First Potomac Realty Trust (FPO) 10-Q 24 Oct 14 2014 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2014	Oct. 22, 2014
Document And Entity Information [Abstract]	'	'
Document Type	'10-Q	'
Amendment Flag	'false	'
Document Period End Date	30-Sep-14	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q3	'
Entity Registrant Name	'FIRST POTOMAC REALTY TRUST	'
Entity Central Index Key	'0001254595	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Large Accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	58,824,061

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Sep. 30, 2014		Dec. 31, 2013
In Thousands, unless otherwise specified
Assets:	'		'
Rental property, net	$1,342,280		$1,203,299
Assets held-for-sale	12,757		45,861
Cash and cash equivalents	11,993		8,740
Escrows and reserves	3,870		7,673
Accounts and other receivables, net of allowance for doubtful accounts of $1,440 and $1,181, respectively	11,029		12,384
Accrued straight-line rents, net of allowance for doubtful accounts of $276 and $92, respectively	31,906		30,332
Notes receivable, net	63,719		54,696
Investment in affiliates	48,008		49,150
Deferred costs, net	43,824		43,198
Prepaid expenses and other assets	8,856		8,279
Intangible assets, net	50,495		38,848
Total assets	1,628,737	[1],[2]	1,502,460
Liabilities:	'		'
Mortgage loans	301,422		274,648
Unsecured term loan	300,000		300,000
Unsecured revolving credit facility	213,000		99,000
Accounts payable and other liabilities	38,936		41,296
Accrued interest	1,743		1,663
Rents received in advance	7,158		6,118
Tenant security deposits	6,649		5,666
Deferred market rent, net	3,575		1,557
Total liabilities	872,483		729,948
Noncontrolling interests in the Operating Partnership	32,802		33,221
Equity:	'		'
Common shares, $0.001 par value, 150,000 shares authorized; 58,815 and 58,704 shares issued and outstanding, respectively	59		59
Additional paid-in capital	913,601		911,533
Noncontrolling interests in the consolidated partnership	942		781
Accumulated other comprehensive loss	-2,777		-3,836
Dividends in excess of accumulated earnings	-348,373		-329,246
Total equity	723,452		739,291
Total liabilities, noncontrolling interests and equity	1,628,737		1,502,460
Series A Preferred Stock [Member]	'		'
Equity:	'		'
Series A Preferred Shares, $25 per share liquidation preference, 6,400 shares issued and outstanding	$160,000		$160,000
[1]	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 7, Investment in Affiliates.
[2]	Corporate assets not allocated to any of our reportable segments totaled $85,238 and $112,838 at September 30, 2014 and 2013, respectively.

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified
Statement of Financial Position [Abstract]	'	'
Allowance for doubtful accounts, accounts and other receivables	$1,440	$1,181
Allowance for doubtful accounts, accrued straight-line rents	$276	$92
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	58,816,000	58,704,000
Common stock, shares outstanding	58,816,000	58,704,000

Consolidated_Statements_of_Ope

Consolidated Statements of Operations (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Revenues:	'	'	'	'
Rental	$33,432	$31,137	$98,503	$92,917
Tenant reimbursements and other	8,571	8,112	26,105	24,322
Total revenues	42,003	39,249	124,608	117,239
Operating expenses:	'	'	'	'
Property operating	11,222	10,431	34,989	30,174
Real estate taxes and insurance	4,203	4,062	12,844	12,549
General and administrative	4,955	6,346	15,370	16,598
Acquisition costs	1,488	173	2,667	173
Depreciation and amortization	16,000	14,343	46,714	42,538
Impairment of rental property	0	0	-3,956	0
Contingent consideration related to property acquisition	0	0	0	75
Total operating expenses	37,868	35,355	116,540	102,107
Operating income	4,135	3,894	8,068	15,132
Other expenses (income)	'	'	'	'
Interest expense	6,182	7,726	18,096	27,036
Interest and other income	-1,684	-1,696	-5,112	-4,800
Equity in earnings of affiliates	-412	-19	-385	-54
Gain on sale of rental property	0	0	-21,230	0
Loss on debt extinguishment / modification	0	-123	0	-324
Total other expenses (income)	4,086	6,134	-8,631	22,506
Income (loss) from continuing operations	49	-2,240	16,699	-7,374
Discontinued operations:	'	'	'	'
Income (loss) from operations	0	107	-1,096	7,147
Loss on debt extinguishment	0	0	0	-4,414
Gain on sale of rental property	0	416	1,338	19,363
Income from discontinued operations	0	523	242	22,096
Net income (loss)	49	-1,717	16,941	14,722
Less: Net loss (income) attributable to noncontrolling interests	131	211	-327	-196
Net income (loss) attributable to First Potomac Realty Trust	180	-1,506	16,614	14,526
Less: Dividends on preferred shares	-3,100	-3,100	-9,300	-9,300
Net (loss) income attributable to common shareholders	($2,920)	($4,606)	$7,314	$5,226
Basic and diluted earnings per common share:	'	'	'	'
(Loss) income from continuing operations	($0.05)	($0.09)	$0.12	($0.30)
Income from discontinued operations	$0	$0.01	$0	$0.39
Net (loss) income	($0.05)	($0.08)	$0.12	$0.09
Weighted average common shares outstanding:	'	'	'	'
Basic	58,167	57,969	58,137	54,014
Diluted	58,167	57,969	58,209	54,014

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive (Loss) Income (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]	'	'	'	'
Net income (loss)	$49	($1,717)	$16,941	$14,722
Unrealized gain on derivative instruments	1,910	157	1,231	6,051
Unrealized loss on derivative instruments	0	-1,164	-125	0
Total comprehensive income (loss)	1,959	-2,724	18,047	20,773
Net loss (income) attributable to noncontrolling interests	131	211	-327	-196
Net (gain) loss from derivative instruments attributable to noncontrolling interests	-82	43	-47	-284
Comprehensive income (loss) attributable to First Potomac Realty Trust	$2,008	($2,470)	$17,673	$20,293

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Cash flows from operating activities:	'	'
Net income	$16,941	$14,722
Discontinued operations:	'	'
Gain on sale of rental property	-1,338	-19,363
Loss on debt extinguishment	0	4,414
Depreciation and amortization	496	5,281
Impairment of rental property	0	1,921
Depreciation and amortization	47,514	43,289
Share based compensation	2,817	3,696
Bad debt expense	918	557
Amortization of deferred market rent, net	-43	29
Amortization of financing costs and discounts	1,073	2,328
Equity in earnings of affiliates	-385	-54
Distributions from investments in affiliates	1,229	1,813
Contingent consideration related to acquisition of property	0	75
Contingent consideration payments in excess of fair value at acquisition date	0	-987
Gain on sale of rental property	-21,230	0
Loss on debt extinguishment	0	324
Impairment of Real Estate	3,956	0
Changes in assets and liabilities:	'	'
Escrows and reserves	3,809	4,003
Accounts and other receivables	583	2,078
Accrued straight-line rents	-4,893	-6,267
Prepaid expenses and other assets	-736	418
Tenant security deposits	868	876
Accounts payable and accrued expenses	431	-1,605
Accrued interest	79	-956
Rents received in advance	931	-2,927
Deferred costs	-7,606	-8,242
Total adjustments	28,473	30,701
Net cash provided by operating activities	45,414	45,423
Cash flows from investing activities:	'	'
Investment in note receivable	-9,000	0
Other Payments to Acquire Businesses	0	-2,000
Proceeds from sale of rental property	85,284	213,145
Principal payments from note receivable	129	60
Change in escrow and reserve accounts	0	-28,175
Additions to rental property and furniture, fixtures and equipment	-25,464	-33,477
Additions to development and redevelopment	-9,295	-14,252
Acquisition of rental property and associated intangible assets	-150,731	0
Contributions to investment in affiliates	-1,653	-391
Distributions from investment in affiliates	1,951	0
Net cash (used in) provided by investing activities	-108,779	134,910
Cash flows from financing activities:	'	'
Financing costs	-496	-2,324
Issuance of common shares, net	0	105,085
Issuance of debt	209,794	132,199
Payment Of Deferred Acquisition Costs And Contingent Consideration	0	-9,036
Repayments of debt	-106,127	-364,367
Dividends to common shareholders	-26,391	-24,128
Dividends to preferred shareholders	-9,300	-9,300
Contributions from consolidated joint venture partners	161	250
Distributions to noncontrolling interests in the Operating Partnership	-1,183	-1,168
Operating partnership unit redemption	0	-95
Stock option exercises	160	148
Net cash provided by (used in) financing activities	66,618	-172,736
Net increase in cash and cash equivalents	3,253	7,597
Cash and cash equivalents, beginning of period	8,740	9,374
Cash and cash equivalents, end of period	11,993	16,971
Cash paid for interest, net	16,606	26,489
Non-cash investing and financing activities:	'	'
Debt assumed in connection with the acquisition of rental property	37,269	0
Value of common shares retired to settle employee income tax obligations	383	537
Change in fair value of the outstanding common Operating Partnership units	350	332
Issuance of common Operating Partnership units in connection with the acquisition of rental property	40	0
Changes in accruals:	'	'
Additions to rental property and furniture, fixtures and equipment	-290	-3,206
Additions to development and redevelopment	($782)	($974)

Consolidated_Statements_of_Cas1

Consolidated Statements of Cash Flows (Parenthetical) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2013
Capitalized interest on indebtedness paid in cash	'	$2,800,000	$1,500,000
1401 K Purchase Price	188,000,000	'	'
Mortgage Loans on Real Estate	37,300,000	37,300,000	'
Surrendered common shares to satisfy statutory minimum federal income tax obligations	400,000	'	500,000
Change in redemption value, noncontrolling interest	'	3,700,000	3,900,000
Furniture and Fixtures [Member]	'	'	'
Accrued capital expenditure	'	8,200,000	9,900,000
Development and Redevelopment [Member]	'	'	'
Accrued capital expenditure	'	800,000	3,600,000
840 First Street, NE [Member]	'	'	'
Operating Partnership units issued for acquisition	3,125	3,125	'
Operating Partnership units fair valued	$40,000	$40,000	'

Description_of_Business

Description of Business	9 Months Ended
	Sep. 30, 2014
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 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. 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.
	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 September 30, 2014, 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 September 30, 2014, we wholly-owned or had a controlling interest in properties totaling 8.9 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 approximately 1.4 million square feet of additional development. Our consolidated properties were 87.0% occupied by 581 tenants at September 30, 2014. We did not include square footage that was in development or redevelopment, which totaled 0.3 million square feet at September 30, 2014, in our occupancy calculation. We derive substantially all of our revenue from leases of space within our properties. As of September 30, 2014, our largest tenant was the U.S. Government, which along with government contractors, accounted for 26% of our total annualized cash basis rent. 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	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Summary of Significant Accounting Policies	'
	Summary of Significant Accounting Policies
	(a) Principles of Consolidation
	Our unaudited condensed consolidated financial statements include the accounts of our Company and the accounts of the 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, 2013 and as updated from time to time in other filings with the U.S. Securities and Exchange Commission (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 September 30, 2014 and the results of our operations and our comprehensive income (loss) for the three and nine months ended September 30, 2014 and 2013 and our cash flows for the nine months ended September 30, 2014 and 2013. 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 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) Application of New Accounting Standards
	In April 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update 2014-08, Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity (“ASU 2014-08”), which 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 and financial results. ASU 2014-08 is effective for fiscal years, and interim periods within those fiscal years, beginning on or after December 15, 2014. Early adoption is permitted, but only for a disposal (or classification as held-for-sale) that has not been reported in financial statements previously issued or available for issuance. ASU 2014-08 must be applied prospectively. We adopted ASU 2014-08 in the second quarter of 2014. The adoption of ASU 2014-08 did not have a material impact on our condensed consolidated financial statements, though it did and will continue to impact the extent and frequency of presenting discontinued operations within our consolidated statements of operations and note disclosures. The operations of all properties that were sold prior to the adoption of ASU 2014-08 and two other properties, West Park and Patrick Center, which were classified as held-for-sale in previously issued financial statements prior to our adoption of ASU 2014-08 and were subsequently sold, are reflected within discontinued operations in our consolidated statements of operations for all periods presented. For more information, see note 8, Dispositions. All property operations that have been classified as discontinued operations will remain classified within discontinued operations in any future presentation of our consolidated statements of operations.
	In May 2014, 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 and related disclosures.
	On August 27, 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 will not have an impact on our consolidated financial position, results of operations or cash flows.
	(d) 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 our 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 ASU 2014-08, which impacts the presentation of operations and gains or losses from disposed properties and properties classified as held-for-sale. For more information, see note 2(c), Summary of Significant Accounting Policies - Application of New Accounting Standards.
	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 related 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 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 investment 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 and nine months ended September 30, 2014 and 2013. 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.
	(e) 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 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 and nine months ended September 30, 2014 and 2013.
	(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 8, Dispositions. In the second quarter of 2014, we prospectively adopted the requirements under ASU 2014-08, which impacts the presentation of operations and gains or losses from disposed properties. For more information, see note 2(c), Summary of Significant Accounting Policies - Application of New Accounting Standards.

Earnings_Per_Common_Share

Earnings Per Common Share	9 Months Ended
	Sep. 30, 2014
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 September 30,							Nine Months Ended September 30,
		2014				2013			2014			2013
	Numerator for basic and diluted earnings per common share:
	Income (loss) from continuing operations	$	49			$	(2,240	)	$	16,699		$	(7,374	)
	Income from discontinued operations	—				523			242			22,096
	Net income (loss)	49				(1,717		)	16,941			14,722
	Less: Net loss (income) from continuing operations attributable to noncontrolling interests	131				233			(317		)	770
	Less: Net income from discontinued operations attributable to noncontrolling interests	—				(22		)	(10		)	(966		)
	Net income (loss) attributable to First Potomac Realty Trust	180				(1,506		)	16,614			14,526
	Less: Dividends on preferred shares	(3,100		)		(3,100		)	(9,300		)	(9,300		)
	Net (loss) income attributable to common shareholders	(2,920		)		(4,606		)	7,314			5,226
	Less: Allocation to participating securities	(80		)		(103		)	(235		)	(309		)
	Net (loss) income attributable to common shareholders	$	(3,000	)		$	(4,709	)	$	7,079		$	4,917
	Denominator for basic and diluted earnings per common share:
	Weighted average common shares outstanding:
	Basic	58,167				57,969			58,137			54,014
	Diluted	58,167				57,969			58,209			54,014
	Basic and diluted earnings per common share:
	(Loss) income from continuing operations	$	(0.05	)		$	(0.09	)	$	0.12		$	(0.30	)
	Income from discontinued operations	—				0.01			—			0.39
	Net (loss) income	$	(0.05	)		$	(0.08	)	$	0.12		$	0.09
	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						Nine Months Ended
		September 30,						September 30,
		2014			2013			2014		2013
	Stock option awards	1,103			1,397			1,143		1,455
	Non-vested share awards	433			513			401		528
	Series A Preferred Shares(1)	12,356			12,183			12,438		11,613
		13,892			14,093			13,982		13,596
	(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	9 Months Ended
	Sep. 30, 2014
Text Block [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, excluding properties classified as held-for-sale, consists of the following (dollars in thousands):
		September 30, 2014			December 31, 2013
	Land and land improvements	$	332,466		$	294,753
	Buildings and improvements	970,832			868,027
	Construction in process	102,618			93,269
	Tenant improvements	161,006			146,176
	Furniture, fixtures and equipment	5,153			5,047
		1,572,075			1,407,272
	Less: accumulated depreciation	(229,795		)	(203,973		)
		$	1,342,280		$	1,203,299
	Development and Redevelopment Activity
	We will place redevelopment and development assets into service at the earlier of one year after major construction activity is deemed to be substantially complete or upon occupancy. We construct office buildings and 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 1.4 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, 0.5 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 anticipate investing approximately $36 million to construct the new building, which excludes approximately $11 million of tenant improvements and approximately $2 million of combined leasing commissions and capitalized interest costs. We currently expect to complete construction of the new building in the fourth quarter of 2016. However, we can provide no assurance regarding the timing, costs or results of the project. At September 30, 2014, our total investment in the development project was $5.4 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 September 30, 2014 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 September 30, 2014, the total investment in the development project was $54.6 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 September 30, 2014, we had placed into service 38,000 square feet of the redeveloped space at the property. At September 30, 2014, our total investment in the redevelopment project was $55.4 million, which included the original cost basis of the property of $23.6 million. We will place the remaining 101,000 square feet of vacant space in-service in the fourth quarter of 2014.
	Other than the 101,000 square feet of redevelopment at 440 First Street, NW, we had no additional square feet of redevelopment yet to be placed into service at September 30, 2014. At September 30, 2014, we had no completed development that had yet to be placed into service.

Acquisitions

Acquisitions	9 Months Ended
	Sep. 30, 2014
Business Combinations [Abstract]	'
Acquisitions	'
	Acquisitions
	On September 24, 2014, we acquired 11 Dupont Circle, NW, a 153,000 square foot, nine-story, office building in downtown Washington, D.C. for $89.0 million. The acquisition was funded with a draw under our unsecured revolving credit facility.
	The fair values of the assets acquired and liabilities assumed in the 11 Dupont Circle, NW acquisition are as follows (dollars in thousands):
		30-Sep-14
	Land	$	15,835
	Acquired tenant improvements	3,374
	Building and improvements	63,957
	In-place leases	3,873
	Acquired leasing commissions	1,678
	Legal leasing fees	80
	Above-market leases acquired	1,420
	Total assets acquired	90,217
	Below-market leases assumed	(1,217		)
	Net assets acquired	$	89,000
	The fair values of the assets acquired and liabilities assumed in 2014 are preliminary as we continue to finalize their acquisition date fair value determination.
	At September 30, 2014, our consolidated intangible assets related to 11 Dupont Circle, NW in 2014 were comprised of the following categories: acquired tenant improvements; in-place leases; acquired leasing commissions; legal expenses; and above-market leases, which had an aggregate weighted average amortization period of 5.6 years.
	During the second quarter of 2014, we acquired the following properties (dollars in thousands):
	Property	Reporting Segment	Acquisition Date	Property Type	Square Feet	Contractual Purchase Price
	1401 K Street, NW(1)	Washington, DC	8-Apr-14	Office	117,378	$58,000
	1775 Wiehle Avenue	Northern Virginia	25-Jun-14	Office	130,048	$41,000
	(1)	The purchase price for 1401 K Street, NW includes the assumption of a $37.3 million mortgage loan.
	For the three and nine months ended September 30, 2014, we included $2.7 million and $4.0 million of revenues, and $0.4 million and $1.1 million of net loss, respectively, in our consolidated statements of operations related to the acquisition of 1401 K Street, NW, 1775 Wiehle Avenue and 11 Dupont Circle, NW. We incurred $1.5 million and $2.7 million of acquisition-related due diligence and closing costs during the three and nine months ended September 30, 2014, respectively, and $0.2 million for both the three and nine months ended September 30, 2013.
	Pro Forma Financial Information (unaudited)
	The unaudited pro forma financial information set forth below presents results for the nine months ended September 30, 2014 and 2013 as if the acquisitions of 1401 K Street, NW, 1775 Wiehle Avenue and 11 Dupont Circle, NW had occurred on January 1, 2013. The pro forma information is not necessarily indicative of the results that actually would have occurred nor does it intend to indicate future operating results (dollars in thousands, except per share amounts):
		2014				2013
	Pro forma total revenues	$	136,743			$	133,411
	Pro forma net income	$	19,691			$	9,914
	Pro forma net income per share - basic and diluted	$	0.17			$	0.01

Notes_Receivable

Notes Receivable	9 Months Ended
	Sep. 30, 2014
Receivables [Abstract]	'
Notes Receivable	'
	Notes Receivable
	Below is a summary of our notes receivable (dollars in thousands):
	Balance at September 30, 2014
	Face Amount		Unamortized			Balance		Interest Rate		Property
			Origination Fees
	$	34,000	$	—		$	34,000	9.75	%	950 F Street, NW
	29,767		(48		)	29,719		9	%	America’s Square
	$	63,767	$	(48	)	$	63,719
	Balance at December 31, 2013
	Face Amount		Unamortized			Balance		Interest Rate		Property
			Origination Fees
	$	25,000	$	(130	)	$	24,870	12.5	%	950 F Street, NW
	29,896		(70		)	29,826		9	%	America’s Square
	$	54,896	$	(200	)	$	54,696
	In April 2011, we provided a $30.0 million mezzanine loan to the owners of America’s Square, a 461,000 square-foot office complex located in Washington, D.C. that is secured by a portion of the owners’ interest in the property. The loan is repayable in full at any time, subject to yield maintenance. The loan matures on May 1, 2016 and required monthly interest-only payments until May 2013, at which time the loan began requiring monthly principal and interest payments through its maturity date. The interest rate on the loan is constant throughout the life of the loan.
	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.
	We recorded interest income of $1.5 million and $4.5 million related to our notes receivable for the three and nine months ended September 30, 2014, respectively, and $1.5 million and $4.4 million for the three and nine months ended September 30, 2013, 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 $7 thousand and $25 thousand for the three and nine months ended September 30, 2014, respectively, and $17 thousand and $52 thousand for the three and nine months ended September 30, 2013, 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. 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	9 Months Ended
	Sep. 30, 2014
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			30-Sep-14			December 31, 2013
				Interest
	Prosperity Metro Plaza	Northern Virginia		51	%		$	25,466		$	24,735
	1750 H Street, NW	Washington, D.C.		50	%		14,732			16,780
	Aviation Business Park	Maryland		50	%		5,524			5,008
	RiversPark I and II(1)	Maryland		25	%		2,286			2,627
							$	48,008		$	49,150
	(1) RiversPark I and RiversPark II are owned through two separate joint ventures.
	The net assets of our unconsolidated joint ventures consisted of the following (dollars in thousands):
		September 30, 2014				December 31, 2013
	Assets:
	Rental property, net	$	194,075			$	194,240
	Cash and cash equivalents	3,686				3,680
	Other assets	17,529				15,585
	Total assets	215,290				213,505
	Liabilities:
	Mortgage loans(1)(2)	108,456				106,384
	Other liabilities	7,793				5,046
	Total liabilities	116,249				111,430
	Net assets	$	99,041			$	102,075
	(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.
	(2)	Includes the unamortized fair value adjustments recorded at acquisition upon the assumption of mortgage loans.
	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.
	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.
	Our share of earnings or losses related to our unconsolidated joint ventures is recorded in our consolidated statements of operations as “Equity in earnings 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							Nine Months Ended
		September 30,							September 30,
		2014				2013			2014			2013
	Total revenues	$	5,713			$	6,035		$	17,245		$	18,046
	Total operating expenses	(1,818		)		(1,879		)	(5,738		)	(5,649		)
	Net operating income	3,895				4,156			11,507			12,397
	Depreciation and amortization	(2,256		)		(2,887		)	(7,323		)	(8,681		)
	Other expenses, net	(890		)		(1,091		)	(2,978		)	(3,254		)
	Net income	$	749			$	178		$	1,206		$	462
	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 $0.2 million and $0.5 million for the three and nine months ended September 30, 2014 and 2013, respectively, which are reflected within “Tenant reimbursements and other revenues” in our consolidated statements of operations.

Dispositions

Dispositions	9 Months Ended
	Sep. 30, 2014
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. For more information, see note 2(c), Summary of Significant Accounting Policies - Application of New Accounting Standards.
	(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:
		Reporting	Disposition Date	Property Type	Square Feet
		Segment
	Owings Mills Business Park	Maryland	10/16/14	Business Park	180,475
	Corporate Campus at Ashburn Center	Northern Virginia	6/26/14	Business Park	194,184
	On October 16, 2014, we sold the four remaining buildings at Owings Mills Business Park for net proceeds of $12.4 million. We recorded an impairment charge of $4.0 million in the second quarter of 2014. We had previously sold two buildings at Owings Mills Business Park in 2012. At September 30, 2014, the four buildings at Owings Mills Business Park met our held-for-sale criteria and, therefore, the assets of the buildings were classified within “Assets held-for-sale” and the liabilities of the buildings, which totaled $0.2 million, were classified within “Accounts payable and other liabilities” in our consolidated balance sheet. The majority of the assets classified within “Assets held-for sale” as of September 30, 2014, consisted of $2.7 million in land, $11.8 million in building, $1.5 million in tenant improvements and accumulated depreciation of $3.5 million.  The remaining $0.3 million classified within “Assets held-for sale” consisted of accrued straight-line rents, net of allowance for doubtful accounts, deferred costs, net of accumulated amortization, and prepaid expenses and other assets.
	In accordance with ASU 2014-08, which we prospectively adopted during the second quarter of 2014, the operating results and gain on sale of Corporate Campus at Ashburn Center and the operating results and impairment of Owings Mills Business Park are reflected in continuing operations in our consolidated statements of operations for each of the periods presented. The following table summarizes the aggregate results of operations for two properties that are included in continuing operations for the periods presented (dollars in thousands):
		Three Months Ended							Nine Months Ended September 30,
		September 30,
		2014				2013			2014			2013
	Revenues	$	119			$	1,317		$	2,914		$	3,959
	Property operating expenses	(155		)		(364		)	(1,104		)	(1,137		)
	Depreciation and amortization	(209		)		(349		)	(977		)	(1,050		)
	Impairment of rental property	—				—			(3,956		)	—
	(Loss) income from operations of disposed property	(245		)		604			(3,123		)	1,772
	Gain on sale of rental property	—				—			21,230			—
	Net (loss) income from continuing operations	$	(245	)		$	604		$	18,107		$	1,772
	(b) Discontinued Operations
	All properties classified within discontinued operations were 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.
	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:
		Reporting	Disposition Date	Property Type	Square Feet
		Segment
	Patrick Center	Maryland	4/16/14	Office	66,269
	West Park	Maryland	4/2/14	Office	28,333
	Girard Business Center and Gateway Center	Maryland	1/29/14	Business Park and Office	341,973
	Worman’s Mill Court	Maryland	11/19/13	Office	40,099
	Triangle Business Center	Maryland	9/27/13	Business Park	74,429
	4200 Tech Court	Northern Virginia	8/15/13	Office	33,875
	Industrial Portfolio(1)	Various	May/June 2013	Industrial	4,280,985
	4212 Tech Court	Northern Virginia	6/5/13	Office	32,055
	(1)	During the second quarter of 2013, we sold 24 industrial properties, which consisted of two separate transactions. On May 7, 2013, we sold I-66 Commerce Center, a 236,000 square foot industrial property in Haymarket, Virginia. On June 18, 2013, we completed the sale of the remaining 23 industrial properties.
	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 nine months ended September 30, 2014 and 2013.
	The following table summarizes the results of operations of properties included in discontinued operations (dollars in thousands):
		Three Months Ended							Nine Months Ended
		September 30,							September 30,
		2014				2013			2014			2013
	Revenues	$	—			$	1,907		$	867		$	22,081
	Net income (loss), before taxes(1)	—				107			(1,096		)	2,733
	Gain on sale of rental property	—				416			1,338			19,363
	(1)	During the first quarter of 2014, we accelerated $1.0 million of unamortized straight-line rent and deferred abatement costs related to the sale of Girard Business Center and Gateway Center.

Debt

Debt	9 Months Ended
	Sep. 30, 2014
Debt Disclosure [Abstract]	'
Debt	'
	Debt
	Our borrowings consisted of the following (dollars in thousands):
		September 30,				December 31,
		2014				2013
	Mortgage loans, effective interest rates ranging from 4.40% to 6.63%, maturing at various dates through June 2023(1)	$	301,422			$	274,648
	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(1)	300,000				300,000
	Unsecured revolving credit facility, effective interest rate of LIBOR plus 1.50%, maturing October 2017(1)	213,000				99,000
		$	814,422			$	673,648
	(1)	At September 30, 2014, LIBOR was 0.16%. 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 September 30, 2014 and December 31, 2013 (dollars in thousands):
	Encumbered Property	Contractual		Effective			Maturity		September 30,			December 31,
		Interest Rate		Interest			Date		2014			2013
				Rate
	Annapolis Business Center(1)	5.74%		6.25	%		Jun-14		$	—		$	8,076
	Storey Park(2)(3)	LIBOR + 2.75%		5.8	%		Oct-14		22,000			22,000
	Jackson National Life Loan(4)	5.19%		5.19	%		Aug-15		65,242			66,116
	Hanover Business Center Building D	8.88%		6.63	%		Aug-15		142			252
	Chesterfield Business Center Buildings C, D, G and H	8.50%		6.63	%		Aug-15		399			681
	440 First Street, NW Construction Loan(2)	LIBOR + 2.50%		4.78	%		May-16		23,493			21,699
	Gateway Centre Manassas Building I	7.35%		5.88	%		November 2016		484			638
	Hillside I and II	5.75%		4.62	%		Dec-16		13,051			13,349
	Redland Corporate Center Buildings II & III	4.20%		4.64	%		Nov-17		66,127			67,038
	Hanover Business Center Building C	7.88%		6.63	%		Dec-17		543			653
	840 First Street, NE	5.72%		6.01	%		Jul-20		36,694			37,151
	Battlefield Corporate Center	4.26%		4.4	%		Nov-20		3,732			3,851
	Chesterfield Business Center Buildings A,B,E and F	7.45%		6.63	%		Jun-21		1,725			1,873
	Airpark Business Center	7.45%		6.63	%		Jun-21		941			1,022
	1211 Connecticut Avenue, NW	4.22%		4.47	%		Jul-22		29,833			30,249
	1401 K Street, NW	4.80%		4.93	%		Jun-23		37,016			—
				5.06	%	(5)			301,422			274,648
	Unamortized fair value adjustments								(500		)	(663		)
	Total contractual principal balance								$	300,922		$	273,985
	(1)	The loan was prepaid, without penalty, on May 1, 2014 with borrowings under our unsecured revolving credit facility.
	(2)	At September 30, 2014, LIBOR was 0.16%.
	(3)	The loan was repaid on October 16, 2014. Simultaneously with the repayment, our 97% owned consolidated joint venture entered into a new $22.0 million land loan with an applicable interest rate of LIBOR plus 2.50%, which matures on October 16, 2016, with a one-year extension at our option.
	(4)	At September 30, 2014, 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)	Weighted average interest rate on total mortgage debt.
	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.
	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 the second quarter of 2013 and borrowed an additional $1.8 million in January 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 September 30, 2014, 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 September 30, 2014, 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 September 30, 2014 (dollars in thousands):
		Maturity Date		Amount				Interest Rate(1)
	Tranche A	October 2018		$	100,000			LIBOR, plus 145 basis points
	Tranche B	October 2019		100,000				LIBOR, plus 160 basis points
	Tranche C	October 2020		100,000				LIBOR, plus 190 basis points
				$	300,000
	(1)	At September 30, 2014, LIBOR was 0.16%. The interest rate spread is subject to change based on our maximum total indebtedness ratio. Based on our maximum total indebtedness ratio at September 30, 2014, the applicable interest rate spreads on Tranche A, Tranche B and Tranche C of the unsecured term loan will increase by 20 basis points, 20 basis points and 15 basis points, respectively, in November 2014. For more information, see note 9(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 September 30, 2014, we were in compliance with all the financial covenants of the unsecured term loan.
	(c) Unsecured Revolving Credit Facility
	During the third quarter of 2014, we borrowed $105.0 million under the unsecured revolving credit facility, of which $89.0 million was used to fund the acquisition of 11 Dupont Circle, NW and $16.0 million was used for general corporate purposes. During the third quarter of 2014, we repaid an additional $8.0 million of the outstanding balance under the unsecured revolving credit facility with our portion of the proceeds from the new 1750 H Street, NW mortgage loan and available cash. For the three and nine months ended September 30, 2014, our weighted average borrowings under the unsecured revolving credit facility were $125.9 million and $112.0 million, respectively, with a weighted average interest rate of 1.6% and 1.7%, respectively, compared with weighted average borrowings of $50.4 million and $154.9 million, with a weighted average interest rate of 2.6% and 2.8%, respectively, for the three and nine months ended September 30, 2013, respectively. Our maximum outstanding borrowings were $216.0 million for both the three and nine months ended September 30, 2014 compared with $83.0 million and $245.0 million for the three and nine months ended September 30, 2013, respectively. At September 30, 2014, outstanding borrowings under the unsecured revolving credit facility were $213.0 million with a weighted average interest rate of 1.7%. At September 30, 2014, LIBOR was 0.16% and the applicable spread on our unsecured revolving credit facility was 150 basis points. The available capacity under the unsecured revolving credit facility was $97.1 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. Based on our leverage ratio at September 30, 2014, the applicable interest rate spread on the unsecured revolving credit facility will increase by 20 basis points in November 2014. For more information, see note 9(e) Debt – Financial Covenants. As of September 30, 2014, we were in compliance with all the financial covenants of the unsecured revolving credit facility.
	(d) Interest Rate Swap Agreements
	At September 30, 2014, we fixed LIBOR, at a weighted average interest rate of 1.5%, on $300.0 million of our variable rate debt through eleven interest rate swap agreements. See note 10, 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 September 30, 2014, 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).
	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 September 30, 2014, the applicable interest rate spread on the unsecured revolving credit facility will increase by 20 basis points and the applicable interest rate spreads on Tranche A, Tranche B and Tranche C of our unsecured term loan will increase by 20 basis points, 20 basis points and 15 basis points, respectively, in November 2014.

Derivative_Instruments

Derivative Instruments	9 Months Ended
	Sep. 30, 2014
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 exposure 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 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 our 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 September 30, 2014, we fixed LIBOR at a weighted average interest rate of 1.5% on $300.0 million of our variable rate debt through eleven interest rate swap agreements that are summarized below (dollars in thousands):
	Effective Date		Maturity Date	Notional	Interest Rate	Fixed LIBOR
				Amount	Contractual	Interest Rate
					Component
	Jul-11		Jul-16	$35,000	LIBOR	1.75%
	Jul-11		Jul-16	25,000	LIBOR	1.76%
	Jul-11		Jul-17	30,000	LIBOR	2.09%
	Jul-11		Jul-17	30,000	LIBOR	2.09%
	Sep-11		Jul-18	30,000	LIBOR	1.66%
	Jan-12		Jul-18	25,000	LIBOR	1.39%
	Mar-12		Jul-17	25,000	LIBOR	1.13%
	Mar-12		Jul-17	12,500	LIBOR	1.13%
	Mar-12		Jul-18	12,500	LIBOR	1.38%
	Jun-12		Jul-17	50,000	LIBOR	0.96%
	Jun-12		Jul-18	25,000	LIBOR	1.14%
			Total/Weighted Average	$300,000		1.51%
	Our interest rate swap agreements are designated as cash flow hedges and we record 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 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 and nine months ended September 30, 2014 and 2013.
	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 and $1.2 million for the three months ended September 30, 2014 and 2013, respectively, and $3.1 million and $3.5 million for the nine months ended September 30, 2014 and 2013, respectively. As of September 30, 2014, we estimated that $2.8 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	9 Months Ended
	Sep. 30, 2014
Fair Value Disclosures [Abstract]	'
Fair Value Measurements	'
	Fair Value Measurements
	We apply GAAP that 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 September 30, 2014 and December 31, 2013 (dollars in thousands):
		Balance at		Level 1		Level 2		Level 3
		September 30, 2014
	Non-recurring Measurements:
	Impaired real estate assets	$	12,500	$	—	$	12,500	$	—
	Recurring Measurements:
	Derivative instrument-swap assets	451		—		451		—
	Derivative instrument-swap liabilities	3,371		—		3,371		—
		Balance at		Level 1		Level 2		Level 3
		December 31, 2013
	Non-recurring Measurements:
	Impaired real estate assets	$	2,909	$	—	$	2,909	$	—
	Recurring Measurements:
	Derivative instrument-swap assets	551		—		551		—
	Derivative instrument-swap liabilities	4,576		—		4,576		—
	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 and nine months ended September 30, 2014 and 2013. 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 nine months ended September 30, 2014 and 2013.
	Impairment of Real Estate Assets
	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 a property, an impairment analysis is performed.
	On October 16, 2014, we sold the four remaining buildings at Owings Mills Business Park, which was located in our Maryland reporting segment. Based on the anticipated sales price of the four buildings that were subsequently sold, we recorded an impairment charge of $4.0 million in the second quarter of 2014.
	Interest Rate Derivatives
	The interest rate derivatives are fair valued based on prevailing market yield curves on the measurement date and also take into consideration the credit valuation adjustment of the counter-party in determining the fair value of counterparty credit risk associated with our interest rate swap agreements. 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 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 value and estimated fair value of our financial assets and liabilities are as follows (dollars in thousands):
		September 30, 2014				December 31, 2013
		Carrying		Fair		Carrying		Fair
		Value		Value		Value		Value
	Financial Assets:
	Notes receivable(1)	$	63,719	$	63,767	$	54,696	$	56,812
	Financial Liabilities:
	Mortgage debt	$	301,422	$	289,647	$	274,648	$	262,873
	Unsecured term loan	300,000		300,000		300,000		300,000
	Unsecured revolving credit facility	213,000		213,000		99,000		99,000
	Total	$	814,422	$	802,647	$	673,648	$	661,873
	(1)	The principal amount of our notes receivable was $63.8 million and $54.9 million at September 30, 2014 and December 31, 2013, respectively. On January 10, 2014, we amended the 950 F Street, NW mezzanine loan and increased the outstanding balance to $34.0 million.

Equity

Equity	9 Months Ended
	Sep. 30, 2014
Equity [Abstract]	'
Equity	'
	Equity
	On October 21, 2014, 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 November 17, 2014 to common shareholders of record as of November 6, 2014. We also declared a dividend of $0.484375 per share on our Series A Preferred Shares. The dividend will be paid on November 17, 2014 to preferred shareholders of record as of November 6, 2014.
	On July 22, 2014, 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 August 15, 2014 to common shareholders of record as of August 6, 2014. We also declared a dividend of $0.484375 per share on our Series A Preferred Shares. The dividend was paid on August 15, 2014 to preferred shareholders of record as of August 6, 2014. 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.
	Our unsecured revolving credit facility, unsecured term loan and the Construction Loan contain certain restrictions that include, among other things, requirements to maintain specified coverage ratios and other financial covenants, which may limit our Company’s 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, 2013	$	738,510		$	781		$	739,291		$	33,221
	Net income	16,614			—			16,614			327
	Changes in ownership, net	2,018			161			2,179			390
	Distributions to owners	(35,691		)	—			(35,691		)	(1,183		)
	Other comprehensive income	1,059			—			1,059			47
	Balance at September 30, 2014	$	722,510		$	942		$	723,452		$	32,802
		First			Non-redeemable			Total Equity			Redeemable
		Potomac			noncontrolling						noncontrolling
		Realty Trust			interests						interests
	Balance at December 31, 2012	$	658,765		$	3,728		$	662,493		$	34,367
	Net income (loss)	14,526			(20		)	14,506			216
	Changes in ownership, net	107,836			249			108,085			273
	Distributions to owners	(33,428		)	—			(33,428		)	(1,168		)
	Other comprehensive income	5,767			—			5,767			284
	Balance at September 30, 2013	$	753,466		$	3,957		$	757,423		$	33,972
	A summary of our accumulated other comprehensive loss is as follows (dollars in thousands):
		2014			2013
	Beginning balance at January1,	$	(3,836	)	$	(10,917	)
	Net unrealized gain on derivative instruments	1,106			6,051
	Net gain attributable to noncontrolling interests	(47		)	(284		)
	Ending balance at September 30,	$	(2,777	)	$	(5,150	)

Noncontrolling_Interests

Noncontrolling Interests	9 Months Ended
	Sep. 30, 2014
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 September 30, 2014, 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 $30.9 million. At September 30, 2014 and December 31, 2013, we recorded adjustments of $3.7 million and $3.3 million, respectively, to present certain common Operating Partnership units at the greater of their carrying value or redemption value.
	At December 31, 2013, 2,627,452 of the total common Operating Partnership units, or 4.3%, were not owned by us. During the first quarter of 2014, we issued 3,125 common Operating Partnership units at a fair value of $40 thousand to the seller of 840 First Street, NE to satisfy our contingent consideration obligation related to the acquisition of the property. As a result, 2,630,577 of the total common Operating Partnership units, or 4.3%, were not owned by us at September 30, 2014. There were no common Operating Partnership units redeemed for common shares or cash during the nine months ended September 30, 2014.
	(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 (income) 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 September 30, 2014, the total investment in the development project was $54.6 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.

Segment_Information

Segment Information	9 Months Ended
	Sep. 30, 2014
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 and nine months ended September 30, 2014 and 2013 are as follows (dollars in thousands):
		Three Months Ended September 30, 2014
		Washington, D.C.(1)			Maryland			Northern Virginia			Southern Virginia			Consolidated
	Number of buildings	6			42			49			38			135
	Square feet	815,093			2,179,366			3,020,975			2,852,212			8,867,646
	Total revenues	$	8,489		$	11,154		$	13,309		$	9,051		$	42,003
	Property operating expense	(2,496		)	(2,540		)	(3,121		)	(3,065		)	(11,222		)
	Real estate taxes and insurance	(1,278		)	(956		)	(1,228		)	(741		)	(4,203		)
	Total property operating income	$	4,715		$	7,658		$	8,960		$	5,245		$	26,578
	Depreciation and amortization expense													(16,000		)
	General and administrative													(4,955		)
	Acquisition costs													(1,488		)
	Other expenses													(4,086		)
	Net income													$	49
	Capital expenditures(2)	$	5,320		$	1,875		$	1,516		$	2,001		$	10,767
		Three Months Ended September 30, 2013
		Washington, D.C.(3)			Maryland			Northern Virginia			Southern Virginia			Consolidated
	Number of buildings	3			53			51			38			145
	Square feet	502,690			2,544,481			3,085,740			2,852,240			8,985,151
	Total revenues	$	6,963		$	10,207		$	13,231		$	8,848		$	39,249
	Property operating expense	(1,591		)	(2,775		)	(3,088		)	(2,977		)	(10,431		)
	Real estate taxes and insurance	(1,151		)	(837		)	(1,372		)	(702		)	(4,062		)
	Total property operating income	$	4,221		$	6,595		$	8,771		$	5,169		$	24,756
	Depreciation and amortization expense													(14,343		)
	General and administrative													(6,346		)
	Acquisition costs													(173		)
	Other expenses													(6,134		)
	Income from discontinued operations													523
	Net loss													$	(1,717	)
	Capital expenditures(2)	$	4,758		$	2,662		$	2,798		$	1,979		$	12,609
		Nine Months Ended September 30, 2014
		Washington, D.C.(1)			Maryland			Northern Virginia			Southern Virginia			Consolidated
	Total revenues	$	23,256		$	34,025		$	40,122		$	27,205		$	124,608
	Property operating expense	(6,889		)	(8,913		)	(10,203		)	(8,984		)	(34,989		)
	Real estate taxes and insurance	(3,579		)	(2,934		)	(4,217		)	(2,114		)	(12,844		)
	Total property operating income	$	12,788		$	22,178		$	25,702		$	16,107		$	76,775
	Depreciation and amortization expense													(46,714		)
	General and administrative													(15,370		)
	Acquisition costs													(2,667		)
	Impairment of rental property													(3,956		)
	Other income													8,631
	Income from discontinued operations													242
	Net income													$	16,941
	Total assets(4)(5)	$	501,536		$	375,399		$	437,909		$	228,655		$	1,628,737
	Capital expenditures(2)	$	16,702		$	6,966		$	3,876		$	6,173		$	34,410
		Nine Months Ended September 30, 2013
		Washington, D.C.(3)			Maryland			Northern Virginia			Southern Virginia			Consolidated
	Total revenues	$	21,730		$	30,828		$	38,589		$	26,092		$	117,239
	Property operating expense	(4,831		)	(7,873		)	(9,222		)	(8,248		)	(30,174		)
	Real estate taxes and insurance	(3,746		)	(2,473		)	(4,302		)	(2,028		)	(12,549		)
	Total property operating income	$	13,153		$	20,482		$	25,065		$	15,816		$	74,516
	Depreciation and amortization expense													(42,538		)
	General and administrative													(16,598		)
	Acquisition costs													(173		)
	Contingent consideration related to acquisition of property													(75		)
	Other expenses													(22,506		)
	Income from discontinued operations													22,096
	Net income													$	14,722
	Total assets(4)(5)	$	334,427		$	406,789		$	426,839		$	230,390		$	1,511,283
	Capital expenditures(2)	$	17,543		$	10,597		$	11,100		$	7,513		$	47,729
	(1)	Includes occupied space at 440 First Street, NW and excludes Storey Park, which was placed in development in the third quarter of 2013.
(2)	Capital expenditures for corporate assets not allocated to any of our reportable segments totaled $55 and $412 for the three months ended September 30, 2014 and 2013, respectively, and $693 and $976 for the nine months ended September 30, 2014 and 2013, respectively.
(3)	Excludes 440 First Street, NW, which has been in redevelopment since its acquisition in 2010.
(4)	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 7, Investment in Affiliates.
(5)	Corporate assets not allocated to any of our reportable segments totaled $85,238 and $112,838 at September 30, 2014 and 2013, respectively.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Principles of Consolidation	'
	Principles of Consolidation
	Our unaudited condensed consolidated financial statements include the accounts of our Company and the accounts of the 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, 2013 and as updated from time to time in other filings with the U.S. Securities and Exchange Commission (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 September 30, 2014 and the results of our operations and our comprehensive income (loss) for the three and nine months ended September 30, 2014 and 2013 and our cash flows for the nine months ended September 30, 2014 and 2013. 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 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.
Application of New Accounting Standards	'
	Application of New Accounting Standards
	In April 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update 2014-08, Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity (“ASU 2014-08”), which 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 and financial results. ASU 2014-08 is effective for fiscal years, and interim periods within those fiscal years, beginning on or after December 15, 2014. Early adoption is permitted, but only for a disposal (or classification as held-for-sale) that has not been reported in financial statements previously issued or available for issuance. ASU 2014-08 must be applied prospectively. We adopted ASU 2014-08 in the second quarter of 2014. The adoption of ASU 2014-08 did not have a material impact on our condensed consolidated financial statements, though it did and will continue to impact the extent and frequency of presenting discontinued operations within our consolidated statements of operations and note disclosures. The operations of all properties that were sold prior to the adoption of ASU 2014-08 and two other properties, West Park and Patrick Center, which were classified as held-for-sale in previously issued financial statements prior to our adoption of ASU 2014-08 and were subsequently sold, are reflected within discontinued operations in our consolidated statements of operations for all periods presented. For more information, see note 8, Dispositions. All property operations that have been classified as discontinued operations will remain classified within discontinued operations in any future presentation of our consolidated statements of operations.
	In May 2014, 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 and related disclosures.
	On August 27, 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 will not have an impact on our consolidated financial position, results of operations or cash flows.
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 our 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 ASU 2014-08, which impacts the presentation of operations and gains or losses from disposed properties and properties classified as held-for-sale. For more information, see note 2(c), Summary of Significant Accounting Policies - Application of New Accounting Standards.
	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 related 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 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 investment 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 and nine months ended September 30, 2014 and 2013. 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 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 and nine months ended September 30, 2014 and 2013.
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 8, Dispositions. In the second quarter of 2014, we prospectively adopted the requirements under ASU 2014-08, which impacts the presentation of operations and gains or losses from disposed properties. For more information, see note 2(c), Summary of Significant Accounting Policies - Application of New Accounting Standards.

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2014
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)	9 Months Ended
	Sep. 30, 2014
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 September 30,							Nine Months Ended September 30,
		2014				2013			2014			2013
	Numerator for basic and diluted earnings per common share:
	Income (loss) from continuing operations	$	49			$	(2,240	)	$	16,699		$	(7,374	)
	Income from discontinued operations	—				523			242			22,096
	Net income (loss)	49				(1,717		)	16,941			14,722
	Less: Net loss (income) from continuing operations attributable to noncontrolling interests	131				233			(317		)	770
	Less: Net income from discontinued operations attributable to noncontrolling interests	—				(22		)	(10		)	(966		)
	Net income (loss) attributable to First Potomac Realty Trust	180				(1,506		)	16,614			14,526
	Less: Dividends on preferred shares	(3,100		)		(3,100		)	(9,300		)	(9,300		)
	Net (loss) income attributable to common shareholders	(2,920		)		(4,606		)	7,314			5,226
	Less: Allocation to participating securities	(80		)		(103		)	(235		)	(309		)
	Net (loss) income attributable to common shareholders	$	(3,000	)		$	(4,709	)	$	7,079		$	4,917
	Denominator for basic and diluted earnings per common share:
	Weighted average common shares outstanding:
	Basic	58,167				57,969			58,137			54,014
	Diluted	58,167				57,969			58,209			54,014
	Basic and diluted earnings per common share:
	(Loss) income from continuing operations	$	(0.05	)		$	(0.09	)	$	0.12		$	(0.30	)
	Income from discontinued operations	—				0.01			—			0.39
	Net (loss) income	$	(0.05	)		$	(0.08	)	$	0.12		$	0.09
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						Nine Months Ended
		September 30,						September 30,
		2014			2013			2014		2013
	Stock option awards	1,103			1,397			1,143		1,455
	Non-vested share awards	433			513			401		528
	Series A Preferred Shares(1)	12,356			12,183			12,438		11,613
		13,892			14,093			13,982		13,596
	(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)	9 Months Ended
	Sep. 30, 2014
Text Block [Abstract]	'
Summary of Rental Property	'
	Rental property, excluding properties classified as held-for-sale, consists of the following (dollars in thousands):
		September 30, 2014			December 31, 2013
	Land and land improvements	$	332,466		$	294,753
	Buildings and improvements	970,832			868,027
	Construction in process	102,618			93,269
	Tenant improvements	161,006			146,176
	Furniture, fixtures and equipment	5,153			5,047
		1,572,075			1,407,272
	Less: accumulated depreciation	(229,795		)	(203,973		)
		$	1,342,280		$	1,203,299

Acquisitions_Tables

Acquisitions (Tables)	9 Months Ended
	Sep. 30, 2014
Business Combinations [Abstract]	'
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	'
	The fair values of the assets acquired and liabilities assumed in the 11 Dupont Circle, NW acquisition are as follows (dollars in thousands):
		30-Sep-14
	Land	$	15,835
	Acquired tenant improvements	3,374
	Building and improvements	63,957
	In-place leases	3,873
	Acquired leasing commissions	1,678
	Legal leasing fees	80
	Above-market leases acquired	1,420
	Total assets acquired	90,217
	Below-market leases assumed	(1,217		)
	Net assets acquired	$	89,000
Schedule of Business Acquisitions, by Acquisition [Table Text Block]	'
	During the second quarter of 2014, we acquired the following properties (dollars in thousands):
	Property	Reporting Segment	Acquisition Date	Property Type	Square Feet	Contractual Purchase Price
	1401 K Street, NW(1)	Washington, DC	8-Apr-14	Office	117,378	$58,000
	1775 Wiehle Avenue	Northern Virginia	25-Jun-14	Office	130,048	$41,000
	(1)	The purchase price for 1401 K Street, NW includes the assumption of a $37.3 million mortgage loan.
Business Acquisition, Pro Forma Information	'
	The pro forma information is not necessarily indicative of the results that actually would have occurred nor does it intend to indicate future operating results (dollars in thousands, except per share amounts):
		2014				2013
	Pro forma total revenues	$	136,743			$	133,411
	Pro forma net income	$	19,691			$	9,914
	Pro forma net income per share - basic and diluted	$	0.17			$	0.01

Notes_Receivable_Tables

Notes Receivable (Tables)	9 Months Ended
	Sep. 30, 2014
Receivables [Abstract]	'
Summary of Notes Receivable	'
	Below is a summary of our notes receivable (dollars in thousands):
	Balance at September 30, 2014
	Face Amount		Unamortized			Balance		Interest Rate		Property
			Origination Fees
	$	34,000	$	—		$	34,000	9.75	%	950 F Street, NW
	29,767		(48		)	29,719		9	%	America’s Square
	$	63,767	$	(48	)	$	63,719
	Balance at December 31, 2013
	Face Amount		Unamortized			Balance		Interest Rate		Property
			Origination Fees
	$	25,000	$	(130	)	$	24,870	12.5	%	950 F Street, NW
	29,896		(70		)	29,826		9	%	America’s Square
	$	54,896	$	(200	)	$	54,696

Investment_in_Affiliates_Table

Investment in Affiliates (Tables)	9 Months Ended
	Sep. 30, 2014
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			30-Sep-14			December 31, 2013
				Interest
	Prosperity Metro Plaza	Northern Virginia		51	%		$	25,466		$	24,735
	1750 H Street, NW	Washington, D.C.		50	%		14,732			16,780
	Aviation Business Park	Maryland		50	%		5,524			5,008
	RiversPark I and II(1)	Maryland		25	%		2,286			2,627
							$	48,008		$	49,150
	(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):
		September 30, 2014				December 31, 2013
	Assets:
	Rental property, net	$	194,075			$	194,240
	Cash and cash equivalents	3,686				3,680
	Other assets	17,529				15,585
	Total assets	215,290				213,505
	Liabilities:
	Mortgage loans(1)(2)	108,456				106,384
	Other liabilities	7,793				5,046
	Total liabilities	116,249				111,430
	Net assets	$	99,041			$	102,075
	(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.
	(2)	Includes the unamortized fair value adjustments recorded at acquisition upon the assumption of mortgage loans.
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							Nine Months Ended
		September 30,							September 30,
		2014				2013			2014			2013
	Total revenues	$	5,713			$	6,035		$	17,245		$	18,046
	Total operating expenses	(1,818		)		(1,879		)	(5,738		)	(5,649		)
	Net operating income	3,895				4,156			11,507			12,397
	Depreciation and amortization	(2,256		)		(2,887		)	(7,323		)	(8,681		)
	Other expenses, net	(890		)		(1,091		)	(2,978		)	(3,254		)
	Net income	$	749			$	178		$	1,206		$	462

Dispositions_Tables

Dispositions (Tables)	9 Months Ended
	Sep. 30, 2014
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:
		Reporting	Disposition Date	Property Type	Square Feet
		Segment
	Owings Mills Business Park	Maryland	10/16/14	Business Park	180,475
	Corporate Campus at Ashburn Center	Northern Virginia	6/26/14	Business Park	194,184
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 two properties that are included in continuing operations for the periods presented (dollars in thousands):
		Three Months Ended							Nine Months Ended September 30,
		September 30,
		2014				2013			2014			2013
	Revenues	$	119			$	1,317		$	2,914		$	3,959
	Property operating expenses	(155		)		(364		)	(1,104		)	(1,137		)
	Depreciation and amortization	(209		)		(349		)	(977		)	(1,050		)
	Impairment of rental property	—				—			(3,956		)	—
	(Loss) income from operations of disposed property	(245		)		604			(3,123		)	1,772
	Gain on sale of rental property	—				—			21,230			—
	Net (loss) income from continuing operations	$	(245	)		$	604		$	18,107		$	1,772
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:
		Reporting	Disposition Date	Property Type	Square Feet
		Segment
	Patrick Center	Maryland	4/16/14	Office	66,269
	West Park	Maryland	4/2/14	Office	28,333
	Girard Business Center and Gateway Center	Maryland	1/29/14	Business Park and Office	341,973
	Worman’s Mill Court	Maryland	11/19/13	Office	40,099
	Triangle Business Center	Maryland	9/27/13	Business Park	74,429
	4200 Tech Court	Northern Virginia	8/15/13	Office	33,875
	Industrial Portfolio(1)	Various	May/June 2013	Industrial	4,280,985
	4212 Tech Court	Northern Virginia	6/5/13	Office	32,055
	(1)	During the second quarter of 2013, we sold 24 industrial properties, which consisted of two separate transactions. On May 7, 2013, we sold I-66 Commerce Center, a 236,000 square foot industrial property in Haymarket, Virginia. On June 18, 2013, we completed the sale of the remaining 23 industrial properties.
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							Nine Months Ended
		September 30,							September 30,
		2014				2013			2014			2013
	Revenues	$	—			$	1,907		$	867		$	22,081
	Net income (loss), before taxes(1)	—				107			(1,096		)	2,733
	Gain on sale of rental property	—				416			1,338			19,363
	(1)	During the first quarter of 2014, we accelerated $1.0 million of unamortized straight-line rent and deferred abatement costs related to the sale of Girard Business Center and Gateway Center.

Debt_Tables

Debt (Tables)	9 Months Ended
	Sep. 30, 2014
Debt Disclosure [Abstract]	'
Schedule of Borrowings	'
	Our borrowings consisted of the following (dollars in thousands):
		September 30,				December 31,
		2014				2013
	Mortgage loans, effective interest rates ranging from 4.40% to 6.63%, maturing at various dates through June 2023(1)	$	301,422			$	274,648
	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(1)	300,000				300,000
	Unsecured revolving credit facility, effective interest rate of LIBOR plus 1.50%, maturing October 2017(1)	213,000				99,000
		$	814,422			$	673,648
	(1)	At September 30, 2014, LIBOR was 0.16%. 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 September 30, 2014 and December 31, 2013 (dollars in thousands):
	Encumbered Property	Contractual		Effective			Maturity		September 30,			December 31,
		Interest Rate		Interest			Date		2014			2013
				Rate
	Annapolis Business Center(1)	5.74%		6.25	%		Jun-14		$	—		$	8,076
	Storey Park(2)(3)	LIBOR + 2.75%		5.8	%		Oct-14		22,000			22,000
	Jackson National Life Loan(4)	5.19%		5.19	%		Aug-15		65,242			66,116
	Hanover Business Center Building D	8.88%		6.63	%		Aug-15		142			252
	Chesterfield Business Center Buildings C, D, G and H	8.50%		6.63	%		Aug-15		399			681
	440 First Street, NW Construction Loan(2)	LIBOR + 2.50%		4.78	%		May-16		23,493			21,699
	Gateway Centre Manassas Building I	7.35%		5.88	%		November 2016		484			638
	Hillside I and II	5.75%		4.62	%		Dec-16		13,051			13,349
	Redland Corporate Center Buildings II & III	4.20%		4.64	%		Nov-17		66,127			67,038
	Hanover Business Center Building C	7.88%		6.63	%		Dec-17		543			653
	840 First Street, NE	5.72%		6.01	%		Jul-20		36,694			37,151
	Battlefield Corporate Center	4.26%		4.4	%		Nov-20		3,732			3,851
	Chesterfield Business Center Buildings A,B,E and F	7.45%		6.63	%		Jun-21		1,725			1,873
	Airpark Business Center	7.45%		6.63	%		Jun-21		941			1,022
	1211 Connecticut Avenue, NW	4.22%		4.47	%		Jul-22		29,833			30,249
	1401 K Street, NW	4.80%		4.93	%		Jun-23		37,016			—
				5.06	%	(5)			301,422			274,648
	Unamortized fair value adjustments								(500		)	(663		)
	Total contractual principal balance								$	300,922		$	273,985
	(1)	The loan was prepaid, without penalty, on May 1, 2014 with borrowings under our unsecured revolving credit facility.
	(2)	At September 30, 2014, LIBOR was 0.16%.
	(3)	The loan was repaid on October 16, 2014. Simultaneously with the repayment, our 97% owned consolidated joint venture entered into a new $22.0 million land loan with an applicable interest rate of LIBOR plus 2.50%, which matures on October 16, 2016, with a one-year extension at our option.
	(4)	At September 30, 2014, 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)	Weighted average interest rate on total mortgage debt.
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 September 30, 2014 (dollars in thousands):
		Maturity Date		Amount				Interest Rate(1)
	Tranche A	October 2018		$	100,000			LIBOR, plus 145 basis points
	Tranche B	October 2019		100,000				LIBOR, plus 160 basis points
	Tranche C	October 2020		100,000				LIBOR, plus 190 basis points
				$	300,000
	(1)	At September 30, 2014, LIBOR was 0.16%. The interest rate spread is subject to change based on our maximum total indebtedness ratio. Based on our maximum total indebtedness ratio at September 30, 2014, the applicable interest rate spreads on Tranche A, Tranche B and Tranche C of the unsecured term loan will increase by 20 basis points, 20 basis points and 15 basis points, respectively, in November 2014. For more information, see note 9(e) Debt – Financial Covenants.

Derivative_Instruments_Tables

Derivative Instruments (Tables)	9 Months Ended
	Sep. 30, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Summary of Interest Rate Swap Agreements	'
	At September 30, 2014, we fixed LIBOR at a weighted average interest rate of 1.5% on $300.0 million of our variable rate debt through eleven interest rate swap agreements that are summarized below (dollars in thousands):
	Effective Date	Maturity Date	Notional	Interest Rate	Fixed LIBOR
			Amount	Contractual	Interest Rate
				Component
	Jul-11	Jul-16	$35,000	LIBOR	1.75%
	Jul-11	Jul-16	25,000	LIBOR	1.76%
	Jul-11	Jul-17	30,000	LIBOR	2.09%
	Jul-11	Jul-17	30,000	LIBOR	2.09%
	Sep-11	Jul-18	30,000	LIBOR	1.66%
	Jan-12	Jul-18	25,000	LIBOR	1.39%
	Mar-12	Jul-17	25,000	LIBOR	1.13%
	Mar-12	Jul-17	12,500	LIBOR	1.13%
	Mar-12	Jul-18	12,500	LIBOR	1.38%
	Jun-12	Jul-17	50,000	LIBOR	0.96%
	Jun-12	Jul-18	25,000	LIBOR	1.14%
		Total/Weighted Average	$300,000		1.51%

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2014
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 September 30, 2014 and December 31, 2013 (dollars in thousands):
		Balance at		Level 1		Level 2		Level 3
		September 30, 2014
	Non-recurring Measurements:
	Impaired real estate assets	$	12,500	$	—	$	12,500	$	—
	Recurring Measurements:
	Derivative instrument-swap assets	451		—		451		—
	Derivative instrument-swap liabilities	3,371		—		3,371		—
		Balance at		Level 1		Level 2		Level 3
		December 31, 2013
	Non-recurring Measurements:
	Impaired real estate assets	$	2,909	$	—	$	2,909	$	—
	Recurring Measurements:
	Derivative instrument-swap assets	551		—		551		—
	Derivative instrument-swap liabilities	4,576		—		4,576		—
Fair Value of Debt Instruments	'
	The carrying value and estimated fair value of our financial assets and liabilities are as follows (dollars in thousands):
		September 30, 2014				December 31, 2013
		Carrying		Fair		Carrying		Fair
		Value		Value		Value		Value
	Financial Assets:
	Notes receivable(1)	$	63,719	$	63,767	$	54,696	$	56,812
	Financial Liabilities:
	Mortgage debt	$	301,422	$	289,647	$	274,648	$	262,873
	Unsecured term loan	300,000		300,000		300,000		300,000
	Unsecured revolving credit facility	213,000		213,000		99,000		99,000
	Total	$	814,422	$	802,647	$	673,648	$	661,873
	(1)	The principal amount of our notes receivable was $63.8 million and $54.9 million at September 30, 2014 and December 31, 2013, respectively. On January 10, 2014, we amended the 950 F Street, NW mezzanine loan and increased the outstanding balance to $34.0 million.

Equity_Tables

Equity (Tables)	9 Months Ended
	Sep. 30, 2014
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, 2013	$	738,510		$	781		$	739,291		$	33,221
	Net income	16,614			—			16,614			327
	Changes in ownership, net	2,018			161			2,179			390
	Distributions to owners	(35,691		)	—			(35,691		)	(1,183		)
	Other comprehensive income	1,059			—			1,059			47
	Balance at September 30, 2014	$	722,510		$	942		$	723,452		$	32,802
		First			Non-redeemable			Total Equity			Redeemable
		Potomac			noncontrolling						noncontrolling
		Realty Trust			interests						interests
	Balance at December 31, 2012	$	658,765		$	3,728		$	662,493		$	34,367
	Net income (loss)	14,526			(20		)	14,506			216
	Changes in ownership, net	107,836			249			108,085			273
	Distributions to owners	(33,428		)	—			(33,428		)	(1,168		)
	Other comprehensive income	5,767			—			5,767			284
	Balance at September 30, 2013	$	753,466		$	3,957		$	757,423		$	33,972
Company's Accumulated Other Comprehensive Loss	'
	A summary of our accumulated other comprehensive loss is as follows (dollars in thousands):
		2014			2013
	Beginning balance at January1,	$	(3,836	)	$	(10,917	)
	Net unrealized gain on derivative instruments	1,106			6,051
	Net gain attributable to noncontrolling interests	(47		)	(284		)
	Ending balance at September 30,	$	(2,777	)	$	(5,150	)

Segment_Information_Tables

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2014
Segment Reporting [Abstract]	'
Summary of Segment Information	'
	The results of operations of our four reporting segments for the three and nine months ended September 30, 2014 and 2013 are as follows (dollars in thousands):
		Three Months Ended September 30, 2014
		Washington, D.C.(1)			Maryland			Northern Virginia			Southern Virginia			Consolidated
	Number of buildings	6			42			49			38			135
	Square feet	815,093			2,179,366			3,020,975			2,852,212			8,867,646
	Total revenues	$	8,489		$	11,154		$	13,309		$	9,051		$	42,003
	Property operating expense	(2,496		)	(2,540		)	(3,121		)	(3,065		)	(11,222		)
	Real estate taxes and insurance	(1,278		)	(956		)	(1,228		)	(741		)	(4,203		)
	Total property operating income	$	4,715		$	7,658		$	8,960		$	5,245		$	26,578
	Depreciation and amortization expense													(16,000		)
	General and administrative													(4,955		)
	Acquisition costs													(1,488		)
	Other expenses													(4,086		)
	Net income													$	49
	Capital expenditures(2)	$	5,320		$	1,875		$	1,516		$	2,001		$	10,767
		Three Months Ended September 30, 2013
		Washington, D.C.(3)			Maryland			Northern Virginia			Southern Virginia			Consolidated
	Number of buildings	3			53			51			38			145
	Square feet	502,690			2,544,481			3,085,740			2,852,240			8,985,151
	Total revenues	$	6,963		$	10,207		$	13,231		$	8,848		$	39,249
	Property operating expense	(1,591		)	(2,775		)	(3,088		)	(2,977		)	(10,431		)
	Real estate taxes and insurance	(1,151		)	(837		)	(1,372		)	(702		)	(4,062		)
	Total property operating income	$	4,221		$	6,595		$	8,771		$	5,169		$	24,756
	Depreciation and amortization expense													(14,343		)
	General and administrative													(6,346		)
	Acquisition costs													(173		)
	Other expenses													(6,134		)
	Income from discontinued operations													523
	Net loss													$	(1,717	)
	Capital expenditures(2)	$	4,758		$	2,662		$	2,798		$	1,979		$	12,609
		Nine Months Ended September 30, 2014
		Washington, D.C.(1)			Maryland			Northern Virginia			Southern Virginia			Consolidated
	Total revenues	$	23,256		$	34,025		$	40,122		$	27,205		$	124,608
	Property operating expense	(6,889		)	(8,913		)	(10,203		)	(8,984		)	(34,989		)
	Real estate taxes and insurance	(3,579		)	(2,934		)	(4,217		)	(2,114		)	(12,844		)
	Total property operating income	$	12,788		$	22,178		$	25,702		$	16,107		$	76,775
	Depreciation and amortization expense													(46,714		)
	General and administrative													(15,370		)
	Acquisition costs													(2,667		)
	Impairment of rental property													(3,956		)
	Other income													8,631
	Income from discontinued operations													242
	Net income													$	16,941
	Total assets(4)(5)	$	501,536		$	375,399		$	437,909		$	228,655		$	1,628,737
	Capital expenditures(2)	$	16,702		$	6,966		$	3,876		$	6,173		$	34,410
		Nine Months Ended September 30, 2013
		Washington, D.C.(3)			Maryland			Northern Virginia			Southern Virginia			Consolidated
	Total revenues	$	21,730		$	30,828		$	38,589		$	26,092		$	117,239
	Property operating expense	(4,831		)	(7,873		)	(9,222		)	(8,248		)	(30,174		)
	Real estate taxes and insurance	(3,746		)	(2,473		)	(4,302		)	(2,028		)	(12,549		)
	Total property operating income	$	13,153		$	20,482		$	25,065		$	15,816		$	74,516
	Depreciation and amortization expense													(42,538		)
	General and administrative													(16,598		)
	Acquisition costs													(173		)
	Contingent consideration related to acquisition of property													(75		)
	Other expenses													(22,506		)
	Income from discontinued operations													22,096
	Net income													$	14,722
	Total assets(4)(5)	$	334,427		$	406,789		$	426,839		$	230,390		$	1,511,283
	Capital expenditures(2)	$	17,543		$	10,597		$	11,100		$	7,513		$	47,729
	(1)	Includes occupied space at 440 First Street, NW and excludes Storey Park, which was placed in development in the third quarter of 2013.
	(2)	Capital expenditures for corporate assets not allocated to any of our reportable segments totaled $55 and $412 for the three months ended September 30, 2014 and 2013, respectively, and $693 and $976 for the nine months ended September 30, 2014 and 2013, respectively.
	(3)	Excludes 440 First Street, NW, which has been in redevelopment since its acquisition in 2010.
(4)	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 7, Investment in Affiliates.
(5)	Corporate assets not allocated to any of our reportable segments totaled $85,238 and $112,838 at September 30, 2014 and 2013, respectively.

Description_of_Business_Additi

Description of Business - Additional Information (Detail)	3 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
	JointVenture	sqft
	Person
	Property
	sqft
	Executives
Real Estate Properties [Line Items]	'	'
Number of separate reporting segments of properties	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	8,867,646	8,985,151
Unconsolidated joint ventures	5	'
Square footage of land for additional development	1,400,000	'
Occupancy rate in the Company's consolidated properties	87.00%	'
Number of tenants representing the 85.8% occupancy rate	581	'
Square footage in development or redevelopment not included on occupancy calculation	300,000	'
Percent of Annualized Cash Rent	26.00%	'
Wholly-owned Properties [Member]	'	'
Real Estate Properties [Line Items]	'	'
Area of real estate property	8,900,000	'
Unconsolidated Properties [Member]	'	'
Real Estate Properties [Line Items]	'	'
Area of real estate property	900,000	'

Summary_of_Significant_Account3

Summary of Significant Accounting Policies - Estimated Useful Lives of Company's Assets, by Class (Detail)	9 Months Ended		3 Months Ended
	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014
		Buildings	Minimum [Member]	Minimum [Member]	Maximum [Member]	Maximum [Member]
			Building improvements	Furniture, fixtures and equipment	Building improvements	Furniture, fixtures and equipment
Property, Plant and Equipment [Line Items]	'	'	'	'	'	'
Useful life	'	'39 years	'5 years	'5 years	'20 years	'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	'	'	'	'	'

Summary_of_Significant_Account4

Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
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		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Numerator for basic and diluted earnings per common share:	'	'	'	'
Income (loss) from continuing operations	$49	($2,240)	$16,699	($7,374)
Income from discontinued operations	0	523	242	22,096
Net income (loss)	49	-1,717	16,941	14,722
Net Income (Loss) Attributable to Noncontrolling Interest	-131	-211	327	196
Less: Net loss (income) from continuing operations attributable to noncontrolling interests	'	233	-317	770
Less: Net income from discontinued operations attributable to noncontrolling interests	0	-22	-10	-966
Net income (loss) attributable to First Potomac Realty Trust	180	-1,506	16,614	14,526
Less: Dividends on preferred shares	-3,100	-3,100	-9,300	-9,300
Net (loss) income attributable to common shareholders	-2,920	-4,606	7,314	5,226
Less: Allocation to participating securities	-80	-103	-235	-309
Net (loss) income attributable to common shareholders	($3,000)	($4,709)	$7,079	$4,917
Denominator for basic and diluted earnings per common share:	'	'	'	'
Basic	58,167	57,969	58,137	54,014
Diluted	58,167	57,969	58,209	54,014
Basic and diluted earnings per common share:	'	'	'	'
Loss from continuing operations	($0.05)	($0.09)	$0.12	($0.30)
(Loss) income from discontinued operations	$0	$0.01	$0	$0.39
Net loss	($0.05)	($0.08)	$0.12	$0.09

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		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'	'
Anti-dilutive securities excluded from computation of earnings per share, Amount	13,892,000	14,093,000	13,982,000	13,596,000
Stock Option Awards [Member]	'	'	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'	'
Anti-dilutive securities excluded from computation of earnings per share, Amount	1,103,000	1,397,000	1,143,000	1,455,000
Non-vested Share Awards [Member]	'	'	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'	'
Anti-dilutive securities excluded from computation of earnings per share, Amount	433,000	513,000	401,000	528,000
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	12,356,000	12,183,000	12,438,000	11,613,000

Rental_Property_Summary_of_Ren

Rental Property - Summary of Rental Property (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Property, Plant and Equipment [Line Items]	'	'
Rental property, net	$1,342,280	$1,203,299
Rental Property [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Land and land improvements	332,466	294,753
Buildings and improvements	970,832	868,027
Construction in process	102,618	93,269
Tenant improvements	161,006	146,176
Furniture, fixtures and equipment	5,153	5,047
Rental property, gross	1,572,075	1,407,272
Less: accumulated depreciation	($229,795)	($203,973)

Rental_Property_Additional_Inf

Rental Property - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended
	Aug. 04, 2011	Sep. 30, 2014
	acre	sqft
Segment Reporting Information [Line Items]	'	'
Area of land available for development in additional building space	'	1,400,000
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	'	55,400,000
Anticipated completion of redevelopment	'	139,000
Redevelopment Efforts Yet To Be Placed In Service	'	101,000
Leases, Acquired-in-Place [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Projected incremental investment in development project	'	2,000,000
Buildings	'	'
Segment Reporting Information [Line Items]	'	'
Projected incremental investment in development project	'	36,000,000
Tenant Improvements	'	'
Segment Reporting Information [Line Items]	'	'
Projected incremental investment in development project	'	11,000,000
Washington D C Reporting Segment [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Area of land available for development in additional building space	'	700,000
Development of area for operations by joint venture	1.6	'
Lease expiration date	31-Aug-13	'
Projected incremental investment in development project	'	54,600,000
Original cost basis of the property	'	43,300,000
Washington D C Reporting Segment [Member] | Greyhound Property [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Percentage of interest in joint venture	97.00%	'
Washington D C Reporting Segment [Member] | Maximum [Member] | 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 [Member] | 440 First Street, NW [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Placed in-service redevelopment efforts	'	38,000
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	'	500,000
Area of land placed under development	'	167,000
Projected incremental investment in development project	'	5,400,000
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

Acquisitions_Fair_Value_of_Ass

Acquisitions - Fair Value of Assets and Liabilities (Details) (USD $)	Sep. 30, 2014
In Thousands, unless otherwise specified
Business Acquisition [Line Items]	'
Land	$15,835
Acquired tenant improvements	3,374
Building and improvements	63,957
In-place leases	3,873
Acquired leasing commissions	1,678
Legal leasing fees	80
Total assets acquired	90,217
Below-market leases assumed	-1,217
Net assets acquired	89,000
Above Market Leases [Member]	'
Business Acquisition [Line Items]	'
Above-market leases acquired	$1,420

Acquisitions_Pro_Forma_Financi

Acquisitions - Pro Forma Financial Information (Details) (USD $)	9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Business Combinations [Abstract]	'	'
Pro forma total revenues	$136,743	$133,411
Pro forma net income	$19,691	$9,914
Basic (in dollars per share)	$170	$10

Acquisitions_Additional_Inform

Acquisitions - Additional Information (Details) (USD $)	0 Months Ended	3 Months Ended		9 Months Ended
	Apr. 08, 2014	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 24, 2014	Apr. 08, 2014	Jun. 25, 2014
						11 DuPont Circle, NW [Domain]	1401 K Street, NW	1775 Wiehle Avenue [Domain]
						Washington D C Reporting Segment [Member]	Washington D C Reporting Segment [Member]	Northern Virginia
						sqft	sqft	sqft
Business Acquisition [Line Items]	'	'	'	'	'	'	'	'
Business combination, square footage	'	'	'	'	'	153,000	117,378	130,048
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Buildings	'	'	'	'	'	$89,000,000	$58,000,000	$41,000,000
Mortgage Debt Assumed	37,300,000	'	'	'	'	'	'	'
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	'	'	'	'5 years 7 months 0 days	'	'	'	'
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual	'	2,700,000	'	4,000,000	'	'	'	'
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual	'	400,000	'	1,100,000	'	'	'	'
Acquisition costs	'	$1,488,000	$173,000	$2,667,000	$173,000	'	'	'

Notes_Receivable_Summary_of_No

Notes Receivable - Summary of Notes Receivable (Detail) (USD $)	3 Months Ended	9 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2014	Dec. 31, 2013
Receivables with Imputed Interest [Line Items]	'	'	'
Face Amount	$63,767	$63,767	$54,896
Unamortized Origination Fees	-48	-48	-200
Balance	63,719	63,719	54,696
Notes Receivables Issued on December 2010 [Member]	'	'	'
Receivables with Imputed Interest [Line Items]	'	'	'
Face Amount	34,000	34,000	25,000
Unamortized Origination Fees	'	'	-130
Balance	34,000	34,000	24,870
Interest Rate	9.75%	'	12.50%
Property	'	'950B FB Street,B NW	'950B FB Street,B NW
Notes Receivables Issued on April 2011 [Member]	'	'	'
Receivables with Imputed Interest [Line Items]	'	'	'
Face Amount	29,767	29,767	29,896
Unamortized Origination Fees	-48	-48	-70
Balance	$29,719	$29,719	$29,826
Interest Rate	9.00%	'	9.00%
Property	'	'AmericabsB Square	'AmericabsB Square

Notes_Receivable_Additional_In

Notes Receivable - Additional Information (Detail) (USD $)

3 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

12 Months Ended

3 Months Ended

12 Months Ended

0 Months Ended

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2014

Dec. 31, 2013

Apr. 30, 2011

Sep. 30, 2014

Dec. 31, 2013

Dec. 31, 2010

Jan. 10, 2014

Jan. 10, 2014

Jan. 10, 2014

sqft

sqft

sqft

sqft

Notes Receivables Issued on April 2011 [Member]

Notes Receivables Issued on April 2011 [Member]

Notes Receivables Issued on April 2011 [Member]

Notes Receivables Issued on April 2011 [Member]

Notes Receivables Issued on December 2010 [Member]

Notes Receivables Issued on December 2010 [Member]

Notes Receivables Issued on December 2010 [Member]

Notes Receivables Issued on December 2010 [Member]

Notes Receivables Issued on December 2010 [Member]

Notes Receivables Issued on December 2010 [Member]

sqft

sqft

Maximum [Member]

Minimum [Member]

Receivables with Imputed Interest [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Mezzanine loan provided to owners

'

'

'

'

'

'

'

$30,000,000

'

'

$25,000,000

$34,000,000

'

'

Area of real estate property

8,867,646

8,985,151

8,867,646

8,985,151

'

'

'

461,000

'

'

287,000

'

'

'

Maturity date of loan

'

'

'

'

'

1-May-16

'

'

'

'

'

'

'

'

Fixed interest rate on loan

'

'

'

'

9.00%

'

9.00%

'

9.75%

12.50%

'

'

12.50%

9.75%

Maturity date of loan

'

'

'

'

'

'

'

'

'

'

1-Apr-17

'

'

'

Interest income

1,500,000

'

4,500,000

4,400,000

'

'

'

'

1,500,000

'

'

'

'

'

Income from amortization of origination fees

7,000

17,000

25,000

52,000

'

'

'

'

'

'

'

'

'

'

Write-off of unamortized origination fees

'

'

'

'

'

'

'

'

$100,000

'

'

'

'

'

Investment_in_Affiliates_Compo

Investment in Affiliates - Components of Investments in Affiliates (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]	'		'
Company Investment	$48,008		$49,150
Prosperity Metro Plaza [Member]	'		'
Schedule of Equity Method Investments [Line Items]	'		'
Reporting Segment	'NorthernB Virginia		'
Ownership Interest	51.00%		'
Company Investment	25,466		24,735
1750 H Street, NW [Member]	'		'
Schedule of Equity Method Investments [Line Items]	'		'
Reporting Segment	'Washington,B D.C.		'
Ownership Interest	50.00%		'
Company Investment	14,732		16,780
Aviation Business Park [Member]	'		'
Schedule of Equity Method Investments [Line Items]	'		'
Reporting Segment	'Maryland		'
Ownership Interest	50.00%		'
Company Investment	5,524		5,008
Rivers Park I and II [Member]	'		'
Schedule of Equity Method Investments [Line Items]	'		'
Reporting Segment	'Maryland		'
Ownership Interest	25.00%	[1]	'
Company Investment	$2,286	[1]	$2,627	[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 $)	Sep. 30, 2014		Dec. 31, 2013		Sep. 30, 2013		Dec. 31, 2012
In Thousands, unless otherwise specified
Assets:	'		'		'		'
Rental property, net	$1,342,280		$1,203,299		'		'
Cash and cash equivalents	11,993		8,740		16,971		9,374
Total assets	1,628,737	[1],[2]	1,502,460		1,511,283	[1],[2]	'
Liabilities:	'		'		'		'
Total liabilities	872,483		729,948		'		'
Net assets	89,000		'		'		'
Recourse mortgage debt	814,422		673,648		'		'
Unconsolidated Joint Ventures	'		'		'		'
Assets:	'		'		'		'
Rental property, net	194,075		194,240		'		'
Cash and cash equivalents	3,686		3,680		'		'
Other assets	17,529		15,585		'		'
Total assets	215,290		213,505		'		'
Liabilities:	'		'		'		'
Mortgage loans(1)(2)	108,456	[3],[4]	106,384	[3],[4]	'		'
Other liabilities	7,793		5,046		'		'
Total liabilities	116,249		111,430		'		'
Net assets	99,041		102,075		'		'
Unconsolidated Entities [Member]	'		'		'		'
Liabilities:	'		'		'		'
Recourse mortgage debt	$2,800		'		'		'
[1]	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 7, Investment in Affiliates.
[2]	Corporate assets not allocated to any of our reportable segments totaled $85,238 and $112,838 at September 30, 2014 and 2013, respectively.
[3]	Includes the unamortized fair value adjustments recorded at acquisition upon the assumption of mortgage loans.
[4]	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	9 Months Ended			3 Months Ended			3 Months Ended	0 Months Ended
In Millions, unless otherwise specified	Sep. 26, 2014	Sep. 30, 2014	Sep. 30, 2014	Jul. 10, 2014	Jul. 10, 2014	Sep. 30, 2014	Sep. 26, 2014	Mar. 26, 2014	Sep. 30, 2014	Sep. 26, 2017
	Rate	Rate	Rate	Rate	1750 H Street [Domain]	Rivers Park I and II [Member]	Rivers Park I and II [Member]	Rivers Park I and II [Member]	Washington D C Reporting Segment [Member]	Subsequent Event
						sqft	Rate	Rate	Maximum [Member]	Rivers Park I and II [Member]
									sqft
Schedule of Equity Method Investments [Line Items]	'	'	'	'	'	'	'	'	'	'
Ownership Percentage in Unconsolidated Joint Venture	'	'	'	50.00%	'	'	25.00%	'	'	'
Investment in Affiliates Joint Venture Repaid Mortgage	'	'	'	'	$27.90	'	'	'	'	'
Investment in Affiliates Variable Interest Entity Square Feet	'	'	'	'	'	308,000	'	'	113,000	'
Investment in Affiliates Joint Venture Financing	'	'	'	32	'	'	28	'	'	'
Investment in Affiliates Joint Venture mortgage interest rate	'	3.92%	3.92%	'	'	'	'	'	'	'
Investment in Affiliates Joint Venture Loan Maturity Date	'	1-Aug-24	'	'	'	'	'	'	'	26-Sep-17
Investment in Affiliates Joint Venture Loan Prepayment Date	'	1-Aug-21	'	'	'	'	'	'	'	'
Debt Instrument, Interest Rate, Increase (Decrease)	60.00%	'	'	'	'	'	'	'	'	'
Percentage Of Principal Loan Amount And Unpaid Accrued Interest Recourse	'	'	'	'	'	'	10.00%	25.00%	'	'
Fees from joint ventures	'	$0.20	$0.50	'	'	'	'	'	'	'

Investment_in_Affiliates_Resul

Investment in Affiliates - Results of Operations of Company's Unconsolidated Joint Ventures (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Schedule of Equity Method Investments [Line Items]	'	'	'	'
Total revenues	$42,003	$39,249	$124,608	$117,239
Total operating expenses	-37,868	-35,355	-116,540	-102,107
Operating income	4,135	3,894	8,068	15,132
Depreciation and amortization	-16,000	-14,343	-46,714	-42,538
Other expenses, net	-4,086	-6,134	'	-22,506
Net income	412	19	385	54
Unconsolidated Joint Ventures	'	'	'	'
Schedule of Equity Method Investments [Line Items]	'	'	'	'
Total revenues	5,713	6,035	17,245	18,046
Total operating expenses	-1,818	-1,879	-5,738	-5,649
Operating income	3,895	4,156	11,507	12,397
Depreciation and amortization	-2,256	-2,887	-7,323	-8,681
Other expenses, net	-890	-1,091	-2,978	-3,254
Net income	$749	$178	$1,206	$462

Dispositions_Additional_Inform

Dispositions - Additional Information (Detail) (USD $)

3 Months Ended

9 Months Ended

3 Months Ended

0 Months Ended

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Jun. 26, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Oct. 16, 2014

Oct. 16, 2014

Oct. 16, 2014

Oct. 16, 2014

sqft

sqft

sqft

sqft

MARYLAND

Corporate Campus at Ashburn Center [Member]

West Park

Patrick Center

Land

Buildings

Tenant Improvements

Subsequent Event [Member]

Subsequent Event [Member]

Subsequent Event [Member]

Subsequent Event [Member]

Northern Virginia Reporting Segment [Member]

sqft

sqft

Owings Mills Business Park [Domain]

Owings Mills Business Park [Domain]

Owings Mills Business Park [Domain]

sqft

MARYLAND

sqft

SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number Of Buildings

135

145

135

145

'

'

'

'

'

'

'

4

'

4

'

Area of real estate property

8,867,646

8,985,151

8,867,646

8,985,151

'

194,184

28,333

66,269

'

'

'

'

'

'

180,475

Impairment of rental property

$0

$0

$3,956,000

$0

$4,000,000

'

'

'

'

'

'

'

'

'

'

Increase (decrease) in assets held-for-sale

200,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Proceeds from sale of properties

'

'

'

'

'

'

'

'

'

'

'

'

12,400,000

'

'

Property, Plant, and equipment, gross

'

'

'

'

'

'

'

'

2,700,000

11,800,000

1,500,000

'

'

'

'

Accumulated depreciation

3,500,000

'

3,500,000

'

'

'

'

'

'

'

'

'

'

'

'

Other current assets

$300,000

'

$300,000

'

'

'

'

'

'

'

'

'

'

'

'

Dispositions_Dispositions_Disp

Dispositions Dispositions - Disposed or Held-for-Sale Properties within Continuing Operations (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]	'	'	'	'
Impairment of rental property	$0	$0	($3,956)	$0
Corporate Campus at Ashburn Center and Owings Mills Business Park [Member] | Continuing Operations [Member]	'	'	'	'
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]	'	'	'	'
Revenues	119	1,317	2,914	3,959
Property operating expenses	-155	-364	-1,104	-1,137
Depreciation and amortization	-209	-349	-977	-1,050
Impairment of rental property	0	0	-3,956	0
(Loss) income from operations of disposed property	-245	604	-3,123	1,772
Gain on sale of rental property	0	0	21,230	0
Net (loss) income from continuing operations	($245)	$604	$18,107	$1,772

Dispositions_Summary_of_Comple

Dispositions - Summary of Completed Property Dispositions (Detail)

0 Months Ended

3 Months Ended

3 Months Ended

Jun. 18, 2013

7-May-13

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Property

sqft

Property

sqft

I 66 Commerce [Domain]

Patrick Center

West Park

Girard Business Center and Gateway Center

Wormanbs Mill Court

Triangle Business Center

4200 Tech Court

Industrial Portfolio

4212 Tech Court

sqft

sqft

sqft

sqft

sqft

sqft

sqft

sqft

sqft

Schedule Of Discontinued Operations [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

Reporting Segment

'

'

'

'

'

'Maryland

'Maryland

'Maryland

'Maryland

'Maryland

'NorthernB Virginia

'Various

[1]

'Northern Virginia

Disposition Date

'

'

'

'

7-May-13

16-Apr-14

2-Apr-14

29-Jan-14

19-Nov-13

27-Sep-13

15-Aug-13

18-Jun-13

5-Jun-13

Disposition Date

'

'

'

'

'

'

'

'

'

'

'

'May/JuneB 2013

[1]

'

Property Type

'

'

'

'

'

'Office

'Office

'BusinessB ParkB andB Office

'Office

'Business Park

'Office

'Industrial

[1]

'Office

Square feet

'

'

8,985,151

8,867,646

'

66,269

28,333

341,973

40,099

74,429

33,875

4,280,985

[1]

32,055

Number of industrial properties company sold

'

'

24

'

'

'

'

'

'

'

'

'

'

Square footage of industrial properties held for sale

'

236,000

'

'

'

'

'

'

'

'

'

'

'

Sale of remaining industrial properties

23

'

'

'

'

'

'

'

'

'

'

'

'

[1]

During the second quarter of 2013, we sold 24 industrial properties, which consisted of two separate transactions. On MayB 7, 2013, we sold I-66 Commerce Center, a 236,000 square foot industrial property in Haymarket, Virginia. On JuneB 18, 2013, we completed the sale of the remaining 23 industrial properties.

Dispositions_Net_Loss_Income_f

Dispositions - Net (Loss) Income from Discontinued Operations (Detail) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]	'		'		'		'
Unamortized straight-line rent	$1,000,000		'		'		'
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	0		1,907,000		867,000		22,081,000
Net income (loss), before taxes(1)	0	[1]	107,000	[1]	-1,096,000	[1]	2,733,000	[1]
Gain on sale of rental property	$0		$416,000		$1,338,000		$19,363,000
[1]	During the first quarter of 2014, we accelerated $1.0 million of unamortized straight-line rent and deferred abatement costs related to the sale of Girard Business Center and Gateway Center.

Debt_Schedule_of_Borrowings_De

Debt - Schedule of Borrowings (Detail) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Debt Instrument [Line Items]	'		'
Mortgage loans, effective interest rates ranging from 4.40% to 6.63%, maturing at various dates through June 2023(1)	$301,422	[1]	$274,648	[1]
Unsecured revolving credit facility, effective interest rate of LIBOR plus 1.50%, maturing October 2017(1)	213,000	[1]	99,000	[1]
Total long term debt	814,422		673,648
Effective interest rate on the notes	5.06%	[2]	'
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 1.45% to LIBOR plus 1.90%, with staggered maturity dates ranging from October 2018 to October 2020(1)	$300,000	[1]	$300,000	[1]
Debt instrument basis spread on variable rate, minimum	1.45%		'
Debt instrument basis spread on variable rate, maximum	1.90%		'
Debt instrument maturity date	'October 2018 to October 2020		'
Mortgage Loans	'		'
Debt Instrument [Line Items]	'		'
Debt instrument, interest rate, effective percentage rate range, minimum	4.40%		'
Debt instrument, interest rate, effective percentage rate range, maximum	6.63%		'
Debt instrument maturity date	'July 2022		'
Unsecured revolving credit facility	'		'
Debt Instrument [Line Items]	'		'
Effective interest rate on the notes	1.50%		'
Debt instrument maturity date	'October 2017		'
[1]	At SeptemberB 30, 2014, LIBOR was 0.16%. All references to LIBOR in the condensed consolidated financial statements refer to one-month LIBOR.
[2]	Weighted average interest rate on total mortgage debt.

Debt_Summary_of_Companys_Mortg

Debt - Summary of Company's Mortgage Debt (Detail) (USD $)

0 Months Ended

9 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

0 Months Ended

0 Months Ended

In Thousands, unless otherwise specified

Jun. 05, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Oct. 16, 2016

Oct. 16, 2014

Oct. 16, 2014

Sep. 30, 2014

Aug. 04, 2011

Oct. 16, 2016

Oct. 16, 2014

Oct. 16, 2014

Mortgage Loans

Mortgage Loans

Annapolis Business Center

Annapolis Business Center

Storey Park

Storey Park

Jackson National Life Loan

Jackson National Life Loan

Hanover Business Center Building D

Hanover Business Center Building D

Chesterfield Business Center Buildings C,D,G and H

Chesterfield Business Center Buildings C,D,G and H

440 First Street, NW Construction Loan

440 First Street, NW Construction Loan

Gateway Centre Manassas Building I

Gateway Centre Manassas Building I

Hillside I and II

Hillside I and II

Redland Corporate Center Buildings II & III

Redland Corporate Center Buildings II & III

Hanover Business Center Building C

Hanover Business Center Building C

840 First Street, NE

840 First Street, NE

Battlefield Corporate Center

Battlefield Corporate Center

Chesterfield Business Center Buildings A,B,E and F

Chesterfield Business Center Buildings A,B,E and F

Airpark Business Center

Airpark Business Center

1211 Connecticut Avenue, NW

1211 Connecticut Avenue, NW

1401 K Street, NW

1401 K Street, NW

Subsequent Event

Subsequent Event

Subsequent Event

Greyhound Property [Member]

Greyhound Property [Member]

Greyhound Property [Member]

Greyhound Property [Member]

Greyhound Property [Member]

Rate

Subsequent Event

Subsequent Event

Subsequent Event

Debt Instrument [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Contractual Interest Rate

'

'

'

'

'

5.74%

[1]

'

2.75%

'

5.19%

[2]

'

8.88%

'

8.50%

'

2.50%

'

7.35%

'

5.75%

'

4.20%

'

7.88%

'

5.72%

'

4.26%

'

7.45%

'

7.45%

'

4.22%

'

4.80%

'

'

'

'

5.00%

'

'

'

2.50%

Contractual Interest Rate

'

'

'

'

'

'

'

'LIBORB +B 2.75%

[3],[4]

'

'

'

'

'

'

'

'LIBORB +B 2.50%

[3]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Effective Interest Rate

'

5.06%

[5]

'

'

'

6.25%

[1]

'

5.80%

[3],[4]

'

5.19%

[2]

'

6.63%

'

6.63%

'

4.78%

[3]

'

5.88%

'

4.62%

'

4.64%

'

6.63%

'

6.01%

'

4.40%

'

6.63%

'

6.63%

'

4.47%

'

4.93%

'

'

'

'

'

'

'

'

'

Maturity Date

'

'

'

'

'

'June 2014

[1]

'

'October 2014

[3],[4]

'

'August 2015

[2]

'

'August 2015

'

'August 2015

'

'May 2016

[3]

'

'NovemberB 2016

'

'December 2016

'

'November 2017

'

'December 2017

'

'July 2020

'

'November 2020

'

'June 2021

'

'June 2021

'

'July 2022

'

'June 1, 2023

'

'

'

'

'

'

'

'

'

Total Mortgage Debt

'

$301,422

[6]

$274,648

[6]

'

'

$0

[1]

$8,076

[1]

$22,000

[3],[4]

$22,000

[3],[4]

$65,242

[2]

$66,116

[2]

$142

$252

$399

$681

$23,493

[3]

$21,699

[3]

$484

$638

$13,051

$13,349

$66,127

$67,038

$543

$653

$36,694

$37,151

$3,732

$3,851

$1,725

$1,873

$941

$1,022

$29,833

$30,249

$37,016

$0

'

'

$22,000

'

'

'

'

'

Unamortized fair value adjustments

'

-500

-663

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Total contractual principal balance

'

$814,422

$673,648

$300,922

$273,985

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$6,000

Debt instrument variable rate basis

'

0.16%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

LIBOR plus interest rate

2.50%

150.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2.50%

'

Maturity date

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

16-Oct-16

16-Oct-14

'

'

'

16-Oct-16

'

'

Percentage Of Interest In Joint Venture Owned By Entity

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

97.00%

'

'

'

[1]

The loan was prepaid, without penalty, on May 1, 2014 with borrowings under our unsecured revolving credit facility.

[2]

At SeptemberB 30, 2014, 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.

[3]

At SeptemberB 30, 2014, LIBOR was 0.16%.

[4]

(3)B The loan was repaid on October 16, 2014. Simultaneously with the repayment, our 97% owned consolidated joint venture entered into a new $22.0 million land loan with an applicable interest rate of LIBOR plus 2.50%, which matures on October 16, 2016, with a one-year extension at our option

[5]

Weighted average interest rate on total mortgage debt.

[6]

At SeptemberB 30, 2014, LIBOR was 0.16%. All references to LIBOR in the condensed consolidated financial statements refer to one-month LIBOR.

Debt_Additional_Information_De

Debt - Additional Information (Detail) (USD $)

0 Months Ended

3 Months Ended

9 Months Ended

3 Months Ended

3 Months Ended

9 Months Ended

1 Months Ended

9 Months Ended

0 Months Ended

12 Months Ended

1 Months Ended

Jun. 05, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2014

Aug. 04, 2011

Jan. 31, 2014

Sep. 30, 2013

Sep. 30, 2014

Jun. 05, 2013

Oct. 16, 2016

Oct. 16, 2014

Oct. 16, 2016

Oct. 16, 2014

Oct. 17, 2017

Oct. 16, 2014

31-May-16

Rate

Rate

Unsecured term loan

Unsecured revolving credit facility

440 First Street, NW Construction Loan

Interest Rate Swap

Unused lines of credit

Unused lines of credit

Line of Credit [Member]

Greyhound Property [Member]

Greyhound Property [Member]

440 First Street, NW [Member]

440 First Street, NW [Member]

440 First Street, NW [Member]

440 First Street, NW [Member]

Subsequent Event [Member]

Subsequent Event [Member]

Subsequent Event [Member]

Subsequent Event [Member]

Subsequent Event [Member]

Subsequent Event [Member]

Subsequent Event [Member]

Interest_Rate_Swaps

Interest_Rate_Swaps

Tranches

Rate

Greyhound Property [Member]

Greyhound Property [Member]

Greyhound Property [Member]

Greyhound Property [Member]

440 First Street, NW [Member]

Debt Instrument [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage Of Interest In Joint Venture Owned By Entity

'

'

'

'

'

'

'

'

'

'

'

'

'

'

97.00%

'

'

'

'

'

'

'

'

'

'

'

Mortgage Loans on Real Estate

'

$37,300,000

'

$37,300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$22,000,000

'

Debt Instrument, Interest Rate, Stated Percentage

'

'

'

'

'

'

'

'

2.50%

'

'

'

'

5.00%

'

'

'

'

'

'

'

'

'

'

2.50%

'

Amount borrowed

'

'

21,700,000

'

'

'

'

'

'

'

'

'

'

'

'

1,800,000

'

'

'

'

'

'

'

'

'

'

Borrowing capacity of a construction loan

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

43,500,000

'

'

'

'

'

'

'

Basis spread over variable rate

2.50%

'

'

150.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2.50%

'

'

'

Maturity date

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

16-Oct-16

16-Oct-14

16-Oct-16

'

'

'

30-May-16

Maturity Period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'1 year

'

'

'

'

'

'

'1 year

'

'

Recourse mortgage debt

'

814,422,000

'

814,422,000

'

673,648,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

6,000,000

'

Percentage of outstanding principal

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

50.00%

'

'

'

'

'

'

'

'

Number of tranches

'

'

'

'

'

'

3

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Outstanding balance of three tranches

'

300,000,000

'

300,000,000

'

300,000,000

300,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Unsecured revolving credit facility

'

213,000,000

'

213,000,000

'

'

'

105,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Line of Credit Facility, Funding

'

'

'

'

'

'

'

89,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Increase in fund due to borrowings of revolving credit facility

'

'

'

'

'

'

'

16,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Proceed to pay loan

'

'

'

'

'

'

'

8,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Weighted average borrowings outstanding on unsecured revolving credit facility

'

'

'

'

154,900,000

'

'

'

'

'

125,900,000

50,400,000

112,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Line of Credit Facility, Interest Rate During Period

'

1.60%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Line of Credit Facility, Average Interest Rate at Prior Period End

'

'

2.60%

'

2.80%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Maximum outstanding borrowings

'

216,000,000

83,000,000

'

245,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Weighted average interest rate

'

1.70%

'

1.70%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Available capacity on the unsecured revolving credit facility

'

97,100,000

'

97,100,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Line of credit facility basis spread on variable rate basis

'

1.50%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Annual commitment fee

'

0.25%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Fixed effective interest rate

'

1.50%

'

1.50%

'

'

'

'

'

1.51%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Amount on variable rate debt

'

'

'

'

'

'

'

'

'

$300,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of interest rate swap agreements

'

11

'

11

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt_Unsecured_Term_Loan_Detai

Debt - Unsecured Term Loan (Detail) (USD $)	0 Months Ended	9 Months Ended		3 Months Ended
In Thousands, unless otherwise specified	Jun. 05, 2013	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014		Sep. 30, 2014		Sep. 30, 2014
				Tranche A		Tranche B		Tranche C
Debt Instrument [Line Items]	'	'	'	'		'		'
Maturity Date	'	'	'	'OctoberB 2018		'OctoberB 2019		'OctoberB 2020
Amount	'	$300,000	$300,000	$100,000		$100,000		$100,000
Interest Rate	'	'	'	'LIBOR,B plusB 145B basisB points	[1]	'LIBOR, plus 160 basis points	[1]	'LIBOR, plus 190 basis points	[1]
Basis spread over variable rate	2.50%	150.00%	'	1.45%		1.60%		1.90%
[1]	At SeptemberB 30, 2014, LIBOR was 0.16%. The interest rate spread is subject to change based on our maximum total indebtedness ratio. Based on our maximum total indebtedness ratio at September 30, 2014, the applicable interest rate spreads on Tranche A, Tranche B and Tranche C of the unsecured term loan will increase by 20 basis points, 20 basis points and 15 basis points, respectively, in November 2014. For more information, see note 9(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	Sep. 30, 2014
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]	'
Derivative, Effective Date	31-Jul-11
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]	'
Derivative, Effective Date	31-Jul-11
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]	'
Derivative, Effective Date	31-Jul-11
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]	'
Derivative, Effective Date	31-Jul-11
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]	'
Derivative, Effective Date	30-Sep-11
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]	'
Derivative, Effective Date	31-Jan-12
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]	'
Derivative, Effective Date	31-Mar-12
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]	'
Derivative, Effective Date	31-Mar-12
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]	'
Derivative, Effective Date	31-Mar-12
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]	'
Derivative, Effective Date	30-Jun-12
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]	'
Derivative, Effective Date	30-Jun-12
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 $)	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2013
	Interest_Rate_Swaps	Interest Rate Swap	Interest Rate Swap	Interest Rate Swap	Interest Rate Swap	Interest Rate Swap	Interest Rate Swap
			Interest Expense	Interest Expense	Interest Expense	Interest Expense Year To Date	Interest Expense Year To Date
Derivatives, Fair Value [Line Items]	'	'	'	'	'	'	'
Fixed effective interest rate	1.50%	1.51%	'	'	'	'	'
Amount on variable rate debt	'	$300,000,000	'	'	'	'	'
Number of interest rate swap agreements	11	'	'	'	'	'	'
Accumulated other comprehensive loss reclassified as an increase in interest expense	'	'	1,000,000	1,200,000	'	3,100,000	3,500,000
Estimated accumulated other comprehensive loss reclassified as an increase in interest expense over the following twelve months	'	'	'	'	$2,800,000	'	'

Fair_Value_Measurements_Fair_V

Fair Value Measurements - Fair Value of Assets and Liabilities (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Non-recurring Measurements	'	'
Non-recurring Measurements:	'	'
Impaired real estate assets	$12,500	$2,909
Recurring Measurements	'	'
Recurring Measurements:	'	'
Derivative instrument-swap assets	451	551
Derivative instrument-swap liabilities	3,371	4,576
Level 1 | Non-recurring Measurements	'	'
Non-recurring Measurements:	'	'
Impaired real estate assets	0	0
Level 1 | Recurring Measurements	'	'
Recurring Measurements:	'	'
Derivative instrument-swap assets	0	0
Derivative instrument-swap liabilities	0	0
Level 2 | Non-recurring Measurements	'	'
Non-recurring Measurements:	'	'
Impaired real estate assets	12,500	2,909
Level 2 | Recurring Measurements	'	'
Recurring Measurements:	'	'
Derivative instrument-swap assets	451	551
Derivative instrument-swap liabilities	3,371	4,576
Level 3 | Non-recurring Measurements	'	'
Non-recurring Measurements:	'	'
Impaired real estate assets	0	0
Level 3 | Recurring Measurements	'	'
Recurring Measurements:	'	'
Derivative instrument-swap assets	0	0
Derivative instrument-swap liabilities	$0	$0

Fair_Value_Measurements_Additi

Fair Value Measurements - Additional Information (Detail) (USD $)	3 Months Ended		3 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Oct. 16, 2014	Oct. 16, 2014
			Interest Rate Swap	Subsequent Event [Member]	Subsequent Event [Member]
			Rate		Owings Mills Business Park [Domain]
Derivatives, Fair Value [Line Items]	'	'	'	'	'
Number Of Buildings	135	145	'	4	4
Impairment Of Properties	$4	'	'	'	'
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 $)	Sep. 30, 2014		Jan. 10, 2014	Dec. 31, 2013
Financial Assets:	'		'	'
Carrying value of notes receivable	$63,719,000		'	$54,696,000
Fair value of notes receivable	63,800,000		'	54,900,000
Financial Liabilities:	'		'	'
Mezzanine loan increased	'		34,000,000	'
Carrying Value	'		'	'
Financial Assets:	'		'	'
Carrying value of notes receivable	63,719,000	[1]	'	54,696,000	[1]
Financial Liabilities:	'		'	'
Carrying value of the debt instruments	814,422,000		'	673,648,000
Carrying Value | Mortgage debt	'		'	'
Financial Liabilities:	'		'	'
Carrying value of the debt instruments	301,422,000		'	274,648,000
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	213,000,000		'	99,000,000
Fair Value	'		'	'
Financial Assets:	'		'	'
Fair value of notes receivable	63,767,000	[1]	'	56,812,000	[1]
Financial Liabilities:	'		'	'
Fair value of the debt instruments	802,647,000		'	661,873,000
Fair Value | Mortgage debt	'		'	'
Financial Liabilities:	'		'	'
Fair value of the debt instruments	289,647,000		'	262,873,000
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	$213,000,000		'	$99,000,000
[1]	The principal amount of our notes receivable was $63.8 million and $54.9 million at September 30, 2014 and DecemberB 31, 2013, respectively. On JanuaryB 10, 2014, we amended the 950 F Street, NW mezzanine loan and increased the outstanding balance to $34.0 million.

Equity_Additional_Information_

Equity - Additional Information (Detail) (USD $)	0 Months Ended
	Jan. 29, 2014	Jan. 29, 2014	Jan. 29, 2014	Oct. 21, 2014	Nov. 17, 2014	Nov. 06, 2014	Oct. 21, 2014	Nov. 17, 2014	Nov. 06, 2014	Oct. 21, 2014
		Series A Preferred Shares	Common Shares [Member]	Subsequent Event [Member]	Subsequent Event [Member]	Subsequent Event [Member]	Subsequent Event [Member]	Subsequent Event [Member]	Subsequent Event [Member]	Subsequent Event [Member]
					Series A Preferred Shares	Series A Preferred Shares	Series A Preferred Shares	Common Shares [Member]	Common Shares [Member]	Common Shares [Member]
Dividends Payable [Line Items]	'	'	'	'	'	'	'	'	'	'
Dividend declared date	'	'	22-Jul-14	'	'	'	'	'	'	21-Oct-14
Common share dividend per share declared	$0.15	'	'	$0.15	'	'	'	'	'	'
Common share dividend per share annualized	$0.60	'	'	$0.60	'	'	'	'	'	'
Dividend paid date	'	15-Aug-14	15-Aug-14	'	17-Nov-14	'	'	17-Nov-14	'	'
Dividend record date	'	6-Aug-14	6-Aug-14	'	'	6-Nov-14	'	'	6-Nov-14	'
Dividends declared on Series A Preferred Shares	'	$0.48	'	'	'	'	$0.48	'	'	'

Equity_Companys_Allocation_Bet

Equity - Company's Allocation Between Non-controlling Interests (Detail) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'
Beginning Balance	$739,291	$662,493
Net income (loss)	16,614	14,506
Changes in ownership, net	2,179	108,085
Distributions to owners	-35,691	-33,428
Other comprehensive income	1,059	5,767
Ending Balance	723,452	757,423
Increase (Decrease) in Temporary Equity [Roll Forward]	'	'
Beginning Balance, Redeemable noncontrolling interests	33,221	34,367
Net income (loss), Redeemable noncontrolling interests	327	216
Change in ownership, net, Redeemable noncontrolling interests	390	273
Distributions to owners, Redeemable noncontrolling interests	-1,183	-1,168
Other comprehensive income, Redeemable noncontrolling interests	47	284
Ending Balance, Redeemable noncontrolling interests	32,802	33,972
First Potomac Realty Trust	'	'
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'
Beginning Balance	738,510	658,765
Net income (loss)	16,614	14,526
Changes in ownership, net	2,018	107,836
Distributions to owners	-35,691	-33,428
Other comprehensive income	1,059	5,767
Ending Balance	722,510	753,466
Non-redeemable Noncontrolling Interests	'	'
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'
Beginning Balance	781	3,728
Net income (loss)	'	-20
Changes in ownership, net	161	249
Ending Balance	$942	$3,957

Equity_Companys_Accumulated_Ot

Equity - Company's Accumulated Other Comprehensive Loss (Detail) (USD $)	3 Months Ended	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2014	Mar. 31, 2013	Dec. 31, 2012
Statement of Partners' Capital [Abstract]	'	'	'	'
Beginning balance	'	($3,836)	($5,150)	($10,917)
Net unrealized gain on derivative instruments	6,051	1,106	'	'
Net gain attributable to noncontrolling interests	-284	-47	'	'
Ending balance	'	($2,777)	($5,150)	($10,917)

Noncontrolling_Interests_Addit

Noncontrolling Interests - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended	12 Months Ended		0 Months Ended	3 Months Ended		9 Months Ended		0 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014	Dec. 31, 2013	Mar. 31, 2013	Aug. 04, 2011	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Aug. 04, 2011	Aug. 04, 2011
	sqft					Washington D C Reporting Segment [Member]	Washington D C Reporting Segment [Member]	840 First Street, NE [Member]	840 First Street, NE [Member]	Greyhound Property [Member]	Greyhound Property [Member]
						acre	sqft			Washington D C Reporting Segment [Member]	Washington D C Reporting Segment [Member]
											Maximum [Member]
											sqft
Business Acquisition [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Cost to acquire all of the outstanding common Operating Partnership units not owned by the Company	$30,900,000	'	$30,900,000	'	'	'	'	'	'	'	'
Fair value adjustment, cost basis	3,700,000	3,300,000	3,700,000	3,300,000	'	'	'	'	'	'	'
Outstanding Operating Partnership units not owned by the Company	'	'	2,630,577	2,627,452	'	'	'	'	'	'	'
Operating Partnership units not owned by Company	4.30%	4.30%	'	'	'	'	'	'	'	'	'
Operating Partnership units issued for acquisition	'	'	'	'	'	'	'	3,125	3,125	'	'
Operating Partnership units fair valued	'	'	'	'	'	'	'	40,000	40,000	'	'
Common operating partnership units redeemed for cash	0	'	0	'	0	'	'	'	'	'	'
Percentage of interest in joint venture	'	'	'	'	'	'	'	'	'	97.00%	'
Development of area for operations by joint venture	'	'	'	'	'	1.6	'	'	'	'	'
Area of land available for development in additional building space	1,400,000	'	'	'	'	'	700,000	'	'	'	712,000
Projected incremental investment in development project	'	'	'	'	'	'	54,600,000	'	'	'	'
Original cost basis of the property	'	'	'	'	'	'	$43,300,000	'	'	'	'

Segment_Information_Additional

Segment Information - Additional Information (Detail)	3 Months Ended
	Sep. 30, 2014
	Integer
Segment Reporting [Abstract]	'
Number of reportable segments	4

Segment_Information_Summary_of

Segment Information - Summary of Segment Information (Detail) (USD $)	3 Months Ended				9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013		Dec. 31, 2013
	sqft		sqft		sqft		sqft
Segment Reporting Information [Line Items]	'		'		'		'		'
Number of buildings	135		145		135		145		'
Square feet	8,867,646		8,985,151		8,867,646		8,985,151		'
Total revenues	$42,003		$39,249		$124,608		$117,239		'
Property operating expense	-11,222		-10,431		-34,989		-30,174		'
Real estate taxes and insurance	-4,203		-4,062		-12,844		-12,549		'
Total property operating income	26,578		24,756		76,775		74,516		'
Depreciation and amortization expense	-16,000		-14,343		-46,714		-42,538		'
General and administrative	-4,955		-6,346		-15,370		-16,598		'
Acquisition costs	-1,488		-173		-2,667		-173		'
Contingent consideration related to acquisition of property	0		0		0		-75		'
Impairment of rental property	0		0		-3,956		0		'
Other Nonoperating Income (Expense)	'		'		8,631		'		'
Other expenses	-4,086		-6,134		'		-22,506		'
Income from discontinued operations	0		-523		-242		-22,096		'
Net income (loss)	49		-1,717		16,941		14,722		'
Total assets	1,628,737	[1],[2]	1,511,283	[1],[2]	1,628,737	[1],[2]	1,511,283	[1],[2]	1,502,460
Capital expenditure	10,767	[3]	12,609	[3]	34,410	[3]	47,729	[2]	'
Capital expenditures for corporate assets not allocated to any reportable segments	55		693		412		976		'
Corporate assets not allocated to any reportable segments	85,238		112,838		85,238		112,838		'
Washington, D.C.	'		'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'		'
Number of buildings	6	[4]	3	[5]	6	[4]	3	[5]	'
Square feet	815,093	[4]	502,690	[5]	815,093	[4]	502,690	[5]	'
Total revenues	8,489	[4]	6,963	[5]	23,256	[4]	21,730	[5]	'
Property operating expense	-2,496	[4]	-1,591	[5]	-6,889	[4]	-4,831	[5]	'
Real estate taxes and insurance	-1,278	[4]	-1,151	[5]	-3,579	[4]	-3,746	[5]	'
Total property operating income	4,715	[4]	4,221	[5]	12,788	[4]	13,153	[5]	'
Total assets	501,536	[1],[2],[4]	334,427	[1],[2],[5]	501,536	[1],[2],[4]	334,427	[1],[2],[5]	'
Capital expenditure	5,320	[3],[4]	4,758	[3],[5]	16,702	[3],[4]	17,543	[2],[5]	'
Maryland	'		'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'		'
Number of buildings	42		53		42		53		'
Square feet	2,179,366		2,544,481		2,179,366		2,544,481		'
Total revenues	11,154		10,207		34,025		30,828		'
Property operating expense	-2,540		-2,775		-8,913		-7,873		'
Real estate taxes and insurance	-956		-837		-2,934		-2,473		'
Total property operating income	7,658		6,595		22,178		20,482		'
Total assets	375,399	[1],[2]	406,789	[1],[2]	375,399	[1],[2]	406,789	[1],[2]	'
Capital expenditure	1,875	[3]	2,662	[3]	6,966	[3]	10,597	[2]	'
Northern Virginia	'		'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'		'
Number of buildings	49		51		49		51		'
Square feet	3,020,975		3,085,740		3,020,975		3,085,740		'
Total revenues	13,309		13,231		40,122		38,589		'
Property operating expense	-3,121		-3,088		-10,203		-9,222		'
Real estate taxes and insurance	-1,228		-1,372		-4,217		-4,302		'
Total property operating income	8,960		8,771		25,702		25,065		'
Total assets	437,909	[1],[2]	426,839	[1],[2]	437,909	[1],[2]	426,839	[1],[2]	'
Capital expenditure	'		2,798	[3]	3,876	[3]	11,100	[2]	'
Southern Virginia	'		'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'		'
Number of buildings	38		38		38		38		'
Square feet	2,852,212		2,852,240		2,852,212		2,852,240		'
Total revenues	9,051		8,848		27,205		26,092		'
Property operating expense	-3,065		-2,977		-8,984		-8,248		'
Real estate taxes and insurance	-741		-702		-2,114		-2,028		'
Total property operating income	5,245		5,169		16,107		15,816		'
Total assets	228,655	[1],[2]	230,390	[1],[2]	228,655	[1],[2]	230,390	[1],[2]	'
Capital expenditure	2,001	[3]	1,979	[3]	6,173	[3]	7,513	[2]	'
Northern Virginia	'		'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'		'
Capital expenditure	$1,516		'		'		'		'
[1]	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 7, Investment in Affiliates.
[2]	Corporate assets not allocated to any of our reportable segments totaled $85,238 and $112,838 at September 30, 2014 and 2013, respectively.
[3]	Capital expenditures for corporate assets not allocated to any of our reportable segments totaled $55 and $412 for the three months ended September 30, 2014 and 2013, respectively, and $693 and $976 for the nine months ended September 30, 2014 and 2013, respectively.
[4]	Includes occupied space at 440 First Street, NW and excludes Storey Park, which was placed in development in the third quarter of 2013.
[5]	Excludes 440 First Street, NW, which has been in redevelopment since its acquisition in 2010.