposal Groups [Abstract]
Discontinued Operations Square Feet Area [Table Text Block]	The following table is a summary of completed property dispositions whose operating results are included in continuing operations in our consolidated statements of operations for the periods presented (dollars in thousands):
		Reporting	Disposition Date	Property Type	Square Feet		Net Sale Proceeds
		Segment
	Owings Mills Business Park	Maryland	10/16/14	Business Park	180,475		$	12,417
	Corporate Campus at Ashburn Center	Northern Virginia	6/26/14	Business Park	194,184		39,910
Schedule of Disposal Groups Including Not Discontinued Operations, Income Statement, Balance Sheet and Additional Disclosures [Table Text Block]	The following table summarizes the aggregate results of operations for the two properties that are included in continuing operations for the three months ended March 31, 2014 (dollars in thousands):
				2014
	Revenues			$	1,465
	Property operating expenses			(548		)
	Depreciation and amortization			(366		)
	Net income from continuing operations			$	551
Summary of Completed Property Dispositions	The following table is a summary of completed property dispositions whose operating results are reflected as discontinued operations in our consolidated statements of operations for the periods presented (dollars in thousands):
		Reporting	Disposition Date	Property Type	Square Feet		Net Sale Proceeds
		Segment
	Richmond Portfolio	Southern Virginia	3/19/15	Business Park	827,900		$	53,768
	Patrick Center	Maryland	4/16/14	Office	66,269		10,888
	West Park	Maryland	4/2/14	Office	28,333		2,871
	Girard Business Center and Gateway Center	Maryland	1/29/14	Business Park and  Office	341,973		31,616
Schedule of Disposal Groups, Including Discontinued Operations, Income Statement, Balance Sheet and Additional Disclosures	The following table summarizes the results of operations of properties included in discontinued operations (dollars in thousands):
		Three Months Ended
		March 31,
		2015				2014
	Revenues	$	877			$	1,808
	Loss from operations, before taxes(1)	(975		)		(911		)
	Loss on debt extinguishment	(489		)		—
	Gain on sale of rental property	857				54
	(1)	For the three months ended March 31, 2015, we accelerated $2.0 million of unamortized straight-line rents, deferred rent abatements and leasing commissions related to the sale of the Richmond Portfolio in March 2015. For the three months ended March 31, 2014, we accelerated $1.5 million of unamortized straight-line rents, deferred rent abatements and leasing commissions related to the sale of both Girard Business Center and Gateway Center in January 2014.

Debt_Tables

Debt (Tables)	3 Months Ended
	Mar. 31, 2015
Debt Disclosure [Abstract]
Schedule of Borrowings	Our borrowings consisted of the following (dollars in thousands):
		March 31,				December 31, 2014(1)
		2015
	Mortgage loans, effective interest rates ranging from 4.40% to 6.01%, maturing at various dates through June 2023(2)	$	303,866			$	308,637
	Unsecured term loan, effective interest rates ranging from LIBOR plus 1.65% to LIBOR plus 2.05%, with staggered maturity dates ranging from October 2018 to October 2020(2)	300,000				300,000
	Unsecured revolving credit facility, effective interest rate of LIBOR plus 1.70%, maturing October 2017(2)	143,000				205,000
		$	746,866			$	813,637
	(1)	Includes five mortgage loans that were repaid with the sale of the Richmond Portfolio on March 19, 2015. At December 31, 2014, the mortgage loans had an aggregate principal balance of $3.5 million and were classified within “Liabilities held-for-sale” on our consolidated balance sheet for December 31, 2014.
	(2)	At March 31, 2015, LIBOR was 0.18%. All references to LIBOR in the condensed consolidated financial statements refer to one-month LIBOR.
Summary of Company's Mortgage Debt	The following table provides a summary of our mortgage debt at March 31, 2015 and December 31, 2014 (dollars in thousands):
	Encumbered Property		Contractual		Effective			Maturity	March 31,			31-Dec-14
			Interest Rate		Interest			Date	2015
					Rate
	Jackson National Life Loan(1)		5.19%		5.19	%		Aug-15	$	64,640		$	64,943
	440 First Street, NW(2)		LIBOR + 2.50%		LIBOR + 2.50%			May-16	32,216			32,216
	Storey Park(2)		LIBOR + 2.50%		LIBOR + 2.50%			Oct-16	22,000			22,000
	Gateway Centre Manassas Building I		7.35%		5.88	%		November 2016	378			432
	Hillside I and II		5.75%		4.62	%		Dec-16	12,846			12,949
	Redland Corporate Center Buildings II & III		4.20%		4.64	%		Nov-17	65,503			65,816
	840 First Street, NE		5.72%		6.01	%		Jul-20	36,379			36,539
	Battlefield Corporate Center		4.26%		4.4	%		Nov-20	3,651			3,692
	1211 Connecticut Avenue, NW		4.22%		4.47	%		Jul-22	29,548			29,691
	1401 K Street, NW		4.80%		4.93	%		Jun-23	36,705			36,861
					4.75	%	(3)		303,866			305,139
	Unamortized fair value adjustments								(320		)	(370		)
	Principal balance								303,546			304,769
	Richmond Portfolio(4)
	Hanover Business Center Building D		8.88%		6.63	%		Aug-15	—			104
	Chesterfield Business Center Buildings C,D,G and H		8.50%		6.63	%		Sep-15	—			302
	Hanover Business Center Building C		7.88%		6.63	%		Dec-17	—			505
	Chesterfield Business Center Buildings A,B,E and F		7.45%		6.63	%		Jun-21	—			1,674
	Airpark Business Center		7.45%		6.63	%		Jun-21	—			913
									—			3,498
	Total unamortized fair value adjustments - Richmond								—			(73		)
	Total principal balance - Richmond								$	—		$	3,425
	Total principal balance								$	303,546		$	308,194
	(1)	At March 31, 2015, the loan was secured by the following properties: Plaza 500, Van Buren Office Park, Rumsey Center, Snowden Center, Greenbrier Technology Center II and Norfolk Business Center. The terms of the loan allow us to substitute collateral, as long as certain debt-service coverage and loan-to-value ratios are maintained, or to prepay a portion of the loan, with a prepayment penalty, subject to a debt-service yield.
	(2)	At March 31, 2015, LIBOR was 0.18%.
	(3)	Weighted average interest rate on total mortgage debt.
	(4)	The mortgage loans and unamortized fair value adjustments that encumbered properties within the Richmond Portfolio were classified within “Liabilities held-for-sale” on our consolidated balance sheet at December 31, 2014. The loans were prepaid upon the sale of the Richmond Portfolio on March 19, 2015.
Unsecured Term Loan	The table below shows the outstanding balances and the interest rates of the three tranches of the $300.0 million unsecured term loan at March 31, 2015 (dollars in thousands):
		Maturity Date		Amount				Interest Rate(1)
	Tranche A	October 2018		$	100,000			LIBOR, plus 165 basis points
	Tranche B	October 2019		100,000				LIBOR, plus 180 basis points
	Tranche C	October 2020		100,000				LIBOR, plus 205 basis points
				$	300,000
	(1)	At March 31, 2015, LIBOR was 0.18%. The interest rate spread is subject to change based on our maximum total indebtedness ratio. For more information, see note 8(e) Debt – Financial Covenants.

Derivative_Instruments_Tables

Derivative Instruments (Tables)	3 Months Ended
	Mar. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Summary of Interest Rate Swap Agreements	Our interest rate swap agreements are summarized below (dollars in thousands):
	Maturity Date	Notional		Interest Rate	Fixed LIBOR
		Amount		Contractual	Interest Rate
				Component
	Jul-16	$	35,000	LIBOR	1.754	%
	Jul-16	25,000		LIBOR	1.763	%
	Jul-17	30,000		LIBOR	2.093	%
	Jul-17	30,000		LIBOR	2.093	%
	Jul-17	25,000		LIBOR	1.129	%
	Jul-17	12,500		LIBOR	1.129	%
	Jul-17	50,000		LIBOR	0.955	%
	Jul-18	12,500		LIBOR	1.383	%
	Jul-18	30,000		LIBOR	1.66	%
	Jul-18	25,000		LIBOR	1.394	%
	Jul-18	25,000		LIBOR	1.135	%
	Total/Weighted Average	$	300,000		1.505	%

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value of Assets and Liabilities	In accordance with accounting provisions and the fair value hierarchy described above, the following table shows the fair value of our consolidated assets and liabilities that are measured on a non-recurring and recurring basis as of March 31, 2015 and December 31, 2014 (dollars in thousands):
		Balance at		Level 1		Level 2		Level 3
		March 31, 2015
	Recurring Measurements:
	Derivative instrument-swap liabilities	$	4,518	$	—	$	4,518	$	—
		Balance at		Level 1		Level 2		Level 3
		December 31, 2014
	Recurring Measurements:
	Derivative instrument-swap assets	$	133	$	—	$	133	$	—
	Derivative instrument-swap liabilities	3,569		—		3,569		—
Fair Value of Debt Instruments	The carrying amount and estimated fair value of our notes receivable and debt instruments are as follows (amounts in thousands):
		March 31, 2015				December 31, 2014
		Carrying		Fair		Carrying		Fair
		Value		Value		Value		Value
	Financial Assets:
	Notes receivable(1)	$	34,000	$	34,000	$	63,679	$	63,720
	Financial Liabilities:
	Mortgage debt(2)	$	303,866	$	299,042	$	308,637	$	292,882
	Unsecured term loan	300,000		300,000		300,000		300,000
	Unsecured revolving credit facility	143,000		143,000		205,000		205,000
	Total	$	746,866	$	742,042	$	813,637	$	797,882
	(1)	The principal amount of our notes receivable was $34.0 million and $63.7 million at March 31, 2015 and December 31, 2014, respectively.
		On February 24, 2015, the owners of America’s Square, a 461,000 square foot office complex located in Washington, D.C., prepaid a mezzanine loan, which had an outstanding $29.7 million balance of the $30.0 million mezzanine loan that we provided them in April 2011.
	(2)	Includes five mortgage loans that were repaid with the sale of the Richmond Portfolio on March 19, 2015. At December 31, 2014, the mortgage loans had an aggregate principal balance of $3.5 million and were classified within “Liabilities held-for-sale” on our consolidated balance sheet for December 31, 2014.

Equity_Tables

Equity (Tables)	3 Months Ended
	Mar. 31, 2015
Equity [Abstract]
Company's Allocation between Non-controlling Interests	Our equity and redeemable noncontrolling interests are as follows (dollars in thousands):
		First			Non-redeemable			Total Equity			Redeemable
		Potomac			noncontrolling						noncontrolling
		Realty Trust			interests						interests
	Balance at December 31, 2014	$	710,007		$	898		$	710,905		$	33,332
	Net income (loss)	604			—			604			(112		)
	Changes in ownership, net	1,281			(96		)	1,185			(581		)
	Distributions to owners	(11,902		)	—			(11,902		)	(395		)
	Other comprehensive loss	(1,030		)	—			(1,030		)	(46		)
	Balance at March 31, 2015	$	698,960		$	802		$	699,762		$	32,198
		First			Non-redeemable			Total Equity			Redeemable
		Potomac			noncontrolling						noncontrolling
		Realty Trust			interests						interests
	Balance at December 31, 2013	$	738,510		$	781		$	739,291		$	33,221
	Net loss	(1,248		)	—			(1,248		)	(195		)
	Changes in ownership, net	(1,502		)	89			(1,413		)	2,067
	Distributions to owners	(11,889		)	—			(11,889		)	(393		)
	Other comprehensive income	168			—			168			7
	Balance at March 31, 2014	$	724,039		$	870		$	724,909		$	34,707
Company's Accumulated Other Comprehensive Loss	A summary of our accumulated other comprehensive loss is as follows (dollars in thousands):
		2015			2014
	Beginning balance at January 1,	$	(3,268	)	$	(3,836	)
	Net unrealized (loss) gain on derivative instruments	(1,076		)	175
	Net loss (gain) attributable to noncontrolling interests	46			(7		)
	Ending balance at March 31,	$	(4,298	)	$	(3,668	)

ShareBased_Payments_Tables

Share-Based Payments (Tables)	3 Months Ended
	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Compensation Plans Option Activity	A summary of our stock option activity during the three months ended March 31 is presented below:
		Options		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term	Aggregate Intrinsic Value
	Outstanding at December 31, 2014	1,051,359		$	15.33	6.3 years	$	181,352
	Granted	119,500		12.48
	Exercised	(2,000	)	9.3
	Expired	(59,000	)	22.44
	Forfeited	(49,771	)	14.48
	Outstanding at March 31, 2015	1,060,088		$	14.67	6.8 years	$	107,523
	Exercisable at March 31, 2015	516,839		$	15.52	5.8 years	$	87,260
	Options expected to vest, subsequent to March 31, 2015	507,651		$	13.97	7.6 years	$	17,602
Assumptions Used in Fair Value Determination of Stock Options Granted	The weighted average assumptions used in the fair value determination of stock options granted to employees during the three months ended March 31, 2015 are summarized as follows:
	Risk-free interest rate	1.61	%
	Expected volatility	29.16	%
	Expected dividend yield	4.79	%
	Weighted average expected life of options	5 years
Schedule of Nonvested Share Activity	A summary of our non-vested common share awards at March 31, 2015 is as follows:
		Non-vested		Weighted
		Common		Average Grant
		Shares		Date Fair Value
	Non-vested at December 31, 2014	623,421		$	13.16
	Granted	121,380		12.11
	Vested	(106,300	)	13.97
	Expired	(22,260	)	8.42
	Forfeited	(154,626	)	13.42
	Non-vested at March 31, 2015	461,615		$	12.83

Segment_Information_Tables

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2015
Segment Reporting [Abstract]
Summary of Segment Information	The results of operations of our four reporting segments for the three months ended March 31, 2015 and 2014 are as follows (dollars in thousands):
		Three Months Ended March 31, 2015
		Washington, D.C.			Maryland			Northern Virginia			Southern Virginia			Consolidated
	Number of buildings(1)	6			38			49			19			112
	Square feet(1)	916,686			1,999,300			3,021,299			2,024,003			7,961,288
	Total revenues	$	11,032		$	11,705		$	14,114		$	6,998		$	43,849
	Property operating expense	(3,139		)	(4,018		)	(4,064		)	(1,892		)	(13,113		)
	Real estate taxes and insurance	(2,023		)	(891		)	(1,549		)	(579		)	(5,042		)
	Total property operating income	$	5,870		$	6,796		$	8,501		$	4,527		25,694
	Depreciation and amortization expense													(16,335		)
	General and administrative													(5,526		)
	Other expenses													(2,734		)
	Loss from discontinued operations													(607		)
	Net income													$	492
	Total assets(2)(3)	$	503,651		$	358,772		$	444,596		$	167,979		$	1,534,448
	Capital expenditures(4)	$	3,436		$	2,164		$	10,843		$	2,490		$	19,242
		Three Months Ended March 31, 2014
		Washington, D.C.			Maryland			Northern Virginia			Southern Virginia			Consolidated
	Number of buildings(1)(5)	4			44			51			38			137
	Square feet(1)(5)	522,560			2,274,813			3,086,550			2,851,465			8,735,388
	Total revenues	$	6,940		$	11,645		$	13,666		$	7,112		$	39,363
	Property operating expense	(1,987		)	(3,946		)	(3,976		)	(2,129		)	(12,038		)
	Real estate taxes and insurance	(1,054		)	(1,004		)	(1,524		)	(550		)	(4,132		)
	Total property operating income	$	3,899		$	6,695		$	8,166		$	4,433		23,193
	Depreciation and amortization expense													(14,310		)
	General and administrative													(5,196		)
	Acquisition costs													(68		)
	Other expenses													(4,205		)
	Loss from discontinued operations													(857		)
	Net loss													$	(1,443	)
	Total assets(2)(3)	$	343,804		$	393,919		$	421,556		$	230,384		$	1,481,336
	Capital expenditures(4)	$	6,481		$	2,390		$	822		$	1,423		$	11,393
	(1)	Excludes Storey Park from our Washington, D.C. reporting segment, which was placed in development in the third quarter of 2013.
	(2)	Total assets include our investment in properties that are owned through joint ventures that are not consolidated within our condensed consolidated financial statements. For more information on our unconsolidated investments, including location within our reportable segments, see note 6, Investment in Affiliates.
	(3)	Corporate assets not allocated to any of our reportable segments totaled $59,450 and $91,673 at March 31, 2015 and 2014, respectively.
	(4)	Capital expenditures for corporate assets not allocated to any of our reportable segments totaled $309 and $277 for the three months ended March 31, 2015 and 2014, respectively.
	(5)	Includes occupied space at 440 First Street, NW in our Washington, D.C. reporting segment, which was substantially completed in the third quarter of 2013. In October 2014, the property was placed in service.

Description_of_Business_Additi

Description of Business - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
	Person	sqft
	JointVenture
	segment
	sqft
	Executives
Real Estate Properties [Line Items]
Number of Reportable Segments	4
Operating Partnership in preferred	100.00%
Interest in Operating Partnership	95.70%
Number of officers who owned limited partnership interests	2
Area of real estate property	7,961,288	8,735,388
Unconsolidated joint ventures	5
Square footage of land for additional development	1,300,000
Occupancy rate in the Company's consolidated properties	88.00%
Number of tenants representing current occupancy rate	500
Square footage in development or redevelopment not included on occupancy calculation	200,000
Percent of Annualized Cash Rent	25.90%
Wholly-owned Properties [Member]
Real Estate Properties [Line Items]
Number of Reportable Segments	4
Area of real estate property	8,000,000
Unconsolidated Properties [Member]
Real Estate Properties [Line Items]
Area of real estate property	900,000
US Government [Member]
Real Estate Properties [Line Items]
Percent of Annualized Cash Rent	13.20%

Summary_of_Significant_Account3

Summary of Significant Accounting Policies - Estimated Useful Lives of Company's Assets, by Class (Detail)	3 Months Ended
	Mar. 31, 2015
Property, Plant and Equipment [Line Items]
Lease related intangible assets	The term of the related lease
Tenant improvements	Shorter of the useful life of the asset or the term of the related lease
Buildings
Property, Plant and Equipment [Line Items]
Useful life	39 years
Minimum [Member] | Building improvements
Property, Plant and Equipment [Line Items]
Useful life	5 years
Minimum [Member] | Furniture, fixtures and equipment
Property, Plant and Equipment [Line Items]
Useful life	5 years
Maximum | Building improvements
Property, Plant and Equipment [Line Items]
Useful life	20 years
Maximum | Furniture, fixtures and equipment
Property, Plant and Equipment [Line Items]
Useful life	15 years

Summary_of_Significant_Account4

Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Accounting Policies [Abstract]
Allowance for credit losses for its notes receivable	$0	$0

Earnings_Per_Common_Share_Comp

Earnings Per Common Share - Computation of Company's Basic and Diluted Earnings Per Share (Detail) (USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Numerator for basic and diluted earnings per common share:
Income (loss) from continuing operations	$1,099	($586)
Loss from discontinued operations	-607	-857
Net income (loss)	492	-1,443
Less: Net loss from continuing operations attributable to noncontrolling interests	86	155
Less: Net loss from discontinued operations attributable to noncontrolling interests	26	40
Net income (loss) attributable to First Potomac Realty Trust	604	-1,248
Less: Dividends on preferred shares	-3,100	-3,100
Net loss attributable to common shareholders	-2,496	-4,348
Less: Allocation to participating securities	73	78
Net loss attributable to common shareholders	($2,569)	($4,426)
Denominator for basic and diluted earnings per common share:
Diluted	58,225	58,097
Basic and diluted earnings per common share:
Loss from continuing operations	($0.03)	($0.07)
Loss from discontinued operations	($0.01)	($0.01)
Net loss	($0.04)	($0.08)

Earnings_Per_Common_Share_Anti

Earnings Per Common Share - Anti-Dilutive Shares Not Included in Calculation of Diluted Earnings Per Share (Detail)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, Amount	14,495	14,291
Stock option awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, Amount	1,083	1,206
Non-vested share awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, Amount	380	414
Series A Preferred Shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, Amount	13,032	12,671

Rental_Property_Summary_of_Ren

Rental Property - Summary of Rental Property (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Property, Plant and Equipment [Line Items]
Rental property, net	$1,292,895	$1,288,873
Rental Property [Member]
Property, Plant and Equipment [Line Items]
Land and land improvements	325,228	325,214
Buildings and improvements	950,746	949,683
Construction in process	73,444	69,181
Tenant improvements	170,443	159,867
Furniture, fixtures and equipment	402	427
Rental property, gross	1,520,263	1,504,372
Less: accumulated depreciation	-227,368	-215,499
Southern Virginia | Rental Property [Member]
Property, Plant and Equipment [Line Items]
Rental property, net		$57,700

Rental_Property_Additional_Inf

Rental Property - Additional Information (Detail) (USD $)	3 Months Ended	0 Months Ended
	Mar. 31, 2015	Aug. 04, 2011	Dec. 31, 2014
	sqft	acre
Segment Reporting Information [Line Items]
Area of land available for development in additional building space	1,300,000
Occupancy rate in the Company's consolidated properties	88.00%
440 First Street, NW [Member]
Segment Reporting Information [Line Items]
Original cost basis of the property	23,600,000
Projected incremental investment in redevelopment project	55,500,000
Anticipated completion of redevelopment	139,000
Occupancy rate in the Company's consolidated properties	58.90%		46.90%
Redevelopment Efforts Yet To Be Placed In Service	0
Washington D C Reporting Segment
Segment Reporting Information [Line Items]
Area of land available for development in additional building space	700,000
Lease expiration date		31-Aug-13
Development of area for operations by joint venture		1.6
Projected incremental investment in development project	56,000,000
Original cost basis of the property	43,300,000
Washington D C Reporting Segment | Maximum | Greyhound Property [Member]
Segment Reporting Information [Line Items]
Area of land available for development in additional building space		712,000
Washington D C Reporting Segment | 440 First Street, NW [Member]
Segment Reporting Information [Line Items]
Placed in-service redevelopment efforts	0
Maryland Reporting Segment [Member]
Segment Reporting Information [Line Items]
Area of land available for development in additional building space	100,000
Northern Virginia
Segment Reporting Information [Line Items]
Area of land available for development in additional building space	400,000
Area of land placed under development	167,000
Projected incremental investment in development project	10,200,000
Original cost basis of the property	5,200,000
Southern Virginia [Member]
Segment Reporting Information [Line Items]
Area of land available for development in additional building space	100,000

Notes_Receivable_Summary_of_No

Notes Receivable - Summary of Notes Receivable (Detail) (USD $)	3 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2013	Dec. 31, 2014
Receivables with Imputed Interest [Line Items]
Face Amount			$63,720
Unamortized Origination Fees			-41
Balance			63,679
Notes Receivables Issued on December 2010 [Member]
Receivables with Imputed Interest [Line Items]
Face Amount	34,000		34,000
Unamortized Origination Fees	0		0
Balance	34,000		34,000
Interest Rate	9.75%	9.75%
America Square [Member]
Receivables with Imputed Interest [Line Items]
Face Amount			29,720
Unamortized Origination Fees			-41
Balance			$29,679
Interest Rate		9.00%

Notes_Receivable_Additional_In

Notes Receivable - Additional Information (Detail) (USD $)	3 Months Ended		12 Months Ended	0 Months Ended	12 Months Ended	0 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2013	Apr. 01, 2011	Dec. 31, 2010	Jan. 10, 2014	Dec. 31, 2014	Feb. 24, 2015	Apr. 30, 2011
	sqft	sqft			sqft				sqft
Receivables with Imputed Interest [Line Items]
Area of real estate property	7,961,288	8,735,388
Unsecured revolving credit facility	$143,000,000						$205,000,000
Interest income	1,200,000
Income from amortization of origination fees	5,000	11,000
America Square [Member]
Receivables with Imputed Interest [Line Items]
Area of real estate property									461,000
Mezzanine loan provided to owners								29,700,000	30,000,000
Maturity date of loan	1-May-16
Prepayment Fee Income	2,400,000
Fixed interest rate on loan			9.00%
America Square [Member] | Maximum
Receivables with Imputed Interest [Line Items]
Fixed interest rate on loan				9.00%
Notes Receivables Issued on December 2010 [Member]
Receivables with Imputed Interest [Line Items]
Area of real estate property					287,000
Mezzanine loan provided to owners					25,000,000	34,000,000
Maturity date of loan					1-Apr-17
Unsecured revolving credit facility						9,000,000
Fixed interest rate on loan	9.75%		9.75%
Interest income		1,500,000
Write-off of unamortized origination fees		$100,000
Notes Receivables Issued on December 2010 [Member] | Maximum
Receivables with Imputed Interest [Line Items]
Fixed interest rate on loan						12.50%
Notes Receivables Issued on December 2010 [Member] | Minimum [Member]
Receivables with Imputed Interest [Line Items]
Fixed interest rate on loan						9.75%

Investment_in_Affiliates_Compo

Investment in Affiliates - Components of Investments in Affiliates (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Company Investment	$47,658		$47,482
Prosperity Metro Plaza
Schedule of Equity Method Investments [Line Items]
Reporting Segment	NorthernB Virginia
Ownership Interest	51.00%
Company Investment	24,846		24,651
1750 H Street, NW
Schedule of Equity Method Investments [Line Items]
Reporting Segment	Washington,B D.C.
Ownership Interest	50.00%
Company Investment	14,938		14,834
Aviation Business Park
Schedule of Equity Method Investments [Line Items]
Reporting Segment	Maryland
Ownership Interest	50.00%
Company Investment	5,677		5,748
RiversPark I and II
Schedule of Equity Method Investments [Line Items]
Reporting Segment	Maryland
Ownership Interest	25.00%	[1]
Company Investment	$2,197	[1]	$2,249	[1]
[1]	RiversPark I and RiversPark II are owned through two separate joint ventures.

Investment_in_Affiliates_Net_A

Investment in Affiliates - Net Assets of Company's Unconsolidated Joint Ventures (Detail) (USD $)	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Assets:
Rental property, net	$1,292,895		$1,288,873
Cash and cash equivalents	14,686		13,323		14,842	8,740
Total assets	1,534,448		1,618,460		1,481,336
Liabilities:
Total liabilities	802,488		874,223
Recourse mortgage debt	746,866		813,637
Unconsolidated Joint Ventures
Assets:
Rental property, net	193,201		193,533
Cash and cash equivalents	5,143		4,567
Other assets	16,514		16,748
Total assets	214,858		214,848
Liabilities:
Mortgage loans	110,000	[1]	110,000	[1]
Other liabilities	6,729		7,256
Total liabilities	116,729		117,256
Net assets	98,129		97,592
Unconsolidated Entities
Liabilities:
Recourse mortgage debt	$2,800
[1]	Of the total mortgage debt that encumbers our unconsolidated properties, $2.8 million is recourse to us. We believe the fair value of the potential liability to us under this guaranty is inconsequential as the likelihood of our need to perform under the debt agreement is remote.

Investment_in_Affiliates_Addit

Investment in Affiliates - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended		0 Months Ended
In Millions, unless otherwise specified	Sep. 26, 2014	Mar. 31, 2015	Mar. 31, 2014	Sep. 26, 2017	Nov. 12, 2014	Jul. 10, 2014
	Rate	sqft
Schedule of Equity Method Investments [Line Items]
Ownership percentage in unconsolidated joint venture		51.00%
Repaid mortgage					$48.30
Investment in affiliates variable interest entity square feet		327,000
Financing					50
Mortgage interest rate		3.91%
Loan Interest only payment date		31-Dec-24
Loan maturity date		1-Dec-29
Loan prepayment date		1-Jun-29
Interest rate increase (decrease)	-60.00%
Fees from joint ventures		0.1	0.1
1750 H Street
Schedule of Equity Method Investments [Line Items]
Ownership percentage in unconsolidated joint venture						50.00%
Repaid mortgage						27.9
Financing						32
Mortgage interest rate		3.92%
Loan maturity date		1-Aug-24
Loan prepayment date		1-Aug-21
RiversPark I and II
Schedule of Equity Method Investments [Line Items]
Ownership percentage in unconsolidated joint venture	25.00%
Investment in affiliates variable interest entity square feet		308,000
Financing	28
Percentage of outstanding principal	25.00%	10.00%
Washington D C Reporting Segment | Maximum | 1750 H Street
Schedule of Equity Method Investments [Line Items]
Investment in affiliates variable interest entity square feet		113,000
Subsequent Event | RiversPark I and II
Schedule of Equity Method Investments [Line Items]
Loan maturity date				26-Sep-17

Investment_in_Affiliates_Resul

Investment in Affiliates - Results of Operations of Company's Unconsolidated Joint Ventures (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Schedule of Equity Method Investments [Line Items]
Total revenues	$43,849	$39,363
Total operating expenses	-40,016	-35,744
Operating income	3,833	3,619
Depreciation and amortization	-16,335	-14,310
Interest expense, net	-2,734	-4,205
Net income (loss)	346	-227
Unconsolidated Joint Ventures
Schedule of Equity Method Investments [Line Items]
Total revenues	6,167	5,752
Total operating expenses	-2,156	-2,226
Operating income	4,011	3,526
Depreciation and amortization	-2,249	-2,803
Interest expense, net	-973	-1,011
Net income (loss)	$789	($288)

Dispositions_Additional_Inform

Dispositions - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
	sqft	Integer
	Integer	sqft
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Number Of Buildings	112	137
Square feet	7,961,288	8,735,388
Unsecured revolving credit facility	$143,000,000		$205,000,000
Rents received in advance	291,000	593,000
Richmond
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Disposition Date	19-Mar-15
Number Of Buildings	19
Square feet	827,900
Proceeds from sale of properties	53,768,000
Mortgage loans, effective interest rates ranging from 4.40% to 6.01%, maturing at various dates through June 2023(2)	3,700,000
Loan prepayment penalty	500,000
Unsecured revolving credit facility	48,000,000
Gain (loss) on sale of properties	900,000
Rents received in advance	900,000
Deferred leasing commissions	1,100,000
Unamortized straight-line rent	2,000,000
Disposed Richmond
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Square feet	828,000
Girard Business Center and Gateway Center [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Disposition Date	29-Jan-14
Square feet	341,973
Proceeds from sale of properties	31,616,000
Unamortized straight-line rent		$1,500,000

Dispositions_Dispositions_Disp

Dispositions Dispositions - Disposed or Held-for-Sale Properties within Continuing Operations (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2015	Oct. 16, 2014
			sqft
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square feet	8,735,388	7,961,288
Corporate Campus at Ashburn Center and Owings Mills Business Park | Continuing Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues	$1,465
Property operating expenses	-548
Depreciation and amortization	-366
Net income from continuing operations	551
MARYLAND | Owings Mills Business Park
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Reporting Segment		Maryland
Disposition Date		16-Oct-14
Property Type		Business Park
Square feet			180,475
Proceeds from sale of properties		12,417
Northern Virginia | Corporate Campus at Ashburn Center
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Reporting Segment		Northern Virginia
Disposition Date		26-Jun-14
Property Type		Business Park
Square feet		194,184
Proceeds from sale of properties		$39,910

Dispositions_Summary_of_Comple

Dispositions - Summary of Completed Property Dispositions (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
	sqft	sqft
Schedule Of Discontinued Operations [Line Items]
Square feet	7,961,288	8,735,388
Richmond
Schedule Of Discontinued Operations [Line Items]
Reporting Segment	Southern Virginia
Disposition Date	19-Mar-15
Property Type	Business Park
Square feet	827,900
Proceeds from sale of properties	$53,768
Patrick Center
Schedule Of Discontinued Operations [Line Items]
Reporting Segment	Maryland
Disposition Date	16-Apr-14
Property Type	Office
Square feet	66,269
Proceeds from sale of properties	10,888
Girard Business Center and Gateway Center
Schedule Of Discontinued Operations [Line Items]
Reporting Segment	Maryland
Disposition Date	29-Jan-14
Property Type	BusinessB ParkB andB Office
Square feet	341,973
Proceeds from sale of properties	31,616
West Park
Schedule Of Discontinued Operations [Line Items]
Reporting Segment	Maryland
Disposition Date	2-Apr-14
Property Type	Office
Square feet	28,333
Proceeds from sale of properties	$2,871

Dispositions_Net_Loss_Income_f

Dispositions - Net (Loss) Income from Discontinued Operations (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on debt extinguishment	($489)		$0
Discontinued Operations [Member] | All properties classified within discontinued operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues	877		1,808
Loss from operations, before taxes(1)	-975	[1]	-911	[1]
Gain on sale of rental property	$857		$54
[1]	For the three months ended March 31, 2015, we accelerated $2.0 million of unamortized straight-line rents, deferred rent abatements and leasing commissions related to the sale of the Richmond Portfolio in March 2015. For the three months ended March 31, 2014, we accelerated $1.5 million of unamortized straight-line rents, deferred rent abatements and leasing commissions related to the sale of both Girard Business Center and Gateway Center in January 2014.

Debt_Schedule_of_Borrowings_De

Debt - Schedule of Borrowings (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015		Dec. 31, 2014
Debt Instrument [Line Items]
Mortgage loans, effective interest rates ranging from 4.40% to 6.01%, maturing at various dates through June 2023(2)	$303,866,000	[1]	$308,637,000	[1],[2]
Unsecured revolving credit facility, effective interest rate of LIBOR plus 1.70%, maturing October 2017(2)	143,000,000	[2]	205,000,000	[1],[2]
Total long term debt	746,866,000		813,637,000
Effective interest rate on the notes	0.18%
Mortgage Loan [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, effective percentage rate range, minimum	4.40%
Debt instrument, interest rate, effective percentage rate range, maximum	6.01%
Debt instrument maturity date	Jun-23
Unsecured Term Loan, Effective Interest Rates Ranging from LIBOR Plus 1.45% to LIBOR Plus 1.90%, with Staggered Maturity Dates ranging from October 2018 to October 2020
Debt Instrument [Line Items]
Unsecured term loan, effective interest rates ranging from LIBOR plus 1.65% to LIBOR plus 2.05%, with staggered maturity dates ranging from October 2018 to October 2020(2)	300,000,000	[2]	300,000,000	[1],[2]
Debt instrument maturity date	October 2018 to October 2020
Debt Instrument Basis Spread On Variable Rate Minimum	1.65%
Debt Instrument Basis Spread On Variable Rate Maximum	2.05%
Unsecured revolving credit facility
Debt Instrument [Line Items]
Unsecured revolving credit facility, effective interest rate of LIBOR plus 1.70%, maturing October 2017(2)	13,000,000
Debt instrument maturity date	Oct-17
Effective interest rate on the notes	1.70%
Richmond
Debt Instrument [Line Items]
Mortgage loans, effective interest rates ranging from 4.40% to 6.01%, maturing at various dates through June 2023(2)	0		3,498,000
Mortgages Held-for-sale, Fair Value Disclosure	$3,500,000
[1]	At March 31, 2015, LIBOR was 0.18%. All references to LIBOR in the condensed consolidated financial statements refer to one-month LIBOR.
[2]	Includes five mortgage loans that were repaid with the sale of the Richmond Portfolio on March 19, 2015. At December 31, 2014, the mortgage loans had an aggregate principal balance of $3.5 million and were classified within bLiabilities held-for-saleb on our consolidated balance sheet for December 31, 2014

Debt_Summary_of_Companys_Mortg

Debt - Summary of Company's Mortgage Debt (Detail) (USD $)	0 Months Ended	3 Months Ended
In Thousands, unless otherwise specified	Jun. 05, 2013	Mar. 31, 2015		Dec. 31, 2014
Debt Instrument [Line Items]
Effective Interest Rate		0.18%
Total Mortgage Debt		$303,866	[1]	$308,637	[1],[2]
Debt, Weighted Average Interest Rate		4.75%	[3]
Carrying amount of mortgages		303,546		308,194
Effective Interest Rate		0.18%
LIBOR plus interest rate	2.50%
Jackson National Life Loan
Debt Instrument [Line Items]
Contractual Interest Rate		5.19%
Effective Interest Rate		5.19%	[4]
Maturity Date		Aug-15	[4]
Total Mortgage Debt		64,640	[4]	64,943	[4]
Effective Interest Rate		5.19%	[4]
440 First Street, NW Construction Loan
Debt Instrument [Line Items]
Contractual Interest Rate		2.50%
Contractual Interest Rate		LIBORB +B 2.50%
Maturity Date		May-16	[5]
Total Mortgage Debt		32,216	[5]	32,216	[5]
Storey Park
Debt Instrument [Line Items]
Contractual Interest Rate		2.50%
Contractual Interest Rate		LIBORB +B 2.50%
Maturity Date		Oct-16	[5]
Total Mortgage Debt		22,000	[5]	22,000	[5]
Gateway Centre Manassas Building I
Debt Instrument [Line Items]
Contractual Interest Rate		7.35%
Effective Interest Rate		5.88%
Maturity Date		NovemberB 2016
Total Mortgage Debt		378		432
Effective Interest Rate		5.88%
Hillside I and II
Debt Instrument [Line Items]
Contractual Interest Rate		5.75%
Effective Interest Rate		4.62%
Maturity Date		Dec-16
Total Mortgage Debt		12,846		12,949
Effective Interest Rate		4.62%
Redland Corporate Center Buildings II & III
Debt Instrument [Line Items]
Contractual Interest Rate		4.20%
Effective Interest Rate		4.64%
Maturity Date		Nov-17
Total Mortgage Debt		65,503		65,816
Effective Interest Rate		4.64%
840 First Street, NE
Debt Instrument [Line Items]
Contractual Interest Rate		5.72%
Effective Interest Rate		6.01%
Maturity Date		Jul-20
Total Mortgage Debt		36,379		36,539
Effective Interest Rate		6.01%
Battlefield Corporate Center
Debt Instrument [Line Items]
Contractual Interest Rate		4.26%
Effective Interest Rate		4.40%
Maturity Date		Nov-20
Total Mortgage Debt		3,651		3,692
Effective Interest Rate		4.40%
One thousand two hundred eleven Connecticut Avenue NW. [Member]
Debt Instrument [Line Items]
Contractual Interest Rate		4.22%
Effective Interest Rate		4.47%
Maturity Date		Jul-22
Total Mortgage Debt		29,548		29,691
Effective Interest Rate		4.47%
1401 K Street, NW
Debt Instrument [Line Items]
Contractual Interest Rate		4.80%
Effective Interest Rate		4.93%
Maturity Date		1-Jun-23
Total Mortgage Debt		36,705		36,861
Effective Interest Rate		4.93%
Hanover Business Center Building D
Debt Instrument [Line Items]
Contractual Interest Rate		8.88%	[6]
Effective Interest Rate		6.63%	[6]
Maturity Date		Aug-15	[6]
Total Mortgage Debt		0	[6]	104	[6]
Effective Interest Rate		6.63%	[6]
Chesterfield Business Center Buildings C,D,G and H
Debt Instrument [Line Items]
Contractual Interest Rate		8.50%	[6]
Effective Interest Rate		6.63%	[6]
Maturity Date		Sep-15	[6]
Total Mortgage Debt		0	[6]	302	[6]
Effective Interest Rate		6.63%	[6]
Hanover Business Center Building C
Debt Instrument [Line Items]
Contractual Interest Rate		7.88%	[6]
Effective Interest Rate		6.63%	[6]
Maturity Date		Dec-17	[6]
Total Mortgage Debt		0	[6]	505	[6]
Effective Interest Rate		6.63%	[6]
Buildings Abe And F
Debt Instrument [Line Items]
Contractual Interest Rate		7.45%	[6]
Effective Interest Rate		6.63%	[6]
Maturity Date		Jun-21	[6]
Total Mortgage Debt		0	[6]	1,674	[6]
Effective Interest Rate		6.63%	[6]
Airpark Business Center
Debt Instrument [Line Items]
Contractual Interest Rate		7.45%	[6]
Effective Interest Rate		6.63%	[6]
Maturity Date		Jun-21	[6]
Total Mortgage Debt		0	[6]	913	[6]
Effective Interest Rate		6.63%	[6]
Continuing Operations
Debt Instrument [Line Items]
Total Mortgage Debt		303,866		305,139
Total unamortized fair value adjustments - Richmond		-320		-370
Carrying amount of mortgages		303,546		304,769
Richmond
Debt Instrument [Line Items]
Total Mortgage Debt		0		3,498
Total unamortized fair value adjustments - Richmond		0		-73
Richmond | Mortgage Loans
Debt Instrument [Line Items]
Carrying amount of mortgages		$0		$3,425
[1]	At March 31, 2015, LIBOR was 0.18%. All references to LIBOR in the condensed consolidated financial statements refer to one-month LIBOR.
[2]	Includes five mortgage loans that were repaid with the sale of the Richmond Portfolio on March 19, 2015. At December 31, 2014, the mortgage loans had an aggregate principal balance of $3.5 million and were classified within bLiabilities held-for-saleb on our consolidated balance sheet for December 31, 2014
[3]	Weighted average interest rate on total mortgage debt.
[4]	At March 31, 2015, the loan was secured by the following properties: Plaza 500, Van Buren Office Park, Rumsey Center, Snowden Center, Greenbrier Technology Center II and Norfolk Business Center. The terms of the loan allow us to substitute collateral, as long as certain debt-service coverage and loan-to-value ratios are maintained, or to prepay a portion of the loan, with a prepayment penalty, subject to a debt-service yield.
[5]	At March 31, 2015, LIBOR was 0.18%.
[6]	The mortgage loans and unamortized fair value adjustments that encumbered properties within the Richmond Portfolio were classified within bLiabilities held-for-saleb on our consolidated balance sheet at December 31, 2014. The loans were prepaid upon the sale of the Richmond Portfolio on March 19, 2015.

Debt_Additional_Information_De

Debt - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended			0 Months Ended	1 Months Ended
	Jun. 05, 2013	Mar. 31, 2015		Mar. 31, 2014	Oct. 16, 2014	Jan. 31, 2014	31-May-16	Dec. 31, 2014		Aug. 04, 2011
		Rate								Rate
		Interest_Rate_Swaps
		Integer
Debt Instrument [Line Items]
Amount borrowed				$21,700,000
Basis spread over variable rate	2.50%
Recourse mortgage debt		746,866,000						813,637,000
Outstanding balance of three tranches		300,000,000						300,000,000
Unsecured revolving credit facility, effective interest rate of LIBOR plus 1.70%, maturing October 2017(2)		143,000,000	[1]					205,000,000	[1],[2]
Interest rate during period		1.90%
Average interest rate at prior period end				1.70%
Maximum outstanding borrowings		218,000,000		112,000,000
Weighted average interest rate		1.90%
Available capacity on the unsecured revolving credit facility		138,200,000
Annual commitment fee		0.25%
Number of interest rate swap agreements		11
Fixed effective interest rate		1.50%
Line Of Credit Facility Basis Spread On Variable Rate Basis		1.70%
Unsecured term loan
Debt Instrument [Line Items]
Number of tranches		3
Outstanding balance of three tranches		300,000,000
Unsecured revolving credit facility
Debt Instrument [Line Items]
Unsecured revolving credit facility, effective interest rate of LIBOR plus 1.70%, maturing October 2017(2)		13,000,000
Proceed to pay loan		75,000,000
440 First Street, NW Construction Loan
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		2.50%
Interest Rate Swap
Debt Instrument [Line Items]
Fixed effective interest rate		1.51%
Amount on variable rate debt		300,000,000
Unused lines of credit
Debt Instrument [Line Items]
Weighted average borrowings outstanding on unsecured revolving credit facility		193,500,000		97,100,000
Greyhound Property [Member]
Debt Instrument [Line Items]
Percentage Of Interest In Joint Venture Owned By Entity										97.00%
Mortgage Loans on Real Estate					22,000,000
Debt Instrument, Interest Rate, Stated Percentage		5.00%
Basis spread over variable rate					2.50%
Maturity date					16-Oct-16
Maturity Period					1 year
Recourse mortgage debt					6,000,000
440 First Street, NW [Member]
Debt Instrument [Line Items]
Amount borrowed						10,500,000
Borrowing capacity of a construction loan	43,500,000
Maturity Period				1 year
Percentage of outstanding principal		50.00%
Subsequent Event [Member] | 440 First Street, NW [Member]
Debt Instrument [Line Items]
Maturity date							30-May-16
[1]	Includes five mortgage loans that were repaid with the sale of the Richmond Portfolio on March 19, 2015. At December 31, 2014, the mortgage loans had an aggregate principal balance of $3.5 million and were classified within bLiabilities held-for-saleb on our consolidated balance sheet for December 31, 2014
[2]	At March 31, 2015, LIBOR was 0.18%. All references to LIBOR in the condensed consolidated financial statements refer to one-month LIBOR.

Debt_Unsecured_Term_Loan_Detai

Debt - Unsecured Term Loan (Detail) (USD $)	0 Months Ended	3 Months Ended
In Thousands, unless otherwise specified	Jun. 05, 2013	Mar. 31, 2015		Dec. 31, 2014
Debt Instrument [Line Items]
Amount		$300,000		$300,000
Basis spread over variable rate	2.50%
Tranche A
Debt Instrument [Line Items]
Maturity Date		OctoberB 2018
Amount		100,000
Interest Rate		LIBOR,B plusB 165B basisB points	[1]
Basis spread over variable rate		1.65%
Tranche B
Debt Instrument [Line Items]
Maturity Date		OctoberB 2019
Amount		100,000
Interest Rate		LIBOR, plus 180 basis points	[1]
Basis spread over variable rate		1.80%
Tranche C
Debt Instrument [Line Items]
Maturity Date		OctoberB 2020
Amount		$100,000
Interest Rate		LIBOR, plus 205 basis points	[1]
Basis spread over variable rate		2.05%
[1]	At March 31, 2015, LIBOR was 0.18%. The interest rate spread is subject to change based on our maximum total indebtedness ratio. For more information, see note 8(e) Debt b Financial Covenants.

Derivative_Instruments_Summary

Derivative Instruments - Summary of Interest Rate Swap Agreements (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015
Derivatives, Fair Value [Line Items]
Fixed LIBOR Interest Rate	1.50%
Interest Rate Swap
Derivatives, Fair Value [Line Items]
Notional Amount	$300,000
Fixed LIBOR Interest Rate	1.51%
Interest Rate Swap One
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-16
Notional Amount	35,000
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	1.75%
Interest Rate Swap Two
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-16
Notional Amount	25,000
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	1.76%
Interest Rate Swap Three
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-17
Notional Amount	30,000
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	2.09%
Interest Rate Swap Four
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-17
Notional Amount	30,000
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	2.09%
Interest Rate Swap Five
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-18
Notional Amount	30,000
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	1.66%
Interest Rate Swap Six
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-18
Notional Amount	25,000
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	1.39%
Interest Rate Swap Seven
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-17
Notional Amount	25,000
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	1.13%
Interest Rate Swap Eight
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-17
Notional Amount	12,500
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	1.13%
Interest Rate Swap Nine
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-18
Notional Amount	12,500
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	1.38%
Interest Rate Swap Ten
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-17
Notional Amount	50,000
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	0.96%
Interest Rate Swap Eleven
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-18
Notional Amount	$25,000
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	1.14%

Derivative_Instruments_Additio

Derivative Instruments - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Derivatives, Fair Value [Line Items]
Number of interest rate swap agreements	11
Fixed effective interest rate	1.50%
Interest Rate Swap
Derivatives, Fair Value [Line Items]
Fixed effective interest rate	1.51%
Amount on variable rate debt	$300,000,000
Interest Rate Swap | Interest Expense
Derivatives, Fair Value [Line Items]
Accumulated other comprehensive loss reclassified as an increase in interest expense	1,000,000	1,000,000
Estimated accumulated other comprehensive loss reclassified as an increase in interest expense over the following twelve months	$4,300,000

Fair_Value_Measurements_Fair_V

Fair Value Measurements - Fair Value of Assets and Liabilities (Detail) (Recurring Measurements, USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Recurring Measurements:
Derivative instrument-swap assets		$133
Derivative instrument-swap liabilities	4,518	3,569
Level 1
Recurring Measurements:
Derivative instrument-swap assets		0
Derivative instrument-swap liabilities	0	0
Level 2
Recurring Measurements:
Derivative instrument-swap assets		133
Derivative instrument-swap liabilities	4,518	3,569
Level 3
Recurring Measurements:
Derivative instrument-swap assets		0
Derivative instrument-swap liabilities	$0	$0

Fair_Value_Measurements_Additi

Fair Value Measurements - Additional Information (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015
	snapshot
Derivatives, Fair Value [Line Items]
Number of Interest Rate Derivatives Held	11
Interest Rate Swap
Derivatives, Fair Value [Line Items]
Notional Amount	$300,000
Minimum number of daily snapshot used for valuation of interest rate swap agreements	7,500

Fair_Value_Measurements_Fair_V1

Fair Value Measurements - Fair Value of Debt Instruments (Detail) (USD $)	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014	Feb. 24, 2015	Apr. 30, 2011
	sqft				sqft		sqft
Financial Assets:
Carrying value of notes receivable	$34,000,000		$63,679,000
Fair value of notes receivable	34,000,000		63,700,000
Financial Liabilities:
Area of real estate property	7,961,288				8,735,388
Carrying Value
Financial Assets:
Carrying value of notes receivable	34,000,000	[1]	63,679,000	[1]
Financial Liabilities:
Carrying value of the debt instruments	746,866,000		813,637,000
Carrying Value | Mortgage debt
Financial Liabilities:
Carrying value of the debt instruments	303,866,000		308,637,000
Carrying Value | Unsecured term loan
Financial Liabilities:
Carrying value of the debt instruments	300,000,000		300,000,000
Carrying Value | Unsecured revolving credit facility
Financial Liabilities:
Carrying value of the debt instruments	143,000,000		205,000,000
Fair Value
Financial Assets:
Fair value of notes receivable	34,000,000	[1]	63,720,000	[1]
Financial Liabilities:
Fair value of the debt instruments	742,042,000		797,882,000
Fair Value | Mortgage debt
Financial Liabilities:
Fair value of the debt instruments	299,042,000		292,882,000
Fair Value | Unsecured term loan
Financial Liabilities:
Fair value of the debt instruments	300,000,000		300,000,000
Fair Value | Unsecured revolving credit facility
Financial Liabilities:
Fair value of the debt instruments	143,000,000		205,000,000
Richmond
Financial Liabilities:
Area of real estate property	827,900
Mortgages Held-for-sale, Fair Value Disclosure	3,500,000
America Square [Member]
Financial Liabilities:
Area of real estate property							461,000
Mezzanine loan provided to owners						$29,700,000	$30,000,000
[1]	The principal amount of our notes receivable was $34.0 million and $63.7 million at MarchB 31, 2015 and DecemberB 31, 2014, respectively.

Equity_Additional_Information_

Equity - Additional Information (Detail) (USD $)	0 Months Ended
	Jan. 27, 2015	Apr. 28, 2015
Dividends Payable [Line Items]
Dividend declared date	27-Jan-15
Series A Preferred Shares
Dividends Payable [Line Items]
Dividend paid date	17-Feb-15
Dividend record date	10-Feb-15
Dividends declared on Series A Preferred Shares	0.484375
Common Shares
Dividends Payable [Line Items]
Common share dividend per share declared	0.15
Common share dividend per share annualized	0.6
Dividend paid date	17-Feb-15
Dividend record date	10-Feb-15
Subsequent Event [Member]
Dividends Payable [Line Items]
Dividend declared date		28-Apr-15
Subsequent Event [Member] | Series A Preferred Shares
Dividends Payable [Line Items]
Dividend paid date		15-May-15
Dividend record date		8-May-15
Dividends declared on Series A Preferred Shares		0.484375
Subsequent Event [Member] | Common Shares
Dividends Payable [Line Items]
Common share dividend per share declared		0.15
Common share dividend per share annualized		0.6
Dividend paid date		15-May-15
Dividend record date		8-May-15

Equity_Companys_Allocation_Bet

Equity - Company's Allocation Between Non-controlling Interests (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$710,905	$739,291
Net income (loss)	604	-1,248
Changes in ownership, net	1,185	-1,413
Distributions to owners	-11,902	-11,889
Other comprehensive income	-1,030	168
Ending Balance	699,762	724,909
Increase (Decrease) in Temporary Equity [Roll Forward]
Beginning Balance, Redeemable noncontrolling interests	33,332	33,221
Net income (loss), Redeemable noncontrolling interests	-112	-195
Change in ownership, net, Redeemable noncontrolling interests	-581	2,067
Distributions to owners, Redeemable noncontrolling interests	-395	-393
Other comprehensive income, Redeemable noncontrolling interests	-46	7
Ending Balance, Redeemable noncontrolling interests	32,198	34,707
First Potomac Realty Trust
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	710,007	738,510
Net income (loss)	604	-1,248
Changes in ownership, net	1,281	-1,502
Distributions to owners	-11,902	-11,889
Other comprehensive income	-1,030	168
Ending Balance	698,960	724,039
Non-redeemable Noncontrolling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	898	781
Net income (loss)		0
Changes in ownership, net	-96	89
Ending Balance	$802	$870

Equity_Companys_Accumulated_Ot

Equity - Company's Accumulated Other Comprehensive Loss (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Equity [Abstract]
Beginning balance	($3,268)	($3,836)
Net unrealized (loss) gain on derivative instruments	-1,076	175
Net loss (gain) attributable to noncontrolling interests	46	-7
Ending balance	($4,298)	($3,668)

Noncontrolling_Interests_Addit

Noncontrolling Interests - Additional Information (Detail) (USD $)	3 Months Ended	0 Months Ended	3 Months Ended
	Mar. 31, 2015	Aug. 04, 2011	Mar. 31, 2014	Dec. 31, 2014	Mar. 31, 2013
	sqft	acre
Business Acquisition [Line Items]
Cost to acquire all of the outstanding common Operating Partnership units not owned by the Company	$31,300,000
Fair value adjustment, cost basis	4,200,000			4,700,000
Outstanding Operating Partnership units not owned by the Company	2,630,577
Operating Partnership units not owned by Company	4.30%
Common operating partnership units redeemed for cash	0				0
Operating Partnership units issued for acquisition	0
Area of land available for development in additional building space	1,300,000
Washington D C Reporting Segment
Business Acquisition [Line Items]
Development of area for operations by joint venture		1.6
Area of land available for development in additional building space	700,000
Projected incremental investment in development project	56,000,000
Original cost basis of the property	$43,300,000
840 First Street, NE [Member]
Business Acquisition [Line Items]
Operating Partnership units issued for acquisition			3,125
Greyhound Property [Member] | Washington D C Reporting Segment
Business Acquisition [Line Items]
Percentage of interest in joint venture		97.00%
Greyhound Property [Member] | Washington D C Reporting Segment | Maximum
Business Acquisition [Line Items]
Area of land available for development in additional building space		712,000

ShareBased_Payments_Additional

Share-Based Payments - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested share awards issued	121,380
Percentage Of Options To Be Vested On First Anniversary Of Grant Date	25.00%
Percentage Of Options To Be Vested After Date Of Grant In Each Subsequent Quarter	6.25%
Share-based Payment Award, Expiration Period	10 years 0 months 0 days
Unrecognized compensation cost related to non-vested shares	$1,400,000
Weighted-average period for recognition of non-vested shares	4 years 0 months 0 days
Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	$1.96
Employee Service Share-based Compensation, Cash Received from Exercise of Stock Options	19,000	79,000
Share-based Payment Award, Options, Exercises in Period, Intrinsic Value	5,000	18,000
Share-based Payment Award, Shares Purchased for Award	121,380
Share-based Payment Award, Weighted Average Remaining Contractual Terms	3 years 0 months 0 days
Non-Vested Share Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense associated with trustee share based awards	600,000	700,000
Unrecognized compensation cost related to non-vested shares	4,000,000
Weighted-average period for recognition of non-vested shares	2 years 3 months 24 days
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested share awards issued	119,500
Compensation expense associated with trustee share based awards	$118,000	$137,000

ShareBased_Payments_ShareBased

Share-Based Payments Share-Based Payments - Compensation Plans Option Activity (Details) (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Option, Outstanding	1,060,088		1,051,359
Option, Granted	119,500
Option, Exercised	-2,000
Option, Expired	-59,000
Option, Forfeited	-49,771
Option, Exercisable	516,839
Option, Expected to Vest this Quarter	507,651
Weighted Average Exercise Price, Outstanding	$14.67		$15.33
Weighted Average Exercise Price, Granted	$12.48
Weighted Average Exercise Price, Exercised	$9.30
Weighted Average Exercise Price, Expired	$22.44
Weighted Average Exercise Price, Forfeited	$14.48
Weighted Average Exercise Price, Exercisable	$15.52
Weighted Average Exercise Price, Expected to Vest	$13.97
Weighted Average Remaining Contractual Term, Outstanding	6 years 9 months 0 days	6 years 3 months 18 days
Weighted Average Remaining Contractual Term, Exercisable	5 years 9 months 0 days
Weighted Average Remaining Contractual Term, Expected to Vest	7 years 7 months 0 days
Aggregate Intrinsic Value, Outstanding	$107,523		$181,352
Aggregate Intrinsic Value, Exercisable	87,260
Aggregate Intrinsic Value, Expected to Vest	$17,602

ShareBased_Payments_ShareBased1

Share-Based Payments Share-Based Payments - Assumptions Used in Fair Value Determination of Stock Options Granted (Details)	3 Months Ended
	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Risk Free Interest Rate	1.61%
Expected Volatility Rate	29.16%
Expected Dividend Rate	4.79%
Expected Term	5 years 0 months 0 days

ShareBased_Payments_Summary_of

Share-Based Payments - Summary of Company's Non-vested Share Awards (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Non-vested Shares, Beginning Balance	623,421
Non-vested Shares, Granted	121,380
Non-vested Shares, Vested	-106,300
Non-vested Shares, Expired	-22,260
Non-vested Shares, Forfeited	-154,626
Non-vested Shares, Ending Balance	461,615
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted Average Grant Date Fair Value, Beginning Balance	$13.16
Weighted Average Grant Date Fair Value, Granted	$12.11
Weighted Average Grant Date Fair Value, Vested	$13.97
Weighted Average Grant Date Fair Value, Expired	$8.42
Weighted Average Grant Date Fair Value, Forfeited	$13.42
Weighted Average Grant Date Fair Value, Ending Balance	$12.83

Segment_Information_Additional

Segment Information - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2015
	segment
Segment Reporting [Abstract]
Number of Reportable Segments	4

Segment_Information_Summary_of

Segment Information - Summary of Segment Information (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
	Integer	sqft
	sqft	Integer
Segment Reporting Information [Line Items]
Number of buildings	112	137
Square feet	7,961,288	8,735,388
Total revenues	$43,849	$39,363
Property operating expense	-13,113	-12,038
Real estate taxes and insurance	-5,042	-4,132
Total property operating income	25,694	23,193
Depreciation and amortization expense	-16,335	-14,310
General and administrative	-5,526	-5,196
Acquisition costs	0	-68
Other expenses	-2,734	-4,205
Income from discontinued operations	607	857
Net income (loss)	492	-1,443
Total assets	1,534,448	1,481,336	1,618,460
Capital expenditure	19,242	11,393
Corporate assets not allocated to any reportable segments	59,450	91,673
Capital expenditures for corporate assets not allocated to any reportable segments	309	277
Washington, D.C.
Segment Reporting Information [Line Items]
Number of buildings	6	4
Square feet	916,686	522,560
Total revenues	11,032	6,940
Property operating expense	-3,139	-1,987
Real estate taxes and insurance	-2,023	-1,054
Total property operating income	5,870	3,899
Total assets	503,651	343,804
Capital expenditure	3,436	6,481
Maryland
Segment Reporting Information [Line Items]
Number of buildings	38	44
Square feet	1,999,300	2,274,813
Total revenues	11,705	11,645
Property operating expense	-4,018	-3,946
Real estate taxes and insurance	-891	-1,004
Total property operating income	6,796	6,695
Total assets	358,772	393,919
Capital expenditure	2,164	2,390
Northern Virginia
Segment Reporting Information [Line Items]
Number of buildings	49	51
Square feet	3,021,299	3,086,550
Total revenues	14,114	13,666
Property operating expense	-4,064	-3,976
Real estate taxes and insurance	-1,549	-1,524
Total property operating income	8,501	8,166
Total assets		421,556
Capital expenditure		822
Southern Virginia
Segment Reporting Information [Line Items]
Number of buildings	19	38
Square feet	2,024,003	2,851,465
Total revenues	6,998	7,112
Property operating expense	-1,892	-2,129
Real estate taxes and insurance	-579	-550
Total property operating income	4,527	4,433
Total assets	167,979	230,384
Capital expenditure	2,490	1,423
Northern Virginia
Segment Reporting Information [Line Items]
Total assets	444,596
Capital expenditure	$10,843