First Potomac Realty Trust (FPO) Inactive 10-K20 Feb 152014 FY Annual reportFinancial data

Company Profile

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
Document and Entity Information (USD $)	Dec. 31, 2014	Feb. 17, 2015	Jun. 30, 2014
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	FALSE
Document Period End Date	31-Dec-14
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Entity Registrant Name	FIRST POTOMAC REALTY TRUST
Entity Central Index Key	1254595
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		58,798,488
Entity Public Float			$756,133,139

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Assets:
Rental property, net	$1,288,873	$1,144,455
Assets held-for-sale	59,717	106,468
Cash and cash equivalents	13,323	8,740
Escrows and reserves	2,986	7,673
Accounts and other receivables, net of allowance for doubtful accounts of $1,207 and $1,181, respectively	10,587	12,384
Accrued straight-line rents, net of allowance for doubtful accounts of $104 and $92, respectively	34,226	29,531
Notes receivable, net	63,679	54,696
Investment in affiliates	47,482	49,150
Deferred costs, net	43,991	42,311
Prepaid expenses and other assets	7,712	8,261
Intangible assets, net	45,884	38,791
Total assets	1,618,460	1,502,460
Liabilities:
Mortgage loans	305,139	270,167
Unsecured term loan	300,000	300,000
Unsecured revolving credit facility	205,000	99,000
Liabilities held-for-sale	4,562	5,541
Accounts payable and other liabilities	41,113	41,296
Accrued interest	1,720	1,663
Rents received in advance	7,971	5,898
Tenant security deposits	5,891	4,861
Deferred market rent, net	2,827	1,522
Total liabilities	874,223	729,948
Noncontrolling interests in the Operating Partnership	33,332	33,221
Equity:
Preferred Shares
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	913,282	911,533
Noncontrolling interests in a consolidated partnership	898	781
Accumulated other comprehensive loss	-3,268	-3,836
Dividends in excess of accumulated earnings	-360,066	-329,246
Total equity	710,905	739,291
Total liabilities, noncontrolling interests and equity	1,618,460	1,502,460
Series A Preferred Shares [Member]
Equity:
Preferred Shares	$160,000	$160,000

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Paranthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Allowance for doubtful accounts, accounts receivable and other	$1,207	$1,181
Allowance for doubtful accounts, Accrued straight-line rents	$104	$92
Preferred stock, par value, per share	$0.00	$0.00
Preferred stock, shares authorized	50,000	50,000
Series A Preferred Shares, liquidation preference, per share	$25	$25
Series A Preferred Shares, shares issued	6,400	6,400
Series A Preferred Shares, shares outstanding	6,400	6,400
Common Stock, par value	$0.00	$0.00
Common Stock, shares authorized	150,000	150,000
Common Stock, shares issued	58,815	58,704
Common Stock, shares outstanding	58,815	58,704

Consolidated_Statements_of_Ope

Consolidated Statements of Operations (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues:
Rental	$128,226	$118,337	$114,032
Tenant reimbursements and other	33,426	30,478	28,930
Total revenues	161,652	148,815	142,962
Operating expenses:
Property operating	43,252	38,280	34,322
Real estate taxes and insurance	17,360	16,074	14,185
General and administrative	21,156	21,979	23,568
Acquisition costs	2,681	602	49
Depreciation and amortization	61,796	54,567	51,457
Impairment of rental property	3,956	0	2,444
Contingent consideration related to acquisition of property	0	-213	152
Total operating expenses	150,201	131,289	126,177
Operating income	11,451	17,526	16,785
Other expenses, net:
Interest expense	24,696	32,803	40,602
Interest and other income	-6,799	-6,373	-6,047
Equity in (earnings) losses of affiliates	-775	47	-40
Gain on sale of investment	0	0	-2,951
Loss on debt extinguishment / modification	0	1,810	13,687
Gain on sale of rental property	-21,230	0	0
Gain on sale of rental property	-4,108	28,287	45,251
Total other (income) expenses	15,559	-10,761	-28,466
Benefit from income taxes	0	0	4,142
Income (loss) from continuing operations	15,559	-10,761	-24,324
Discontinued operations:
Income from operations	146	6,793	15,782
Loss on debt extinguishment	0	-4,414	0
Gain on sale of rental property	1,338	19,363	161
Income from discontinued operations	1,484	21,742	15,943
Net income (loss)	17,043	10,981	-8,381
Less: Net (income) loss attributable to noncontrolling interests	-199	93	986
Net income (loss) attributable to First Potomac Realty Trust	16,844	11,074	-7,395
Less: Dividends on preferred shares	-12,400	-12,400	-11,964
Net income (loss) attributable to common shareholders	$4,444	($1,326)	($19,359)
Basic and diluted earnings per common share:
Income (loss) from continuing operations	$0.05	($0.41)	($0.70)
Income from discontinued operations	$0.02	$0.38	$0.30
Net income (loss)	$0.07	($0.03)	($0.40)
Weighted Average Number of Shares Outstanding, Basic	58,150	55,034	50,120
Weighted average common shares outstanding b diluted	58,220	55,034	50,120

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (Loss) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Net income (loss)	$17,043	$10,981	($8,381)
Unrealized gain on derivative instruments	1,289	7,423	295
Unrealized loss on derivative instruments	-696	0	-5,629
Total comprehensive income (loss)	17,636	18,404	-13,715
Net (income) loss attributable to noncontrolling interests	-199	93	986
Net (gain) loss from derivative instruments attributable to noncontrolling interests	-25	-342	266
Comprehensive income (loss) attributable to First Potomac Realty Trust	$17,412	$18,155	($12,463)

Consolidated_Statements_of_Equ

Consolidated Statements of Equity (USD $)	Total	Series A Preferred Shares	Common Shares [Member]	Additional Paid-in Capital [Member]	Noncontrolling Interests in Consolidated Partnerships [Member]	Accumulated Other Comprehensive Loss [Member]	Dividends in Excess of Accumulated Earnings [Member]
In Thousands	Total	Series A Preferred Shares	Common Shares [Member]	Additional Paid-in Capital [Member]		Accumulated Other Comprehensive Loss [Member]	Dividends in Excess of Accumulated Earnings [Member]
Beginning balance at Dec. 31, 2011	$676,491	$115,000	$50	$798,171	$4,245	($5,849)	($235,126)
Net income (loss)	-8,381						-8,381
Net unrealized gain (loss) on derivative instruments	-5,334					-5,334
Net (income) loss attributable to noncontrolling interests	1,252					266	986
Dividends paid to common shareholders	-40,730						-40,730
Dividends on preferred shares	-11,702						-11,702
Shares issued in exchange for common Operating Partnership units	-4,065		-1	-4,064
Restricted stock expense	2,961			2,961
Exercise of stock options	71			71
Stock option and employee stock purchase plan expense	611			611
Issuance of common stock, net of net settlements	-2,114			-2,114
Issuance of preferred stock	-43,518	-45,000		-1,482
Adjustment of common Operating Partnership units to fair value	-1,926			-1,926
Noncontrolling interest in consolidated joint ventures, at acquisition	-582				-582
Income (loss) attributable to noncontrolling interest in consolidated joint ventures	65				65
Ending balance at Dec. 31, 2012	662,493	160,000	51	804,584	3,728	-10,917	-294,953
Net income (loss)	10,981						10,981
Net unrealized gain (loss) on derivative instruments	7,423					7,423
Net (income) loss attributable to noncontrolling interests	-249					-342	93
Dividends paid to common shareholders	-32,917						-32,917
Dividends on preferred shares	-12,400						-12,400
Shares issued in exchange for common Operating Partnership units	-50						-50
Restricted stock expense	3,863			3,863
Exercise of stock options	163			163
Stock option and employee stock purchase plan expense	549			549
Issuance of common stock, net of net settlements	-103,589		-8	-103,581
Acquisition Of Remaining Interests In Consolidated Joint Venture	-4,565			-1,387	-3,178
Adjustment of common Operating Partnership units to fair value	180			180
Net distributions from / contributions to noncontrolling interest in consolidated joint ventures	250				250
Income (loss) attributable to noncontrolling interest in consolidated joint ventures	-19				-19
Ending balance at Dec. 31, 2013	739,291	160,000	59	911,533	781	-3,836	-329,246
Net income (loss)	17,043						17,043
Net unrealized gain (loss) on derivative instruments	593					593
Net (income) loss attributable to noncontrolling interests	-224					-25	-199
Dividends paid to common shareholders	-35,198						-35,198
Dividends on preferred shares	-12,400						-12,400
Accrued common dividends	-66						-66
Restricted stock expense	2,860			2,860
Exercise of stock options	174			174
Stock option and employee stock purchase plan expense	536			536
Issuance of common stock, net of net settlements	-397			-397
Adjustment of common Operating Partnership units to fair value	-1,424			-1,424
Net distributions from / contributions to noncontrolling interest in consolidated joint ventures	117				117
Ending balance at Dec. 31, 2014	$710,905	$160,000	$59	$913,282	$898	($3,268)	($360,066)

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flow from operating activities:
Net income (loss)	$17,043	$10,981	($8,381)
Discontinued operations:
Gain on sale of rental property	-1,338	-19,363	-161
Loss on debt extinguishment / modification	0	192	0
Depreciation and amortization	3,665	8,937	14,958
Impairment of rental property	0	4,092	1,072
Depreciation and amortization	62,843	55,581	52,855
Stock based compensation	3,731	4,412	3,572
Bad debt expense	1,110	800	702
Deferred income taxes	0	0	-3,533
Amortization of deferred market rent	-14	76	195
Amortization of financing costs and discounts	1,445	2,851	2,397
Equity in (earnings) losses of affiliates	-775	47	-40
Distributions from investments in affiliates	1,356	2,064	1,796
Contingent consideration related to acquisition of property	0	-213	152
Contingent consideration payments in excess of fair value at acquisition date	0	-987	0
Impairment of rental property	3,956	0	2,444
Gain on sale of rental property	-21,230	0	0
Gain on sale of investment	0	0	-2,951
Loss on debt extinguishment / modification	0	223	2,379
Changes in assets and liabilities:
Escrows and reserves	4,693	6,256	5,889
Accounts and other receivables	1,475	1,763	-4,152
Accrued straight-line rents	-7,968	-8,078	-10,343
Prepaid expenses and other assets	326	1,074	-348
Tenant security deposits	677	1,022	289
Accounts payable and accrued expenses	1,227	-2,340	3,444
Accrued interest	56	-990	-129
Rents received in advance	1,984	-3,616	-1,603
Deferred costs	-11,309	-9,492	-12,664
Total adjustments	45,910	44,311	56,220
Net cash provided by operating activities	62,953	55,292	47,839
Cash flows from investing activities:
Investment in note receivable	-9,000	0	0
Principal payments from note receivable	176	104	0
Proceeds from sale of rental property	97,701	263,469	14,341
Proceeds from sale of investment	0	0	25,705
Change in escrow and reserve accounts	0	-10	-61
Additions to rental property and furniture, fixtures and equipment	-39,338	-48,125	-58,371
Additions to construction in progress	-11,451	-19,877	-12,115
Acquisition of rental property and associated intangible assets	-150,731	-30,000	0
Acquisition of noncontrolling interest in consolidated joint venture	0	-4,565	0
Investment in affiliates	-1,988	-665	-2,512
Distributions from investments in affiliates	3,075	0	0
Net cash (used in) provided by investing activities	-111,556	160,331	-33,013
Cash flows from financing activities:
Financing costs	-870	-5,568	-3,932
Issuance of debt	250,518	152,199	445,400
Issuance of common shares, net	0	105,085	3,599
Issuance of preferred shares, net	0	0	43,518
Payment of deferred acquisition costs and contingent consideration	0	-9,036	0
Contributions from consolidated joint venture partners	213	250	0
Distributions to consolidated joint venture partners	-96	0	-592
Repayments of debt	-147,577	-412,381	-456,109
Dividends to common shareholders	-35,198	-32,917	-40,730
Dividends to preferred shareholders	-12,400	-12,400	-11,267
Distributions to noncontrolling interests	-1,578	-1,557	-2,159
Operating partnership unit redemptions	0	-95	0
Proceeds from stock option exercises	174	163	71
Net cash provided by (used in) financing activities	53,186	-216,257	-22,201
Net increase (decrease) in cash and cash equivalents	4,583	-634	-7,375
Cash and cash equivalents, beginning of year	8,740	9,374	16,749
Cash and cash equivalents, end of year	13,323	8,740	9,374
Cash paid for interest, net	23,083	32,116	40,769
Cash paid for income based franchise taxes	0	0	714
Non-cash investing and financing activities:
Debt assumed in connection with the acquisition of rental property	37,269	0	0
Settlements of common shares	487	1,348	1,252
Change in fair value of the outstanding common Operating Partnership units	1,424	-215	2,074
Conversion of common Operating Partnership units for common shares	0	0	4,064
Issuance of common Operating Partnership units in connection with the acquisition of rental property	40	418	0
Change in accruals:
Additions to rental property and furniture, fixtures and equipment	653	-4,959	1,988
Additions to development and redevelopment	($275)	($3,118)	$3,705

Consolidated_Statements_of_Cas1

Consolidated Statements of Cash Flows (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Capitalized interest on indebtedness paid in cash	$3,200,000	$2,500,000	2,400,000
1401 K Purchase Price	188,000,000
Mortgage Loans on Real Estate	37,300,000
Surrendered common shares to satisfy statutory minimum federal income tax obligations	500,000	1,300,000	1,300,000
Change in redemption value, noncontrolling interest	4,700,000	3,300,000
Development and Redevelopment [Member]
Number of operating partnership units redeemed		0	322,302
Accrued capital expenditure	1,300,000	1,500,000	4,600,000
Furniture and Fixtures [Member]
Accrued capital expenditure	9,300,000	8,500,000	13,200,000
Eight Four Zero First Street Ne [Member]
Partners' Capital Account, Units, Acquisitions	3,125	35,911	0
Operating Partnership Units Fair Valued	$40,000	$400,000

Description_of_Business

Description of Business	12 Months Ended
Description of Business	Dec. 31, 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 strategically focuses on acquiring and redeveloping properties that it believes can benefit from its intensive property management, leasing expertise, market knowledge and established relationships, and seeks to reposition these properties to increase their profitability and value. The Company’s portfolio primarily contains a mix of single-tenant and multi-tenant office properties and business parks. Office properties are single-story and multi-story buildings that are primarily for office use; and business parks contain buildings with office features combined with some industrial property space. The Company separates its properties into four distinct reporting segments, which it refers to as the Washington, D.C., Maryland, Northern Virginia and Southern Virginia reporting segments.

	References in these 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 December 31, 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 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 December 31, 2014, we wholly owned or had a controlling interest in properties totaling 8.8 million square feet and had a noncontrolling ownership interest in properties totaling an additional 0.9 million square feet through five unconsolidated joint ventures. We also owned land that can support 1.4 million square feet of additional development. Our consolidated properties were 87.9% occupied by 582 tenants at December 31, 2014. We did not include square footage that was in development or redevelopment, which totaled 0.2 million square feet at December 31, 2014, in our occupancy calculation. We derive substantially all of our revenue from leases of space within our properties. As of December 31, 2014, our largest tenant was the U.S. Government, which accounted for 14% of our total annualized cash basis rent, and the U.S. Government combined with government contractors, accounted for 26% of our total annualized cash basis rent as of December 31, 2014. We operate so as to qualify as a real estate investment trust (“REIT”) for federal income tax purposes.

	For the year ended December 31, 2014, we had consolidated total revenues of $161.7 million and consolidated total assets of $1.6 billion. Financial information related to our four reporting segments is set forth in note 18, Segment Information, to our consolidated financial statements.

Summary_of_Significant_Account

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2014

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

(a) Principles of Consolidation

Our consolidated financial statements include our accounts and the accounts of our Operating Partnership and the subsidiaries in which we or our Operating Partnership has a controlling interest, which includes First Potomac Management LLC, a wholly owned subsidiary that manages the majority of our properties. All intercompany balances and transactions have been eliminated in consolidation.

(b) Use of Estimates

The preparation of consolidated financial statements in conformity with U.S. generally accepted accounting principles (“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 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.

We generate substantially all of our revenue from leases on our properties. We recognize rental revenue on a straight-line basis over the term of our leases, which includes fixed-rate renewal periods leased at below market rates at acquisition or inception. Accrued straight-line rents represent the difference between rental revenue recognized on a straight-line basis over the term of the respective lease agreements and the rental payments contractually due for leases that contain abatement or fixed periodic increases. We consider current information, credit quality, historical trends, economic conditions and other events regarding the tenants’ ability to pay their obligations in determining if amounts due from tenants, including accrued straight-line rents, are ultimately collectible. The uncollectible portion of the amounts due from tenants, including accrued straight-line rents, is charged to Property operating expense in our consolidated statements of operations in the period in which the determination is made and to allowance for doubtful accounts in either Accounts and other receivables or Accrued straight-line rents on our consolidated balance sheets. During 2014, 2013 and 2012, we incurred charges of $1.1 million, $0.8 million and $0.7 million, respectively, related to anticipated uncollectible amounts from tenants, including accrued straight-line rents. We consider similar criteria in assessing impairment associated with outstanding loans or notes receivable and whether any allowance for anticipated credit loss is appropriate.

Tenant leases generally contain provisions under which the tenants reimburse us for a portion of property operating expenses and real estate taxes incurred by us. Such reimbursements are recognized in the period in which the expenses are incurred. We record a provision for losses on estimated uncollectible accounts receivable based on our analysis of risk of loss on specific accounts. Lease termination fees are recognized on the date of termination when the related lease or portion thereof is cancelled, the collectability of the fee is reasonably assured and we have possession of the terminated space. We recognized lease termination fees included in “Tenant reimbursements and other revenues” in our consolidated statements of operations of $1.1 million, $1.0 million and $2.0 million for the years ended December 31, 2014, 2013 and 2012, respectively.

(d) Cash and Cash Equivalents

We consider all highly liquid investments with a maturity of 90 days or less at the date of purchase to be cash equivalents.

(e) Escrows and Reserves

Escrows and reserves represent cash restricted for debt service, real estate taxes, insurance, leasing commissions and tenant improvements. We reflect cash inflows and outflows from our escrows and reserves accounts related to debt service, real estate taxes, insurance and leasing commissions within net cash provided by operating activities and our cash inflows and outflows related tenant improvements within net cash used by investing activities on our consolidated statements of cash flows.

(f) Deferred Costs

Financing costs related to long-term debt are deferred and amortized over the remaining life of the debt using the effective interest method. Leasing costs related to the execution of tenant leases and lease incentives are deferred and amortized ratably over the term of the related leases. Accumulated amortization of these combined costs was $24.8 million and $20.7 million at December 31, 2014 and 2013, respectively.

The following table sets forth scheduled future amortization for deferred financing and leasing costs at December 31, 2014 (amounts in thousands):

Deferred

Financing(1)

Leasing(1)(2)

Lease Incentive

2015

1,905

5,446

637

2016

1,533

4,977

637

2017

1,153

4,181

552

2018

836

3,593

518

2019

308

2,828

443

Thereafter

425

7,849

1,627

6,160

28,874

4,414

(1)

Includes amounts from properties that were classified as held-for-sale at December 31, 2014.

(2)

Excludes the amortization of $5.6 million of leasing costs that have yet to be placed in-service as the associated tenants have not moved into their related spaces and, therefore, the period over which the leasing costs will be amortized has yet to be determined.

(g) 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

Tenant improvements

Shorter of the useful life of the asset or the term of the related lease

We regularly review market conditions for possible impairment of a property’s carrying value. When circumstances such as adverse market conditions, changes in management’s intended holding period or potential sale to a third party indicate a possible impairment of the carrying value of a property, an impairment analysis is performed. We assess potential impairments based on an estimate of the future undiscounted cash flows (excluding interest charges) expected to result from the property’s use and eventual disposition. This estimate is based on projections of future revenues, expenses, capital improvement costs to maintain the operating capacity, expected holding periods and capitalization rates. These cash flows consider factors such as expected market trends and leasing prospects, as well as the effects of leasing demand, competition and other factors. If impairment exists due to the inability to recover the carrying value of a real estate investment based on forecasted undiscounted cash flows, an impairment loss is recorded to the extent that the carrying value exceeds the estimated fair value of the property. Further, we will record an impairment loss if we expect to dispose of a property, in the near term, at a price below carrying value. In such an event, we will record an impairment loss based on the difference between a property’s carrying value and its projected sales price less any estimated costs to sell.

We will classify a building as held-for-sale in accordance with GAAP in the period in which we have made the decision to dispose of the building, our Board of Trustees or a designated delegate has approved the sale, there is a high likelihood a binding agreement to purchase the property will be signed under which the buyer will be required to commit a significant amount of nonrefundable cash and no significant financing contingencies exist that could cause the transaction not to be completed in a timely manner. We will cease recording depreciation on a building once it has been classified as held-for-sale. In the second quarter of 2014, we prospectively adopted 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(q), 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 liabilities related to the building as held-for-sale in our consolidated balance sheets for the periods presented. Interest expense is reclassified to discontinued operations only to the extent the disposed or held-for-sale property is secured by specific mortgage debt and the mortgage debt will not be assigned to another property owned by us after the disposition.

We recognize the fair value, if sufficient information exists to reasonably estimate the fair value, of any liability for conditional asset retirement obligations when assumed or incurred, which is generally upon acquisition, construction, development or redevelopment and/or through the normal operation of the asset.

We capitalize interest costs incurred on qualifying expenditures for real estate assets under development or redevelopment, which include our investments in assets owned through unconsolidated joint ventures that are under development or redevelopment, while being readied for their intended use in accordance with accounting requirements regarding capitalization of interest. We will capitalize interest when qualifying expenditures for the asset have been made, activities necessary to get the asset ready for its intended use are in progress and interest costs are being incurred. Capitalized interest also includes interest associated with expenditures incurred to acquire developable land while development activities are in progress. We also capitalize direct compensation costs of our construction personnel who manage the development and redevelopment projects, but only to the extent the employee’s time can be allocated to a project. Any portion of construction management costs not directly attributable to a specific project are recognized as general and administrative expense in the period incurred. We do not capitalize any other general and administrative costs such as office supplies, office rent expense or an overhead allocation to our development or redevelopment projects. Capitalized compensation costs were immaterial during 2014, 2013 and 2012. 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.

(h) Purchase Accounting

Acquisitions of rental property, including any associated intangible assets, are measured at fair value at the date of acquisition. Any liabilities assumed or incurred are recorded at their fair value at the time of acquisition. The fair value of the acquired property is allocated between land and building (on an as-if vacant basis) based on management’s estimate of the fair value of those components for each type of property and to tenant improvements based on the depreciated replacement cost of the tenant improvements, which approximates their fair value. The fair value of the in-place leases is recorded as follows:

•

the fair value of leases in-place on the date of acquisition is based on absorption costs for the estimated lease-up period in which vacancy and foregone revenue are avoided due to the presence of the acquired leases;

•

the fair value of above and below-market in-place leases based on the present value (using a discount rate that reflects the risks associated with the acquired leases) of the difference between the contractual rent amounts to be paid under the assumed lease and the estimated market lease rates for the corresponding spaces over the remaining non-cancelable terms of the related leases, which range from one to fourteen years; and

•

the fair value of intangible tenant or customer relationships.

Our determination of these fair values requires us to estimate market rents for each of the leases and make certain other assumptions. These estimates and assumptions affect the rental revenue, and depreciation and amortization expense recognized for these leases and associated intangible assets and liabilities.

(i) Investment in Affiliates

We may continue to grow our portfolio by entering into ownership arrangements with third parties for which we do not have a controlling interest. The structure of the arrangement may affect our accounting treatment as the entities may qualify as variable interest entities (“VIE”) based on disproportionate voting to equity interests, or other factors. In determining whether to consolidate an entity, we assess the structure and intent of the entity relationship as well its power to direct major decisions regarding the entity’s operations. When our investment in an entity meets the requirements for the equity method of accounting, we will record our initial investment in our consolidated balance sheets as “Investment in affiliates.” The initial investment in the entity is adjusted to recognize our share of earnings, losses, distributions received from the entity or additional contributions. Basis differences, if any, are recognized over the life of the venture as an adjustment to “Equity in (earnings) losses of affiliates” in our consolidated statements of operations. Our respective share of all earnings or losses from the entity will be recorded in our consolidated statements of operations as “Equity in (earnings) losses of affiliates.”

When we are deemed to have a controlling interest in a partially-owned entity, we will consolidate all of the entity’s assets, liabilities, operating results and cash flows within our consolidated financial statements. The cash contributed to the consolidated entity by the third party, if any, will be reflected in the permanent equity section of our consolidated balance sheets to the extent the associated ownership interests 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 for any distributions received or additional contributions made by the third party. The earnings or losses from the entity attributable to the third party will be recorded in our consolidated statements of operations as a component of “Net loss attributable to noncontrolling interests.”

(j) Sales of Rental Property

We account for sales of rental property in accordance with the requirements for full profit recognition, which occurs when the sale is consummated, the buyer has made adequate initial and continuing investments in the property, our receivable is not subject to future subordination, and we do not have substantial continuing involvement with the property. Once the requirements for full profit recognition are achieved, the related assets and liabilities are removed from the balance sheet and the resultant gain or loss is recorded in the period the sale is consummated. For sales transactions that do not meet the criteria for full profit recognition, we account for the transactions as partial sales or financing arrangements required by GAAP. For sales transactions with continuing involvement after the sale, if the continuing involvement with the property is limited by the terms of the sales contract, profit is recognized at the time of sale and is reduced by the maximum exposure to loss related to the nature of the continuing involvement. Sales to entities in which we have or receive an interest are accounted for as partial sales.

For sales transactions that do not meet sale criteria, we evaluate the nature of the continuing involvement, including put and call provisions, if present, and accounts for the transaction as a financing arrangement, profit-sharing arrangement, leasing arrangement or other alternate method of accounting rather than as a sale, based on the nature and extent of the continuing involvement. Some transactions may have numerous forms of continuing involvement. In those cases, we determine which method is most appropriate based on the substance of the transaction.

(k) Intangible Assets

Intangible assets include the fair value of acquired tenant or customer relationships and the fair value of in-place leases at acquisition. Customer relationship fair values are determined based on our evaluation of the specific characteristics of each tenant’s lease and our overall relationship with the tenant. Characteristics we consider include the nature and extent of our existing business relationships with the tenant, growth prospects for developing new business with the tenant, the tenant’s credit quality and expectations of lease renewals. The fair value of customer relationship intangible assets is amortized to expense over the lesser of the initial lease term and any expected renewal periods or the remaining useful life of the building. We determine the fair value of the in-place leases at acquisition by estimating the leasing commissions avoided by having in-place tenants and the operating income that would have not been recognized during the estimated time required to lease the space occupied by existing tenants at the acquisition date. The fair value attributable to existing tenants is amortized to expense over the initial term of the respective leases. Should a tenant terminate its lease, the unamortized portion of the in-place lease fair value is charged to expense by the date of termination.

Deferred market rent liability consists of the acquired leases with below-market rents at the date of acquisition. The fair value attributed to deferred market rent assets, which consist of above-market rents at the date of acquisition, is recorded as a component of deferred costs. Above and below-market lease fair values are determined on a lease-by-lease basis based on the present value (using a discounted rate that reflects the risks associated with the acquired leases) of the difference between the contractual rent amounts to be paid under the lease and the estimated market lease rates for the corresponding spaces over the remaining non-cancelable terms of the related leases including any below-market fixed rate renewal periods. The capitalized below-market lease fair values are amortized as an increase to rental revenue over the initial term and any below-market fixed-rate renewal periods of the related leases. Capitalized above-market lease fair values are amortized as a decrease to rental revenue over the initial term of the related leases.

In conjunction with our initial public offering and related formation transactions, First Potomac Management, Inc. contributed all of the capital interests in First Potomac Management LLC. The $2.1 million fair value of the in-place workforce acquired has been classified as goodwill and is included as a component of "Intangible assets, net" on the consolidated balance sheets. In 2011, we recognized additional goodwill of $4.8 million representing the residual difference between the consideration transferred for the purchase of 840 First Street, NE, which was acquired in March 2011, and the acquisition date fair value of the identifiable assets acquired and liabilities assumed and deferred taxes representing the difference between the fair value of acquired assets at acquisition and the carryover basis used for income tax purposes. In accordance with accounting requirements regarding goodwill and other intangibles, all acquired goodwill that relates to the operations of a reporting unit and is used in determining the fair value of a reporting unit is allocated to our appropriate reporting unit in a reasonable and consistent manner.

We assess goodwill for impairment annually at the end of our fiscal year and in interim periods if certain events occur indicating the carrying value may be impaired. We perform our analysis for potential impairment of goodwill in accordance with GAAP and are permitted to make a qualitative assessment of whether it is more likely than not that a reporting unit’s fair value is less than its carrying amount before applying the two-step goodwill impairment test for that reporting unit. We assess the impairment of our goodwill based on such qualitative factors as general economic conditions, industry and market conditions, market competiveness, overall financial performance (such as negative cash flows) and other entity specific events. As of December 31, 2014, we concluded that it was more likely than not that the fair value of our reporting units exceeded its carrying value, and as a result, we determined that it was unnecessary to perform any additional testing for goodwill impairment. No goodwill impairment losses were recognized during 2014, 2013 and 2012.

(l) Derivative Instruments

We are exposed to certain risks arising from business operations and economic factors. We use derivative financial instruments to manage exposures that arise from business activities in which our future exposure to interest rate fluctuations is unknown. The objective in the use of an interest rate derivative is to add stability to interest expenses and manage exposure to interest rate changes. We do not use derivatives for trading or speculative purposes and we intend to enter into derivative agreements only with counterparties that we believe have a strong credit rating to mitigate the risk of counterparty default or insolvency. No hedging activity can completely insulate us from the risks associated with changes in interest rates. Moreover, interest rate hedging could fail to protect us or adversely affect us because, among other things:

•

available interest rate hedging may not correspond directly with the interest rate risk for which we seek protection;

•

the duration of the hedge may not match the duration of the related liability;

•

the party owing money in the hedging transaction may default on its obligation to pay; and

•

the credit quality of the party owing money on the hedge may be downgraded to such an extent that it impairs our ability to sell or assign its side of the hedging transaction.

We may designate a derivative as either a hedge of the cash flows from a debt instrument or anticipated transaction (cash flow hedge) or a hedge of the fair value of a debt instrument (fair value hedge). All derivatives are recognized as assets or liabilities at fair value. For effective hedging relationships, the effective portion of the change in the fair value of the assets or liabilities is recorded within equity (cash flow hedge) or through earnings (fair value hedge). Ineffective portions of derivative transactions will result in changes in fair value recognized in earnings. For a cash flow hedge, we record our proportionate share of unrealized gains or losses on our derivative instruments associated with our unconsolidated joint ventures within equity and “Investment in affiliates.” We incorporate credit valuation adjustments to appropriately reflect both our own nonperformance risk and the respective counterparty’s nonperformance risk in the fair value measurements. In adjusting the fair value of our derivative contracts for the effect of nonperformance risk, we have considered the impact of netting any applicable credit enhancements, such as collateral postings, thresholds, mutual inputs and guarantees.

(m) Income Taxes

We have elected to be taxed as a REIT. To maintain our status as a REIT, we are required to distribute at least 90% of our ordinary taxable income annually to our shareholders and meet other organizational and operational requirements. As a REIT, we will not be subject to federal income tax and any non-deductible excise tax if we distribute at least 100% of our REIT taxable income to our shareholders. If we fail to qualify as a REIT in any taxable year, we will be subject to federal income tax on our taxable income at regular corporate tax rates. We have certain subsidiaries, including a taxable REIT subsidiary (“TRS”) and an entity that has elected to be taxed as a REIT (which indirectly owns 500 First Street, NW) that may be subject to federal, state or local taxes, as applicable. A designated REIT will not be subject to federal income tax so long as it meets the REIT qualification requirements and distributes 100% of its REIT taxable income to its shareholders. Our TRS was inactive in 2014, 2013 and 2012. See note 9, Income Taxes, for further information.

We account for deferred income taxes using the asset and liability method. Under this method, deferred income taxes are recognized for temporary differences between the financial reporting basis of assets and liabilities and their respective tax bases and for operating losses, capital losses and tax credit carryovers based on tax rates to be effective when amounts are realized or settled. We will recognize deferred tax assets only to the extent that it is more likely than not that they will be realized based on available evidence, including future reversals of existing temporary differences, future projected taxable income and tax planning strategies. We may recognize a tax benefit from an uncertain tax position when it is more-likely-than-not (defined as a likelihood of more than 50%) that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, based on the technical merits. If a tax position does not meet the more-likely-than-not recognition threshold, despite our belief that our filing position is supportable, the benefit of that tax position is not recognized in the statements of operations. We recognize interest and penalties, as applicable, related to unrecognized tax benefits as a component of income tax expense. We recognize unrecognized tax benefits in the period that the uncertainty is eliminated by either affirmative agreement of the uncertain tax position by the applicable taxing authority, or by expiration of the applicable statute of limitation. For the years ended December 31, 2014, 2013 and 2012, we did not have any uncertain tax positions.

(n) Share-Based Payments

We measure the cost of employee services received in exchange for an award of equity instruments based on the grant-date fair value of the award. For options awards, we use a Black-Scholes option-pricing model. Expected volatility is based on an assessment of our realized volatility over the preceding period that is equivalent to the award’s expected life. The expected term represents the period of time the options are anticipated to remain outstanding as well as our historical experience for groupings of employees that have similar behavior and considered separately for valuation purposes. For non-vested share awards that vest over a predetermined time period, we use the outstanding share price at the date of issuance to fair value the awards. For non-vested shares awards that vest based on performance conditions, we use a Monte Carlo simulation (risk-neutral approach) to determine the value and derived service period of each tranche. The expense associated with the share-based awards will be recognized over the period during which an employee is required to provide services in exchange for the award – the requisite service period (usually the vesting period). The fair value for all share-based payment transactions are recognized as a component of income or loss from continuing operations.

(o) Notes Receivable

We provide loans to the owners of real estate properties, which can be collateralized by interest in the real estate property. We records these loans as “Notes receivable, net” in our consolidated balance sheets. The loans are recorded net of any discount or issuance costs, which are amortized over the life of the respective note receivable using the effective interest method. We record interest earned from notes receivable and amortization of any discount costs or issuance costs within “Interest and other income” in our consolidated statements of operations.

We will establish a provision for anticipated credit losses associated with our notes receivable when we anticipate that we may be unable to collect any contractually due amounts. This determination is based upon such factors as delinquencies, loss experience, collateral quality and current economic or borrower conditions. Our collectability of our notes receivable may be adversely impacted by the financial stability of the Washington, D.C. region and the ability of the underlying assets to keep current tenants or attract new tenants. Estimated losses are recorded as a charge to earnings to establish an allowance for credit losses that we estimate to be adequate based on these factors. Based on the review of the above criteria, we did not record an allowance for credit losses for our notes receivable during 2014, 2013 and 2012.

(p) 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 10, 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 or held-for-sale properties. For more information, see note 2(q), Summary of Significant Accounting Policies - Application of New Accounting Standards.

(q) 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 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 10, 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.

In August 2014, the FASB issued Accounting Standards Update 2014-15, Disclosure of Uncertainties about an Entity's Ability to Continue as a Going Concern (“ASU 2014-15”), which requires an entity to evaluate whether conditions or events, in the aggregate, raise substantial doubt about the entity's ability to continue as a going concern for one year from the date the financial statements are issued or are available to be issued. The guidance will become effective January 1, 2017. The adoption of ASU 2014-15 is not expected to have an impact on our consolidated financial position, results of operations or cash flows.

In January 2015, the FASB issued Accounting Standards Update 2015-01, Income Statement - Extraordinary and Unusual Items (Subtopic 225-20): Simplifying Income Statement Presentation by Eliminating the Concept of Extraordinary Items ("ASU 2015-01"), which eliminates the concept of extraordinary items from U.S. GAAP and the requirement that an entity separately report extraordinary items in the income statement. ASU 2015-01 also requires that entities continue to evaluate whether items are unusual in nature or infrequent in occurrence for presentation and disclosure purposes. ASU 2015-01 applies to all entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2015. Early adoption is permitted and the guidance may be applied prospectively or retrospectively to all prior periods presented in the consolidated financial statements. We believe that the adoption of ASU 2015-01 will not have a material impact on our consolidated statements of operations and related disclosures.

Earnings_Per_Common_Share

Earnings Per Common Share	12 Months Ended
	Dec. 31, 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 are 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):



		2014				2013			2012
	Numerator for basic and diluted earnings per common share:
	Income (loss) from continuing operations	$	15,559			$	(10,761	)	$	(24,324	)

	Income from discontinued operations	1,484				21,742			15,943

	Net income (loss)	17,043				10,981			(8,381		)

	Less: Net (income) loss from continuing operations attributable to noncontrolling interests	(135		)		1,047			1,780

	Less: Net income from discontinued operations attributable to noncontrolling interests	(64		)		(954		)	(794		)
	Net income (loss) attributable to First Potomac Realty Trust	16,844				11,074			(7,395		)

	Less: Dividends on preferred shares	(12,400		)		(12,400		)	(11,964		)
	Net income (loss) attributable to common shareholders	4,444				(1,326		)	(19,359		)

	Less: Allocation to participating securities	(314		)		(388		)	(620		)
	Net income (loss) attributable to common shareholders	$	4,130			$	(1,714	)	$	(19,979	)

	Denominator for basic and diluted earnings per common share:
	Weighted average common shares outstanding – basic	58,150				55,034			50,120

	Weighted average common shares outstanding – diluted	58,220				55,034			50,120

	Basic and diluted earnings per common share:
	Income (loss) from continuing operations	$	0.05			$	(0.41	)	$	(0.70	)

	Income from discontinued operations	0.02				0.38			0.3

	Net income (loss)	$	0.07			$	(0.03	)	$	(0.40	)


	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):



		2014			2013			2012
	Stock option awards	1,122			1,369			1,462

	Non-vested share awards	398			471			553

	Series A Preferred Shares(1)	12,616			12,076			12,162

	14,136			13,916			14,177



(1)	In March 2012, we issued an additional 1.8 million Series A Preferred Shares, which 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	12 Months Ended
	Dec. 31, 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 consists of the following at December 31 (amounts in thousands):



		2014 (1)			2013 (1)
	Land and land improvements	$	325,214		$	287,015

	Buildings and improvements	949,683			807,198

	Construction in progress	69,181			93,174

	Tenant improvements	159,867			138,543

	Furniture, fixtures and equipment	427			4,250

		1,504,372			1,330,180

	Less: accumulated depreciation	(215,499		)	(185,725		)
		$	1,288,873		$	1,144,455



	(1)	Excludes rental property related to properties held-for-sale totaling $57.7 million and $102.4 million at December 31, 2014 and 2013, respectively. For more information, see note 10, Dispositions.

	Depreciation of rental property is computed on a straight-line basis over the estimated useful lives of the assets. The estimated lives of our assets range from 5 to 39 years or, in the case of tenant improvements, the shorter of the useful life of the asset or the term of the underlying lease.

	Development and Redevelopment Activity

	We will place completed development and redevelopment assets in service upon the earlier of one year after major construction activity is deemed to be substantially complete or upon occupancy. We construct office buildings and/or business parks on a build-to-suit basis or with the intent to lease upon completion of construction. We own developable land that can accommodate 1.4 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 expect to complete construction of the new building in the fourth quarter of 2016. At December 31, 2014, our total investment in the development project was $6.9 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 December 31, 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 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 December 31, 2014, our total investment in the development project was $55.4 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 December 31, 2014, the property was 56.8% leased and 36.3% occupied. During the fourth quarter of 2014, all vacant space at the property was placed in-service. At December 31, 2014, our total investment in the redevelopment project was $55.5 million, which included the original cost basis of the property of $23.6 million.

	We did not place-in service any development efforts during 2014. At December 31, 2014, we had no completed development or redevelopment efforts that have yet to be placed in service.

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2014
Business Combinations [Abstract]
Acquisition	Acquisitions

	During 2014 and 2013, we acquired the following properties (dollars in thousands):


	Property	Reporting Segment	Acquisition Date	Property Type	Square Feet	Contractual Purchase Price
	11 Dupont Circle, NW(1)	Washington, DC	September 24, 2014	Office	153,018	$89,000
	1775 Wiehle Avenue(2)	Northern Virginia	June 25, 2014	Office	130,048	$41,000
	1401 K Street, NW(3)	Washington, DC	April 8, 2014	Office	118,292	$58,000
	540 Gaither Road(4)	Maryland	October 1, 2013	Office	133,895	$30,000

	(1) The acquisition was funded with a draw under our unsecured revolving credit facility.
	(2) The acquisition was funded with the net proceeds from the sale of Corporate Campus at Ashburn Center and available cash.
	(3) The acquisition was funded with the assumption of a $37.3 million mortgage loan and a draw under our unsecured revolving credit facility.
	(4) The acquisition was funded with $28.2 million of proceeds from the sale of our industrial portfolio in June 2013 that was previously placed with a qualified intermediary to facilitate a tax-free exchange, as well as available cash.

	For 2014, we included $8.8 million of revenues and $2.0 million of net loss 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 $2.7 million and $0.6 million of acquisition-related due diligence and closing costs during 2014 and 2013, respectively.

	The fair values of the net assets acquired in 2014 are as follows (amounts in thousands):



		2014				2013
	Land	$	48,792			$	6,458

	Acquired tenant improvements	10,857				1,669

	Building and improvements	111,173				18,162

	In-place leases	12,540				2,886

	Acquired leasing commissions	4,681				580

	Legal leasing fees	360				2

	Above-market leases acquired	2,397				243

	Total assets acquired	190,800				30,000

	Below-market leases assumed	(2,800		)		—

	Debt assumed	(37,269		)		—

	Net assets acquired	$	150,731			$	30,000


	The fair values for the assets acquired in 2014 are preliminary as we continue to finalize their acquisition date fair value determination.

	At December 31, 2014, our consolidated intangible assets acquired 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 4.3 years. During the fourth quarter of 2014, we accelerated the amortization of lease-level assets and liabilities associated with a tenant at 1401 K Street, NW, who vacated effective January 2015. The accelerated amortization for the three months ended December 31, 2014 resulted in a net increase in depreciation and amortization expense of $0.1 million, which included a $0.6 million decrease in depreciation and amortization related to the aggregate deferred market assets and liabilities.



	Pro Forma Financial Information (unaudited)

	The unaudited pro forma financial information set forth below presents results for the twelve months ended December 31, 2014 and 2013 as if all of our 2014 and 2013 acquisitions (1401 K Street, NW, 1775 Wiehle Avenue, 11 Dupont Circle, NW and 540 Gaither Road), and related financings, 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 (amounts in thousands, except per share amounts):



		2014				2013
	Pro forma total revenues	$	171,686			$	170,800

	Pro forma net income	$	19,461			$	5,572

	Pro forma net income (loss) per share – basic and diluted	$	0.12			$	(0.12	)

Investment_in_Affiliates

Investment in Affiliates	12 Months Ended
	Dec. 31, 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, liabilities and operating results of these noncontrolled joint ventures are not consolidated within our 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 at December 31 (dollars in thousands):



				2014
		Reporting Segment		Ownership			Company				Debt			Recourse
				Interest			Investment							Debt(1)
	Prosperity Metro Plaza	Northern Virginia		51	%		$	24,651			$	50,000	(2)	$	—

	1750 H Street, NW	Washington, D.C.		50	%		14,834				32,000		(2)	—

	Aviation Business Park	Maryland		50	%		5,748				—			—

	Rivers Park I and II(3)	Maryland		25	%		2,249				28,000		(2)	2,800

							$	47,482			$	110,000		$	2,800


				2013
		Reporting Segment		Ownership			Company				Debt			Recourse
				Interest			Investment							Debt(1)
	Prosperity Metro Plaza	Northern Virginia		51	%		$	24,735			$	48,991	(4)	$	—

	1750 H Street, NW	Washington, D.C.		50	%		16,780				28,413		(4)	—

	Aviation Business Park	Maryland		50	%		5,008				—			—

	Rivers Park I and II(3)	Maryland		25	%		2,627				28,000			7,000

							$	49,150			$	105,404		$	7,000



	(1)	We believe the fair value of the potential liability to us related to the recourse debt is inconsequential as the likelihood of our need to perform under the debt agreement is remote.

	(2)	During 2014, the mortgage loans that encumbered Prosperity Metro Plaza and 1750 H Street, NW matured and were replaced with new mortgage loans and the mortgage loan that encumbered Rivers Park I and II was refinanced. See below for details.

	(3)	Rivers Park I and Rivers Park II are owned through two separate joint ventures.

	(4)	Excludes the unamortized fair value adjustments recorded at acquisition upon the assumption of the mortgage loans.

	On November 12, 2014, our 51% owned unconsolidated joint venture repaid a $48.3 million mortgage loan that encumbered Prosperity Metro Plaza, a two-building, 327,000 square-foot office building located in Merrifield, Virginia. Simultaneously with the repayment, the joint venture entered into a new $50.0 million mortgage loan that has a fixed-interest rate of 3.91%. The new loan requires interest only payments through December 2024, at which time the loan requires principal and interest payments through its maturity date. The loan has a maturity date of December 1, 2029 and is repayable in full without penalty on or after June 1, 2029.

	On September 26, 2014, our 25% owned unconsolidated joint venture amended a $28.0 million mortgage loan that encumbers Rivers Park I and II, a six-building, 308,000 square-foot business park located in Columbia, Maryland. The amended mortgage loan reduced the variable interest rate spread by 60 basis points and reduced the amount of outstanding principal recourse to us from 25% to 10%. The amended loan matures on September 26, 2017 and is repayable in full without penalty at any time during the term of the loan.

	On July 10, 2014, our 50% owned unconsolidated joint venture repaid a $27.9 million mortgage loan that encumbered 1750 H Street, NW, a ten-story, 113,000 square-foot office building located in Washington, D.C. Simultaneously with the repayment, the joint venture entered into a new $32.0 million mortgage loan that has a fixed interest rate of 3.92%, a maturity date of August 1, 2024, and is repayable in full without penalty on or after August 1, 2021. The new loan requires monthly interest-only payments with a constant interest rate over the life of the loan.

	The net assets of our unconsolidated joint ventures consisted of the following at December 31 (dollars in thousands):


		2014				2013
	Assets:
	Rental property, net	$	193,533			$	194,240

	Cash and cash equivalents	4,567				3,680

	Other assets	16,748				15,585

	Total assets	214,848				213,505

	Liabilities:
	Mortgage loans(1)	110,000				106,384

Other liabilities	7,256				5,046

Total liabilities	117,256				111,430

Net assets	$	97,592			$	102,075



(1)	The 2013 figures include the unamortized fair value adjustments recorded at acquisition upon the assumption of mortgage loans. During 2014, the mortgage loans that encumbered Prosperity Metro Plaza and 1750 H Street, NW matured and were replaced with new mortgage loans and the mortgage loan that encumbered Rivers Park I and II was refinanced. See above for details.

Our share of earnings or losses related to our unconsolidated joint ventures is recorded in our consolidated statements of operations as “Equity in (earnings) losses of affiliates.”

The following table summarizes the results of operations of our unconsolidated joint ventures at December 31, 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 (amounts in thousands):



	2014				2013				2012
Total revenues	$	23,285			$	24,017			$	24,945

Total operating expenses	(7,408		)		(7,753		)		(7,377		)
Net operating income	15,877				16,264				17,568

Depreciation and amortization	(9,893		)		(11,551		)		(12,564		)
Interest expense, net	(3,890		)		(4,222		)		(4,326		)
Provision for income taxes	(63		)		(83		)		(21		)
Contingent consideration charge	126				—				—

Net income	$	2,157			$	408			$	657


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 $0.7 million, $0.6 million and $0.5 million in 2014, 2013 and 2012, respectively, which are reflected within “Tenant reimbursements and other revenues” in our consolidated statements of operations.

Notes_Receivable

Notes Receivable	12 Months Ended
	Dec. 31, 2014
Receivables [Abstract]
Notes Receivable	Notes Receivable

	Below is a summary of our notes receivable for our outstanding mezzanine loans at December 31, 2014 and 2013 (dollars in thousands):



		Balance at December 31, 2014
	Property	Face Amount		Unamortized			Balance		Interest Rate
				Origination Fees
	950 F Street, NW	$	34,000	$	—		$	34,000	9.75	%

	America's Square	29,720		(41		)	29,679		9	%

		$	63,720	$	(41	)	$	63,679




		Balance at December 31, 2013
	Property	Face Amount		Unamortized			Balance		Interest Rate
				Origination Fees
	950 F Street, NW	$	25,000	$	(130	)	$	24,870	12.5	%

	America's Square	29,896		(70		)	29,826		9	%

		$	54,896	$	(200	)	$	54,696


	We provided the owners of America Square, a 461,000 square foot office complex located in Washington, D.C., a $30.0 million loan in April 2011. On January 27, 2015, the owners of America’s Square gave notice of their intent to prepay the mezzanine loan which has an outstanding balance of $29.7 million. We anticipate the loan will be repaid on or about February 24, 2015. The loan, which was secured by a portion of the owners’ interest in the property, 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 loan had a May 1, 2016 maturity date and was repayable in full at any time, subject to yield maintenance. We expect to receive a yield maintenance payment of $2.4 million with the repayment of the loan. The proceeds from the loan repayment will be used to pay down a portion of the outstanding balance under our unsecured revolving credit facility.

	In December 2010, we provided a $25.0 million mezzanine loan to the owners of 950 F Street, NW, a ten-story, 287,000 square-foot, office/retail building located in Washington, D.C. that is secured by a portion of the owners’ interest in the property. The loan requires monthly interest-only payments with a constant interest rate over the life of the loan. On January 10, 2014, we amended the loan to increase the outstanding balance to $34.0 million and reduce the fixed interest rate from 12.5% to 9.75%. The amended mezzanine loan matures on April 1, 2017 and is repayable in full on or after December 21, 2015. The $9.0 million increase in the loan was provided by a draw under our unsecured revolving credit facility.

	We recorded interest income related to our notes receivable of $6.1 million during 2014 and $5.9 million during both 2013 and 2012, which is included within “Interest and other income” in our consolidated statements of operations. Payments under both loans were current at December 31, 2014.

	We recorded income from the amortization of origination fees of $32 thousand in 2014 and $0.1 million for both 2013 and 2012. 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 origination fees are recorded within “Interest and other income” in our consolidated statements of operations.

Intangible_Assets_and_Deferred

Intangible Assets and Deferred Market Rent Liabilities	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets and Deferred Market Rent Liabilities	Intangible Assets and Deferred Market Rent Liabilities

	Intangible assets and deferred market rent liabilities consisted of the following at December 31 (amounts in thousands):



		2014(1)							2013(1)
		Gross		Accumulated			Net		Gross		Accumulated			Net
		Intangibles		Amortization			Intangibles		Intangibles		Amortization			Intangibles
	In-place leases	$	51,258	$	(22,443	)	$	28,815	$	44,772	$	(18,843	)	$	25,929

	Customer relationships	906		(654		)	252		1,002		(591		)	411

	Leasing commissions	11,335		(4,272		)	7,063		7,796		(3,361		)	4,435

	Legal leasing fees	377		(118		)	259		137		(83		)	54

	Deferred market rent assets	3,906		(1,309		)	2,597		2,485		(1,348		)	1,137

	Goodwill	6,930		—			6,930		6,930		—			6,930

		$	74,712	$	(28,796	)	$	45,916	$	63,122	$	(24,226	)	$	38,896

	Deferred market rent liability	$	5,193	$	(2,348	)	$	2,845	$	4,381	$	(2,767	)	$	1,614



	(1)	Includes amounts from properties that were classified as held-for-sale at December 31, 2014 and 2013.

	We recognized $10.3 million, $8.3 million and $10.7 million of amortization expense on intangible assets for the years ended December 31, 2014, 2013 and 2012, respectively. We recognized $14 thousand of additional rental revenue through the net amortization of deferred market rent assets and deferred market rent liabilities for the year ended December 31, 2014. For the years ended December 31, 2013 and 2012, we recognized a reduction of rental revenue of $0.1 million and $0.2 million, respectively, through the net amortization of deferred market rent assets and deferred market rent liabilities. Losses due to termination of tenant leases and defaults, which resulted in the write-offs of all lease-level and intangible assets, were $1.1 million, $1.0 million and $1.1 million during 2014, 2013 and 2012, respectively.

	The projected net amortization of intangible assets and deferred market liabilities as of December 31, 2014, including amounts from properties that were classified as held-for-sale at December 31, 2014, are as follows (amounts in thousands):



	2015	$	10,747

	2016	8,745

	2017	4,275

	2018	2,707

	2019	2,393

	Thereafter	7,274

		$	36,141

Income_Taxes

Income Taxes	12 Months Ended
Income Taxes	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes

	We own properties in Washington, D.C. that are subject to income-based franchise taxes at an effective rate of 9.975% as a result of conducting business in Washington, D.C. Our deferred tax assets and liabilities associated with our properties were primarily associated with differences in the GAAP and tax basis of rental property, particularly acquisition costs, but also included intangible assets and deferred market rent assets and liabilities that were associated with properties located in Washington, D.C. We will recognize deferred tax assets only to the extent that it is more likely than not that deferred tax assets will be realized based on consideration of available evidence, including future reversals of existing taxable temporary differences, future projected taxable income and tax planning strategies.

	During the third quarter of 2012, there was a change in tax regulations in the District of Columbia that required us to file a unitary tax return, which allowed for a deduction for dividends paid to shareholders. The change in tax regulations resulted in us prospectively measuring all of our deferred tax assets and deferred tax liabilities using the effective tax rate 0% expected to be in effect as these timing differences reverse; therefore, we did not record a benefit from income taxes during 2014 or 2013. We recognized a benefit from income taxes of $4.1 million during 2012. At December 31, 2014 and 2013, we recorded a $1.0 million receivable within “Accounts and other receivables” in our consolidated balance sheets for an expected tax refund associated with our 2011 tax payments and the estimated payments made in 2012 arising from the change in regulations in 2012. At December 31, 2014 and 2013, we did not have any recorded deferred tax assets or deferred tax liabilities. We also have interests in an unconsolidated joint venture that owns rental property in Washington, D.C. that is subject to the franchise tax. The impact for income taxes related to this unconsolidated joint venture is reflected within “Equity in (earnings) losses of affiliates” in our consolidated statements of operations.

	We did not record a valuation allowance against our deferred tax assets for any period presented. We did not recognize any deferred tax assets or liabilities as a result of uncertain tax positions and had no material net operating loss, capital loss or alternative minimum tax carryovers. There was no benefit or provision for income taxes associated with our discontinued operations for any period presented.

	As we believe we both qualify as a REIT and will not be subject to federal income tax, a reconciliation between the income tax provision calculated at the statutory federal income tax rate and the actual income tax provision has not been provided.

Dispositions

Dispositions	12 Months Ended
	Dec. 31, 2014
Discontinued Operations and Disposal Groups [Abstract]
Discontinued Operations	Dispositions

	During the second quarter of 2014, we prospectively adopted ASU 2014-08, which states that a component of an entity or a group of components of an entity is required to be reported in discontinued operations only if the disposal represents a strategic shift that has, or will have, a major effect on an entity’s operations and financial results. All other disposed properties will have their operating results reflected within continuing operations on our consolidated statements of operations for all periods presented. For more information, see note 2(q), 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 (dollars in thousands):



		Reporting	Disposition Date	Property Type	Square Feet		Net Sale Proceeds
		Segment
	Owings Mills Business Park	Maryland	10/16/14	Business Park	180,475		$	12,417

	Corporate Campus at Ashburn Center	Northern Virginia	6/26/14	Business Park	194,184		39,910


	In accordance with ASU 2014-08, which we prospectively adopted during the second quarter of 2014, the operating results 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 the two properties that are included in continuing operations for the periods presented (dollars in thousands):



		2014				2013				2012
	Revenues	$	2,920			$	5,223			$	5,363

	Property operating expenses	(1,172		)		(1,521		)		(1,375		)
	Depreciation and amortization	(1,047		)		(1,424		)		(1,517		)
	Interest expense, net of interest income	—				—				(230		)

	Impairment of rental property	(3,956		)		—				(3,246		)

	(Loss) income from operations of disposed property	(3,255		)		2,278				(1,005		)

	Loss on debt extinguishment	—				—				(466		)

	Gain on sale of rental property	21,230				—				—

	Net income (loss) from continuing operations	$	17,975			$	2,278			$	(1,471	)


	(b) Discontinued Operations
	Effective as of February 9, 2015, we entered into a binding contract to sell our Richmond, Virginia portfolio, which is located in our Southern Virginia reporting segment. The Richmond Portfolio consists of Chesterfield Business Center, Hanover Business Center, Park Central, Virginia Technology Center and a three-acre parcel of undeveloped land, and in the aggregate is comprised of 19 buildings totaling 827,900 square feet. We anticipate closing the sale in the first half of 2015. However, we can provide no assurances regarding the timing or pricing of the sale of the Richmond Portfolio, or that the sale will occur at all. With the sale of our Richmond Portfolio, we will no longer own any properties in the Richmond, Virginia area and will have strategically exited the Richmond market. As such, in accordance with ASU 2014-08, our Richmond Portfolio was classified as held-for-sale at December 31, 2014 and the operating results of the Richmond Portfolio are reflected within discontinued operations for each of the periods presented.

	At December 31, 2014, the Richmond Portfolio 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, along with five mortgage loans that will be repaid, were classified within “Liabilities-held-for-sale” in our consolidated balance sheet. The majority of the assets classified within “Assets held-for sale” at December 31, 2014, consisted of $7.7 million in land, $62.0 million in buildings, $8.5 million in tenant improvements, $0.1 million in construction in progress and accumulated depreciation of $20.6 million. The remaining $2.0 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, prepaid expenses and other assets, and intangible assets, net of accumulated amortization. The majority of "Liabilities held-for-sale" at December 31, 2014 consisted of $3.5 million of mortgage debt. The remaining $1.1 million classified within "Liabilities held-for-sale" consisted of prepaid rent and security deposits.
	In addition to the Richmond Portfolio, all properties sold prior to our adoption of ASU 2014-08 or classified as held-for-sale in previously issued consolidated financial statements prior to our adoption of ASU 2014-08, are classified within discontinued operations.

	As of December 31, 2013, the assets of the Richmond Portfolio, together with the Patrick Center, West Park, Girard Business Center and Gateway Center properties were classified within “Assets held-for-sale” and the liabilities of the buildings, along with the Richmond Portfolio mortgage debt that will be repaid, were classified within “Liabilities-held-for-sale” in our consolidated balance sheet. The majority of the assets classified within “Assets held-for sale” as of December 31, 2013, consisted of $21.4 million in land, $97.5 million in building, $12.8 million in tenant improvements, $0.1 million in construction in progress and accumulated depreciation of $29.4 million. The remaining $4.1 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, prepaid expenses and other assets, and intangible assets, net of accumulated amortization. The majority of "Liabilities held-for-sale" at December 31, 2013, consisted of $4.5 million of mortgage debt. The remaining $1.0 million classified within "Liabilities held-for-sale" consisted of prepaid rent and security deposits. At December 31, 2013, the Richmond Portfolio did not meet our held-for-sale criteria and, therefore, we did not cease recording depreciation until December 31, 2014, when the property met our held-for-sale criteria. We classified the assets and liabilities as held-for-sale on our December 31, 2013 consolidated balance sheet in accordance with the standards set forth in ASU 2014-08.

	The following table is a summary of completed and anticipated property dispositions whose operating results are reflected as discontinued operations in our consolidated statements of operations for the periods presented (dollars in thousands):



		Reporting Segment		Disposition		Property Type		Square			Net Sale
				Date				Feet			Proceeds
	Richmond Portfolio(1)	Southern Virginia		TBD		Business Park		827,900			$ N/A

	Patrick Center	Maryland		4/16/14		Office		66,269			10,888

	West Park	Maryland		4/2/14		Office		28,333			2,871

	Girard Business Center and Gateway Center	Maryland		1/29/14		Business Park and Office		341,973			31,616

	Worman’s Mill Court	Maryland		11/19/13		Office		40,099			3,362

	Triangle Business Center	Maryland		9/27/13		Business Park		74,429			2,732

4200 Tech Court	Northern Virginia		8/15/13		Office		33,875			3,210

Industrial Portfolio(2)	Various		May/June 2013		Industrial		4,280,985			176,569

4212 Tech Court	Northern Virginia		6/5/13		Office		32,055			2,469

Owings Mills Business Park(3)	Maryland		11/7/12		Business Park		38,779			3,472

Goldenrod Lane	Maryland		5/31/12		Office		23,518			2,663

Woodlands Business Center	Maryland		5/8/12		Office		37,887			2,885

Airpark Place Business Center	Maryland		3/22/12		Business Park		82,429			5,153



(1)	Effective as of February 9, 2015, we entered a binding contract to sell the Richmond Portfolio, which we anticipate closing in the first half of 2015. However, we can provide no assurances regarding the timing or pricing of the sale of the Richmond Portfolio, or that the sale will occur at all. We classified the Richmond Portfolio as held-for-sale at December 31, 2014.

(2)	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.

(3)	In November 2012, we sold two of the six buildings at Owings Mills Business Park. The remaining four buildings at Owings Mills Business Park were sold in October 2014 and their results of operations are included in continuing operations in our consolidated statements of operations. See note 10(a) Dispositions - Disposed or Held-for-Sale Properties within Continuing Operations.

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 2014, 2013 and 2012.

The following table summarizes the results of operations of properties included in discontinued operations for the years ended December 31 (dollars in thousands):



	2014				2013				2012

Revenues	$	7,688			$	31,654			$	50,985

Property operating expenses	(3,612		)		(10,564		)		(16,226		)

Depreciation and amortization	(3,662		)		(8,937		)		(14,958		)

Interest expense, net of interest income	(268		)		(1,268		)		(2,947		)

Impairment of rental property	—				(4,092		)		(1,072		)

Income from operations of disposed property	146				6,793				15,782

Loss on debt extinguishment	—				(4,414		)		—

Gain on sale of rental property	1,338				19,363				161

Net income from discontinued operations	$	1,484			$	21,742			$	15,943

Debt

Debt	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Debt	Debt

	Our borrowings consisted of the following at December 31 (dollars in thousands):



		2014				2013
	Mortgage loans, effective interest rates ranging from 4.40% to 6.63%, maturing at various dates through June 2023(1)(2)	$	308,637			$	274,648

	Unsecured term loan, effective interest rates ranging from LIBOR plus 1.65% to LIBOR plus 2.05%, with staggered maturity dates ranging from October 2018 to October 2020(1)	300,000				300,000

	Unsecured revolving credit facility, effective interest rate of LIBOR plus 1.70%, maturing October 2017(1)	205,000				99,000

		$	813,637			$	673,648



	(1)	At December 31, 2014, LIBOR was 0.17%. All references to LIBOR in the consolidated financial statements refer to one-month LIBOR.

	(2)	Includes five mortgage loans that will be repaid upon the sale of the Richmond Portfolio, which is expected to be sold in the first half of 2015. At December 31, 2014 and 2013, the mortgage loans had an aggregate principal balance of $3.5 million and $4.5 million, respectively, and were classified within “Liabilities held-for-sale” on our consolidated balance sheets for the periods presented.


	(a) Mortgage Loans

	The following table provides a summary of our mortgage debt at December 31, 2014 and 2013 (dollars in thousands):



	Encumbered Property	Contractual			Effective			Maturity		31-Dec-14				31-Dec-13
		Interest Rate			Interest			Date
					Rate
	Annapolis Business Center(1)	5.74	%		6.25	%		Jun-14		$	—			$	8,076

	Jackson National Life Loan(2)	5.19	%		5.19	%		Aug-15		64,943				66,116

	440 First Street, NW Construction Loan(3)(4)	LIBOR + 2.50%			LIBOR + 2.50%			May-16		32,216				21,699

	Storey Park Land Loan(3)(5)	LIBOR + 2.50%			LIBOR + 2.50%			Oct-16		22,000				22,000

	Gateway Centre Manassas Building I	7.35	%		5.88	%		November 2016		432				638

	Hillside I and II	5.75	%		4.62	%		December 2016		12,949				13,349

	Redland Corporate Center Buildings II & III	4.2	%		4.64	%		Nov-17		65,816				67,038

	840 First Street, NE	5.72	%		6.01	%		Jul-20		36,539				37,151

	Battlefield Corporate Center	4.26	%		4.4	%		Nov-20		3,692				3,851

	1211 Connecticut Avenue, NW	4.22	%		4.47	%		Jul-22		29,691				30,249

	1401 K Street, NW	4.8	%		4.93	%		Jun-23		36,861				—

					4.75	%	(6)			305,139				270,167

	Unamortized fair value adjustments									(370		)		(554		)
	Principal balance									304,769				269,613


	Richmond Portfolio(7)
	Hanover Business Center Building D	8.88	%		6.63	%		Aug-15		104				252

	Chesterfield Business Center Buildings C,D,G and H	8.5	%		6.63	%		Sep-15		302				681

Hanover Business Center Building C	7.88	%		6.63	%		Dec-17		505				653

Chesterfield Business Center Buildings A,B,E and F	7.45	%		6.63	%		Jun-21		1,674				1,873

Airpark Business Center	7.45	%		6.63	%		Jun-21		913				1,022

									3,498				4,481

Total unamortized fair value adjustments - Richmond(3)									(73		)		(109		)
Total principal balance - Richmond(3)									$	3,425			$	4,372


Total principal balance				4.75	%	(6)			$	308,194			$	273,985



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

(2)	At December 31, 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 December 31, 2014, LIBOR was 0.17%.

(4)	At December 31, 2014, 50% of the principal balance and any unpaid accrued interest on the 440 First Street, NW construction loan were recourse to us. In 2014, we borrowed an additional $10.5 million under the construction loan.

(5)	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.

(6)	Weighted average interest rate on total mortgage debt.

(7)	The mortgage loans that encumber properties within the Richmond Portfolio were classified within “Liabilities held-for-sale” on our consolidated balance sheets for the periods presented and will be repaid upon the sale of the Richmond Portfolio, which is expected to be sold in the first half of 2015.


Land Loan
On October 16, 2014, our 97% owned consolidated joint venture that owns Storey Park repaid a $22.0 million loan that encumbered the Storey Park land and was subject to a 5.0% interest rate floor. Simultaneously with the repayment, the joint venture entered into a new $22.0 million land loan with a variable interest rate of LIBOR plus 2.50%. The new loan matures on October 16, 2016, with a one-year extension at our option, and is repayable in full without penalty at any time during the term of the loan. Per the terms of the loan agreement, $6.0 million of the outstanding principal balance and all of the outstanding accrued interest is recourse to us. As of December 31, 2014, we were in compliance with all the financial covenants of the Storey Park land loan.

Construction Loan

On June 5, 2013, we entered into a construction loan (the “Construction Loan”) that is collateralized by our 440 First Street, NW property, which underwent a major redevelopment that was substantially completed in October 2013. The Construction Loan has a borrowing capacity of up to $43.5 million, of which we initially borrowed $21.7 million in the second quarter of 2013 and borrowed an additional $10.5 million in 2014. The Construction Loan has a variable interest rate of LIBOR plus a spread of 2.50% 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 December 31, 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 December 31, 2014, we were in compliance with all the financial covenants of the Construction Loan.

With the exception of the specific debt instruments identified in the above table, our mortgage debt is recourse solely to specific assets. We had 18 consolidated properties that secured mortgage debt at December 31, 2014 and 2013.

We have originated or assumed the following mortgage loans since January 1, 2013 (dollars in thousands):



Month		Year		Property		Effective			Principal
						Interest			Amount
						Rate
October		2014		Storey Park Land Loan(1)		LIBOR + 2.50%			$	22,000		(1)

April		2014		1401 K Street, NW		4.93	%		37,269

June		2013		440 First Street, NW Construction Loan(2)		5	%		21,699			(2)



(1)	We have a 97% ownership interest in the property through a consolidated joint venture. The loan balance in the chart above reflects the entire loan balance, which is reflected in our consolidated balance sheets.

(2)	At December 31, 2014, 50% of the principal balance and any unpaid accrued interest on the 440 First Street, NW construction loan were recourse to us. In 2014, we borrowed an additional $10.5 million under the construction loan.

We have repaid the following mortgage loans since January 1, 2013 (dollars in thousands):



Month		Year		Property		Effective			Principal
						Interest			Balance
						Rate			Repaid
October		2014		Storey Park Land Loan		5.8	%		$	22,000

May		2014		Annapolis Business Center		6.25	%		8,027

September		2013		840 First Street, NE(1)		6.05	%		53,877

September		2013		Linden Business Center		5.58	%		6,622

June		2013		Cloverleaf Center		6.75	%		16,427

June		2013		Mercedes Center – Note 1		6.04	%		4,799

June		2013		Mercedes Center – Note 2		6.3	%		9,260

June		2013		Jackson National Life Loan -Northridge		5.19	%		6,985

May		2013		Jackson National Life Loan - I-66 Commerce Center		5.19	%		21,695

February		2013		1434 Crossways Boulevard, Building I		5.38	%		7,597

February		2013		TenThreeTwenty		7.29	%		13,273

February		2013		Cedar Hill		6.58	%		15,364

January		2013		Prosperity Business Center		5.75	%		3,242



(1)	On September 30, 2013, we repaid a $53.9 million mortgage loan that encumbered 840 First Street, NE, which was scheduled to mature on October 1, 2013. Simultaneously with the repayment of the mortgage debt, we encumbered 840 First Street, NE with a $37.3 million mortgage loan that had previously encumbered 500 First Street, NW.

(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 December 31, 2014 (dollars in thousands):


	Maturity Date		Amount				Interest Rate(1)
Tranche A	Oct-18		$	100,000			LIBOR, plus 165 basis points

Tranche B	Oct-19		100,000				LIBOR, plus 180 basis points

Tranche C	October 2020		100,000				LIBOR, plus 205 basis points

			$	300,000


(1)	At December 31, 2014, LIBOR was 0.17%. The interest rate spread is subject to change based on our maximum total indebtedness ratio. For more information, see note 11(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 December 31, 2014, we were in compliance with all the financial covenants of the unsecured term loan.

(c) Unsecured Revolving Credit Facility

The weighted average borrowings outstanding under the unsecured revolving credit facility were $136.1 million with a weighted average interest rate of 1.7% during 2014 compared with $139.4 million and 2.6%, respectively, during 2013. Our maximum outstanding borrowings were $216.0 million and $245.0 million during 2014 and 2013, respectively. At December 31, 2014, outstanding borrowings under the unsecured revolving credit facility were $205.0 million with a weighted average interest rate of 1.9%. At December 31, 2014, LIBOR was 0.17% and the applicable spread on our unsecured revolving credit facility was 170 basis points. The available capacity under the unsecured revolving credit facility was $79.0 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. For more information, see note 11(e) Debt – Financial Covenants. As of December 31, 2014, we were in compliance with all the financial covenants of the unsecured revolving credit facility.

(d) Interest Rate Swap Agreements

At December 31, 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. In January 2014, an interest rate swap that fixed LIBOR on $50.0 million of variable rate debt expired. See note 12, 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 December 31, 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 and the Storey Park land loan).

Our continued ability to borrow under the unsecured revolving credit facility is subject to compliance with financial and operating covenants, and a failure to comply with any of these covenants could result in a default under the credit facility. These debt agreements also contain cross-default provisions that would be triggered if we were in default under other loans, including mortgage loans, in excess of certain amounts. In the event of a default, the lenders could accelerate the timing of payments under the debt obligations and we may be required to repay such debt with capital from other sources, which may not be available on attractive terms, or at all, which would have a material adverse effect on our liquidity, financial condition, results of operations and ability to make distributions to our shareholders.


Our unsecured revolving credit facility and unsecured term loan are subject to interest rate spreads that float based on the quarterly measurement of our maximum consolidated total indebtedness to gross asset value ratio. Based on our leverage ratio at December 31, 2014, the applicable interest rate spreads on the unsecured revolving credit facility and the unsecured term loan will be unchanged.

(f) Aggregate Debt Maturities

Our aggregate debt maturities as of December 31, 2014, including amounts from properties that were classified as held-for-sale at December 31, 2014, are as follows (dollars in thousands):



2015		$	69,553

2016		70,763

2017		270,999

2018		102,746

2019		102,894

Thereafter		196,239

		813,194

Unamortized fair value adjustments		443

Total contractual principal balance		$	813,637

Derivative_Instruments

Derivative Instruments	12 Months Ended
	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments	Derivative Instruments

	Our interest rate swap agreements are designated as cash flow hedges and we record the effective portion of any unrealized gains associated with the change in fair value of the swap agreements within “Accumulated other comprehensive loss” and “Prepaid expenses and other assets” and the effective portion of any unrealized losses within “Accumulated other comprehensive loss” and “Accounts payable and other liabilities” on our consolidated balance sheets. We record our proportionate share of any unrealized gains or losses on our cash flow hedges associated with our unconsolidated joint ventures within “Accumulated other comprehensive loss” and “Investment in affiliates” on our consolidated balance sheets. We record any gains or losses incurred as a result of each interest rate swap agreement’s fixed rate deviating from our respective loan’s contractual rate within “Interest expense” in our consolidated statements of operations. We did not have any material ineffectiveness associated with our cash flow hedges in 2014, 2013 and 2012.

	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 December 31, 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):



	Maturity Date	Notional		Interest Rate	Fixed LIBOR
		Amount		Contractual	Interest Rate
				Component
	Jul-16	$	35,000	LIBOR	1.754	%

	Jul-16	25,000		LIBOR	1.763	%

	Jul-17	30,000		LIBOR	2.093	%

	Jul-17	30,000		LIBOR	2.093	%

	Jul-18	30,000		LIBOR	1.66	%

	Jul-18	25,000		LIBOR	1.394	%

	Jul-17	25,000		LIBOR	1.129	%

	Jul-17	12,500		LIBOR	1.129	%

	Jul-18	12,500		LIBOR	1.383	%

	Jul-17	50,000		LIBOR	0.955	%

	Jul-18	25,000		LIBOR	1.135	%

	Total/Weighted Average	$	300,000		1.505	%


	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 $4.1 million, $4.6 million and $4.2 million in 2014, 2013 and 2012, respectively. As of December 31, 2014, we estimate that $3.3 million of our accumulated other comprehensive loss will be reclassified as an increase to interest expense over the following twelve months.

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 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 December 31, 2014 and 2013 (amounts in thousands):



		Balance at December 31, 2014			Level 1			Level 2			Level 3
	Recurring Measurements:
	Derivative instrument-swap assets	$	133		$	—		$	133		$	—

	Derivative instrument-swap liabilities	3,569			—			3,569			—




		Balance at December 31, 2013			Level 1			Level 2			Level 3
	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			—


	With the exception of a contingent consideration obligation, which totaled $39 thousand at December 31, 2013, 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 years ended December 31, 2014 and 2013. During the first quarter of 2014, we issued 3,125 common Operating Partnership units to the seller of 840 First Street, NE to satisfy our contingent consideration obligation. 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 years ended December 31, 2014 and 2013.

	Impairment of Rental Property

	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.

	During the fourth quarter of 2013, we were in negotiations with a buyer to sell our West Park property, which was located in our Maryland reporting segment. Based on the anticipated sales price, we recorded an impairment charge of $2.2 million in the fourth quarter of 2013. In April 2014, we sold our West Park property.

	We incurred impairment charges of $4.0 million, $4.1 million and $3.5 million during 2014, 2013 and 2012, respectively. Of the total impairment charges, $4.0 million and $2.4 million incurred during 2014 and 2012, respectively, were related to four buildings at Owings Mills Business Park, and are reflected within continuing operations in our consolidated statements of operations. The impairment charges incurred during 2013 and the remaining impairment charges incurred during 2012 relate to properties that were subsequently disposed of at December 31, 2014 and are recorded within discontinued operations in our consolidated statements of operations. See note 10, Dispositions for more information.

	Interest Rate Derivatives

	At December 31, 2014, we had hedged $300.0 million of our variable rate debt through eleven interest rate swap agreements. See note 12, Derivative Instruments, for more information about our interest rate swap agreements.

	The interest rate derivatives are fair valued based on prevailing market yield curves on the measurement date and also incorporate credit valuation adjustments to appropriately reflect both our own nonperformance risk and the respective counterparty’s nonperformance risk in the fair value measurements. In adjusting the fair value of our derivative contracts for the effect of nonperformance risk, we have considered the impact of netting any applicable credit enhancements, such as collateral postings, thresholds, mutual inputs and guarantees. We use a third party to assist in valuing our interest rate swap agreements. A daily “snapshot” of the market is taken to obtain close of business rates. The snapshot includes over 7,500 rates including LIBOR fixings, Eurodollar futures, swap rates, exchange rates, treasuries, etc. This market data is obtained via direct feeds from Bloomberg and Reuters and from Inter-Dealer Brokers. The selected rates are compared to their historical values. Any rate that has changed by more than normal mean and related standard deviation would be considered an outlier and flagged for further investigation. The rates are then compiled through a valuation process that generates daily valuations, which are used to value our interest rate swap agreements. Our interest rate swap derivatives are effective cash flow hedges and the effective portion of the change in fair value is recorded in the equity section of our consolidated balance sheets as “Accumulated other comprehensive loss.”




	Financial Instruments

	The carrying amounts of cash equivalents, accounts and other receivables, accounts payable and other liabilities, with the exception of any items listed above, approximate their fair values due to their short-term maturities. We determine the fair value of our notes receivable and debt instruments by discounting future contractual principal and interest payments using prevailing market rates for securities with similar terms and characteristics at the balance sheet date. We deem the fair value measurement of our debt instruments as a Level 2 measurement as we use quoted interest rates for similar debt instruments to value our debt instruments. We also use quoted market interest rates for similar notes to value our notes receivable, which we consider a Level 2 measurement as we do not believe notes receivable trade in an active market.

	The carrying amount and estimated fair value of our notes receivable and debt instruments at December 31 are as follows (amounts in thousands):



	2014						2013
	Carrying			Fair			Carrying			Fair
	Value			Value			Value			Value
Financial Assets:
Notes receivable(1)	$	63,679		$	63,720		$	54,696		$	56,812

Financial Liabilities:
Mortgage debt(2)	$	308,637		$	292,882		$	274,648		$	262,873

Unsecured term loan	300,000			300,000			300,000			300,000

Unsecured revolving credit facility	205,000			205,000			99,000			99,000

Total	$	813,637		$	797,882		$	673,648		$	661,873



(1)	The principal amount of our notes receivable was $63.7 million and $54.9 million at December 31, 2014 and 2013, respectively. On January 27, 2015, the owners of America’s Square, a 461,000 square foot office complex located in Washington, D.C., gave notice of their intent to prepay, on or about February 24, 2015, a mezzanine loan, which has an outstanding $29.7 million balance of the $30.0 million mezzanine loan that we provided them in April 2011.

(2)	Includes the mortgage debt balance of our Richmond portfolio properties, which have been classified as held-for-sale and is reflected in "Liabilities held-for-sale" on our consolidated balance sheets.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies

	(a) Operating Leases

	Our rental properties are subject to non-cancelable operating leases generating future minimum contractual rent payments due from tenants, which as of December 31, 2014 are as follows (dollars in thousands):



		Future minimum
		contractual
		rent payments
	2015	$	133,834

	2016	127,967

	2017	104,975

	2018	90,376

	2019	76,520

	Thereafter	214,378

		$	748,050


	Our consolidated properties were 87.9% occupied by 582 tenants at December 31, 2014. We did not include square footage that was in development or redevelopment, which totaled 0.2 million square feet at December 31, 2014, in our occupancy calculation.

	We rent office space for our corporate headquarters under a non-cancelable operating lease, which we entered into in 2005. During the fourth quarter of 2011, we entered into a new lease agreement at our corporate headquarters, which expanded our corporate office space by an additional 19,000 square feet. We received an allowance of $1.3 million for tenant improvements to renovate the office space, which was completed prior to us taking occupancy in the fourth quarter of 2012. The lease agreement will expire on January 31, 2021. During the first quarter of 2012, we entered into a lease agreement for approximately 6,000 square feet in Washington, D.C., which served as the location for our Washington, D.C. office. The lease expired in December 2014, at which time, our Washington, D.C. office relocated to our 1211 Connecticut Avenue, NW property in Washington, D.C. and occupied approximately 4,900 square feet.

	During the fourth quarter of 2012, we subleased 5,000 square feet of our corporate office space to one tenant, which commenced in January 2013. During the fourth quarter of 2013, the subtenant amended its lease to include an additional 2,700 square feet, which the subtenant occupied in March 2014. The subtenant’s lease will expire in January 2018 and the lease has a termination option in January 2016.

	Rent expense incurred under the terms of the corporate office leases, net of subleased revenue, was $1.8 million for both the years ended December 31, 2014 and 2013 and $1.4 million for the year ended December 31, 2012.

	Future minimum rental payments under our corporate office leases as of December 31, 2014 are summarized as follows, net of sublease revenue (dollars in thousands):



		Future minimum
		rent payments
	2015	$	1,450

	2016	1,489

	2017	1,529

	2018	1,911

	2019	1,995

	Thereafter	2,224

		$	10,598



	(b) Legal Proceedings

	We are subject to legal proceedings and claims arising in the ordinary course of our business, for which, we carry various forms of insurance to protect the Company. In the opinion of our management and legal counsel, the amount of ultimate liability with respect to these claims will not have a material impact on our financial position, results of operations or cash flows.

	(c) Capital Commitments

	As of December 31, 2014, we had contractual construction in progress obligations, which included amounts accrued at December 31, 2014, of $1.4 million. The amount of contractual construction in progress obligations are primarily related to development activities at Storey Park, which is located in our Washington, D.C. reporting segment. As of December 31, 2014, we had contractual rental property and furniture, fixtures and equipment obligations of $11.8 million outstanding, which included amounts accrued at December 31, 2014. The amount of contractual rental property and furniture, fixtures and equipment obligations at December 31, 2014 included significant tenant improvement costs for a tenant' space at Atlantic Corporate Park, which is located in our Northern Virginia reporting segment. We anticipate meeting our contractual obligations related to our construction activities with cash from our operating activities. In the event cash from our operating activities is not sufficient to meet our contractual obligations, we can access additional capital through our unsecured revolving credit facility.
	We remain liable, solely to the extent of our proportionate ownership percentage, to fund any capital shortfalls or commitments from properties owned through unconsolidated joint ventures.

We have various obligations to certain local municipalities associated with our development projects that will require completion of specified site improvements, such as sewer and road maintenance, grading and other general landscaping work. As of December 31, 2014, we remained liable to those local municipalities for $2.6 million in the event that we do not complete the specified work. We intend to complete the improvements in satisfaction of these obligations.

(d) Insurance

We carry insurance coverage on our properties with policy specifications and insured limits that we believe are adequate given the relative risk of loss, cost of the coverage and standard industry practice. However, certain types of losses (such as from terrorism, earthquakes and floods) may be either uninsurable or not economically insurable. Further, certain of the properties are located in areas that are subject to earthquake activity and floods. Should a property sustain damage as a result of a terrorist act, earthquake or flood, we may incur losses due to insurance deductibles, co-payments on insured losses or uninsured losses. Should an uninsured loss occur, we could lose some or all of our capital investment, cash flow and anticipated profits related to one or more properties.

Equity

Equity	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Equity	Equity

	On May 24, 2013, we completed the public offering of 7.5 million common shares at a public offering price of $14.70 per share, which generated net proceeds of $105.1 million, after deducting the underwriting discount and offering costs. We used a portion of the net proceeds to repay our $10.0 million secured term loan and our $37.5 million secured bridge loan and to pay down $53.0 million of the outstanding balance under our unsecured revolving credit facility. The remaining net proceeds were utilized for general corporate purposes.

	We declared and paid dividends of $0.60 per common share to common shareholders during 2014 and 2013 and $0.80 per common share during 2012. We declared and paid dividends of $1.9375 per share on our Series A Preferred Shares during 2014, 2013 and 2012. On January 27, 2015, we declared a dividend of $0.15 per common share, equating to an annualized dividend of $0.60 per common share. The dividend was paid on February 17, 2015 to common shareholders of record as of February 10, 2015. We also declared a dividend on January 27, 2015 of $0.484375 per share on our Series A Preferred Shares. The dividend was paid on February 17, 2015 to preferred shareholders of record as of February 10, 2015. Dividends on all non-vested share awards are recorded as a reduction of shareholders’ equity. For each dividend paid by us on our common and preferred shares, the Operating Partnership distributes an equivalent distribution on our common and preferred Operating Partnership units, respectively.
	Our unsecured revolving credit facility, unsecured term loan, the Construction Loan, and the Storey Park land loan contain certain restrictions that include, among other things, requirements to maintain specified coverage ratios and other financial covenants, which may limit our ability to make distributions to our common and preferred shareholders. Further, distributions with respect to our common shares are subject to our ability to first satisfy our obligations to pay distributions to the holders of our Series A Preferred Shares.

	For federal income tax purposes, dividends paid to shareholders may be characterized as ordinary income, return of capital or capital gains. The characterization of the dividends declared on our common and preferred shares for 2014, 2013 and 2012 are as follows:



		Common Shares						Preferred Shares
		2014		2013		2012		2014		2013		2012(2)
	Ordinary income(1)	72.42	%	13.53	%	—		100	%	100	%	19.83	%

	Return of capital	27.58	%	86.47	%	100	%	—		—		27.27	%

	Capital gains	—		—		—		—		—		52.9	%



	(1)	The dividends classified above as ordinary income do not represent “qualified dividend income” and, therefore, are not eligible for reduced rates.

	(2)	Figures are estimates.

Noncontrolling_Interests

Noncontrolling Interests	12 Months Ended
	Dec. 31, 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 December 31, 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 $32.5 million. At December 31, 2014 and 2013, we recorded adjustments of $4.7 million and $3.3 million, respectively, to present certain common Operating Partnership units at the greater of their carrying value or redemption value.

	We owned 95.7% of the outstanding common Operating Partnership units at both December 31, 2014 and 2013 and 95.2% at December 31, 2012.

	At December 31, 2014, 2,630,577 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. There were no common Operating Partnership units redeemed for common shares in either 2014 or 2013. During 2012, 322,302 common Operating Partnership units were redeemed for 322,302 common shares. During 2013, 6,718 common Operating Partnership units were redeemed with available cash. There were no common Operating Partnership units redeemed for cash in 2014 or 2012.

	The redeemable noncontrolling interests in the Operating Partnership for the three years ended December 31 are as follows (amounts in thousands):



		Redeemable
		noncontrolling
		interests
	Balance at December 31, 2012	$	34,367

	Net loss	(74		)
	Changes in ownership, net	143

	Distributions to owners	(1,557		)
	Other comprehensive income	342

	Balance at December 31, 2013	33,221

	Net income	199

	Changes in ownership, net	1,465

	Distributions to owners	(1,578		)
	Other comprehensive income	25

	Balance at December 31, 2014	$	33,332


	(b) Noncontrolling Interests in the Consolidated Partnerships

	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 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 (income) loss attributable to noncontrolling interests” in our consolidated statements of operations.

	On August 4, 2011, we formed a joint venture, in which we have a 97% interest, with an affiliate of Perseus Realty, LLC to acquire Storey Park in our Washington, D.C. reporting segment. At the time, the site was leased to Greyhound, which subsequently relocated its operations. Greyhound’s lease expired on August 31, 2013, at which time the property was placed into development. The joint venture anticipates developing a mixed-use project on the 1.6 acre site, which can accommodate up to 712,000 square feet. At December 31, 2014, our total investment in the development project was $55.4 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 October 16, 2014, our 97% own consolidated joint venture repaid a $22.0 million loan that was subject to a 5.0% interest rate floor. The loan encumbered the Storey Park land which is located in Washington, D.C. Simultaneously with the repayment, the joint venture entered into a new $22.0 million loan with a variable-interest rate of LIBOR plus 2.50%.

	In November 2010, we acquired two buildings (Redland II and III) at Redland Corporate Center in a joint venture with Perseus Realty, LLC (“Perseus”) and had a 97% controlling interest in the joint venture. On September 26, 2012, we placed a $68.4 million mortgage loan on Redland II and III. Our joint venture partner received their proportionate share of the proceeds from the mortgage loan. We used our share of the proceeds from the mortgage loan to repay a portion of the outstanding balance under the unsecured revolving credit facility. On November 8, 2013, we acquired the remaining interest in Redland II and III from Perseus for $4.6 million. At December 31, 2013, we eliminated the noncontrolling interests in the consolidated partnership and recorded the excess of cash paid over the noncontrolling interests as “Additional paid-in capital” in our consolidated balance sheets.

Benefit_Plans

Benefit Plans	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Benefit Plans	Benefit Plans

	(a) Share-Based Payments

	We issued share-based payments in the form of stock options and non-vested shares as permitted in our 2003 Equity Compensation Plan (the “2003 Plan”), which was amended in 2005, 2007 and July 2013, and expired in September 2013. We have also issued share-based compensation in the form of stock options and non-vested shares as permitted in our 2009 Equity Compensation Plan (the “2009 Plan”), which was amended in 2010, 2011 and 2013. In 2011, we received shareholder approval to authorize an additional 4.5 million shares for issuance under the 2009 Plan. The compensation plans provide for the issuance of options to purchase common shares, share awards, share appreciation rights, performance units and other equity-based awards. Stock options granted under the plans are non-qualified, and all employees and non-employee trustees are eligible to receive grants. Under the terms of the amendment to the 2009 Plan, every stock option granted by us reduces the awards available for issuance on a one-for-one basis. However, for every restricted award issued, the awards available for issuance are reduced by 3.44 awards. At December 31, 2014, we had 7.4 million share equity awards authorized under the 2009 Plan and, of those awards, 2.8 million common share equity awards remained available for issuance by us.

	We record costs related to our share-based compensation based on the grant-date fair value calculated in accordance with GAAP. We recognize share-based compensation costs on a straight-line basis over the requisite service period for each award and these costs are recorded within “General and administrative expense” or “Property operating expense” in our consolidated statements of operations based on the employee’s job function.

	Stock Options Summary

	As of December 31, 2014, 2.2 million stock options have been awarded of which 1.1 million stock options remained outstanding. During the first quarter of 2014, we issued 135,250 stock options to our non-officer employees. The stock options vest 25% on the first anniversary of the date of grant and 6.25% in each subsequent calendar quarter. The awards described above have a ten-year contractual life. We recognized $0.5 million of compensation expense associated with stock option awards for both years ended December 31, 2014 and 2013, and $0.6 million for the year ended December 31, 2012.

	A summary of our stock option activity for the three years ended December 31 is presented below:


		Options			Weighted				Weighted Average		Aggregate
					Average				Remaining		Intrinsic
					Exercise Price				Contractual Term		Value
	Outstanding at December 31, 2011	887,168			$	16.76			4.4 years		$	293,930

	Granted	627,500			14.7

	Exercised	(7,326	)		9.63

	Forfeited	(123,336	)		16.25

	Outstanding at December 31, 2012	1,384,006			15.91				5.9 years		$	174,763

	Granted	124,250			12.73

	Exercised	(14,733	)		11.05

	Expired	(298,469	)		15

	Forfeited	(105,762	)		16.17

	Outstanding at December 31, 2013	1,089,292			15.83				6.6 years		$	109,151

	Granted	135,250			11.61

	Exercised	(17,171	)		10.1

	Expired	(57,500	)		19.08

	Forfeited	(98,512	)		14.49

	Outstanding at December 31, 2014	1,051,359			$	15.33			6.3 years		$	181,352

	Exercisable at December 31:
	2014	552,620			$	16.49			5.1 years		$	102,039

	2013	521,723			17.25				4.9 years		109,151

	2012	693,854			17.01				2.9 years		162,593

	Options expected to vest, subsequent to December 31, 2014	485,733			$	14.11			7.5 years		$	71,358


	The following table summarizes information about our stock options at December 31, 2014:


					Options Outstanding									Options Exercisable
	Year	Range of			Options			Weighted Average		Weighted				Options			Weighted
	Issued	Exercise Prices						Remaining		Average							Average
			Contractual Life					Exercise Price			Exercise Price
2005	$22.42 - 22.54			59,000			0.0 years			$	22.44				59,000			$	22.44

2006	26.6			17,350			1.0 year		26.6				17,350			26.6

2007	29.11 - 29.24			31,500			2.0 years		29.13				31,500			29.13

2008	17.29			39,000			3.0 years		17.29				39,000			17.29

2009	9.3			33,346			4.0 years		9.3				33,346			9.3

2010	12.57			42,705			5.0 years		12.57				42,705			12.57

2011	15.17 - 17.12			77,188			6.1 years		16.36				72,664			16.37

2012	13.54 - 15.00			566,533			7.0 years		14.83				219,678			14.68

2013	12.73			78,987			8.0 years		12.73				37,377			12.73

2014	11.61			105,750			9.0 years		11.61				—			—

				1,051,359			6.3 years		15.33				552,620			16.49


As of December 31, 2014, we had $1.4 million of unrecognized compensation cost, net of estimated forfeitures, related to stock option awards. We anticipate this cost will be recognized over a weighted-average period of approximately 4.2 years. We calculate the grant date fair value of option awards using a Black-Scholes option-pricing model. Expected volatility is based on an assessment of our realized volatility over the preceding period that is equivalent to the award’s expected life, which in our opinion, gives an accurate indication of future volatility. The expected term represents the period of time the options are anticipated to remain outstanding as well as our historical experience for groupings of employees that have similar behavior and are considered separately for valuation purposes. The risk-free rate is based on the U.S. Treasury rate at the time of grant for instruments of similar term.
The weighted average assumptions used in the fair value determination of stock options granted to employees for the years ended December 31 are summarized as follows:



	2014			2013			2012
Risk-free interest rate	1.72	%		0.76	%		1.28	%
Expected volatility	39	%		49.7	%		45.6	%
Expected dividend yield	4.66	%		4.92	%		5.71	%
Weighted average expected life of options	5.0 years			5.0 years			6.6 years


The weighted average grant date fair value of the stock options issued in 2014, 2013 and 2012 was $2.67, $3.61 and $3.27, respectively.

Option Exercises

We received $174 thousand, $163 thousand and $71 thousand from the exercise of stock options during 2014, 2013 and 2012, respectively. Shares issued as a result of stock option exercises are provided by the issuance of new shares. The total intrinsic value of options exercised was $43 thousand in both 2014 and 2013, and $25 thousand in 2012.

Non-Vested Share Awards

We issue non-vested common share awards that either vest over a specific time period that is identified at the time of issuance or vest upon the achievement of specific performance goals that are identified at the time of issuance. We issue new common shares, subject to restrictions, upon each grant of non-vested common share awards. In February 2014, we granted a total of 103,075 non-vested common shares in two separate awards to our officers. The first award of 91,466 non-vested common shares, which was granted to all of our officers, will vest ratably on the date of issuance over a three-year term. The second award of 11,609 non-vested common shares was granted to our Chief Executive Officer and vested on February 19, 2015, one year after issuance. In addition, we granted a total of 31,808 non-vested common shares in two separate awards to two new executive officers in connection with each of their respective appointments in 2014. The first award of 15,128 non-vested common shares was granted to our new Chief Operating Officer in June 2014 and the second award of 16,680 non-vested common shares was granted to our new General Counsel in October 2014. Both common share awards will vest ratably on an annual basis over a three-year period from the date of grant.

We recognized $2.8 million, $3.5 million and $2.6 million of compensation expense associated with our non-vested common share awards in 2014, 2013 and 2012, respectively. Compensation expense associated with our non-vested common shares during 2013 and 2012 included $1.2 million and $0.7 million, respectively, of expense related to the accelerated vesting of the restricted shares associated with the departure of our former officers. Dividends on all non-vested common share awards are recorded as a reduction of equity. We apply the two-class method for determining EPS as our outstanding non-vested common shares with non-forfeitable dividend rights are considered participating securities. Our excess of dividends over earnings related to participating securities are shown as a reduction in net income or loss attributable to common shareholders in our computation of EPS.

Independent members of our Board of Trustees received annual grants of restricted common shares as a component of compensation for serving on our Board of Trustees. In May 2014, we granted 29,792 non-vested common shares to our non-employee trustees, all of which will vest on the earlier of the first anniversary of the grant date or the date of our 2015 annual meetings of our shareholders, subject to continued service by the trustee until that date. We recognized $0.4 million of compensation expense associated with trustee restricted share awards for both the years ended December 31, 2014 and 2013, and $0.3 million for the year ended December 2012.

A summary of our non-vested common share awards at December 31, 2014 is as follows:



	Non-vested			Weighted Average
	Shares			Grant Date
				Fair Value
Non-vested at December 31, 2011	748,968			$	12.67

Granted	355,612			13.87

Vested	(309,605	)		13.52

Expired	(61,944	)		11.36

Forfeited	(59,203	)		15.03

Non-vested at December 31, 2012	673,828			12.83

Granted	313,086			12.14

Vested	(297,778	)		12.89

Expired	(45,049	)		11.42

Forfeited	(6,425	)		14.01

Non-vested at December 31, 2013	637,662			13.33

Granted	164,675			12.84

Vested	(137,924	)		14.21

Expired	(29,514	)		10.21

Forfeited	(11,478	)		13.04

Non-vested at December 31, 2014	623,421			$	13.16


As of December 31, 2014, we had $3.9 million of unrecognized compensation cost related to non-vested common shares. We anticipate this cost will be recognized over a weighted-average period of 2.2 years.

We value our non-vested time-based awards issued in 2014, 2013 and 2012 at the grant date fair value, which is the market price of our common shares. For the non-vested performance-based share awards issued in 2013, we used a Monte Carlo Simulation (risk-neutral approach) to determine the number of shares that may be issued pursuant to the award. The risk-free interest rate assumptions used in the Monte Carlo Simulation were determined based on the zero coupon risk-free rate for the time frame of 0.25 years to 3.0 years, which ranged from 0.11% to 0.4%, respectively. The volatility used for our common share price in the Monte Carlo Simulation varied between 24.31% and 29.11%. We did not issue any non-vested performance-based awards in 2014 or 2012.

The weighted average grant date fair value of the shares issued in 2014, 2013 and 2012 were $12.84, $12.14 and $13.87, respectively. The total fair value of shares vested were $2.0 million, $3.8 million and $4.2 million at December 31, 2014, 2013 and 2012, respectively. We issue new shares, subject to restrictions, upon each grant of non-vested common share awards.

(b) 401(k) Plan

We have a 401(k) defined contribution plan covering all employees in accordance with the Internal Revenue Code. The maximum employer or employee contribution cannot exceed the IRS limits for the plan year. In 2014, we amended the eligibility requirements of the plan, allowing employees to contribute after 60 days of consecutive service. Employee contributions vest immediately. Employer contributions begin one year after the employee's start of service and vest ratably over four years. For the three years ended December 31, 2014, 2013 and 2012, we matched up to 6% of each employee’s contributions. We pay for administrative expenses and matching contributions with available cash. Our plan does not allow for us to make additional discretionary contributions. Our contributions were $0.6 million for both the years ended December 31, 2014 and 2013, and $0.5 million for the year ended December 31, 2012. The employer match payable to the 401(k) plan was fully funded as of December 31, 2014.

(c) Employee Share Purchase Plan

In 2009, our common shareholders approved the First Potomac Realty Trust 2009 Employee Share Purchase Plan (“the Plan”). The Plan allows participating employees to acquire our common shares, at a discounted price, through payroll deductions or cash contributions. Under the Plan, a total of 200,000 common shares may be issued and the offering periods of the Plan will not exceed five years. Each offering period will commence on the first day of each calendar quarter (offering date) and will end on the last business day of the calendar quarter (purchase date) in which the offering period commenced. The purchase price at which common shares will be sold in any offering period will be the lower of: a) 85 percent of the fair value of common shares on the offering date or b) 85 percent of the fair value of the common shares on the purchase date. The first offering period began during the fourth quarter of 2009. We issued common shares of 8,950, 11,007 and 14,470 under the Plan during the years ended December 31, 2014, 2013 and 2012, respectively, which resulted in compensation expense totaling $20 thousand, $26 thousand and $42 thousand, respectively.

Segment_Information

Segment Information	12 Months Ended
	Dec. 31, 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 for our four reporting segments for the three years ended December 31 are as follows (dollars in thousands):



		2014
		Washington, D.C.				Maryland				Northern Virginia				Southern Virginia				Consolidated
	Number of buildings(1)	6				38				49				38				131

	Square feet(1)	917,008				1,999,332				3,021,509				2,852,298				8,790,147

	Total revenues	$	33,959			$	45,767			$	53,645			$	28,281			$	161,652

	Property operating expense	(9,683		)		(11,482		)		(13,352		)		(8,735		)		(43,252		)
	Real estate taxes and insurance	(5,583		)		(3,907		)		(5,592		)		(2,278		)		(17,360		)
	Total property operating income	$	18,693			$	30,378			$	34,701			$	17,268			101,040

	Depreciation and amortization expense																	(61,796		)

	General and administrative																	(21,156		)

	Acquisition costs																	(2,681		)

	Impairment of rental property																	(3,956		)

	Other income																	4,108

	Income from discontinued operations																	1,484

	Net income																	$	17,043

	Total assets(2)(3)	$	505,842			$	360,470			$	439,833			$	228,306			$	1,618,460

	Capital expenditures(4)	$	23,422			$	10,185			$	7,816			$	8,436			$	50,789




		2013
		Washington, D.C.				Maryland				Northern Virginia				Southern Virginia				Consolidated
	Number of buildings(1)(5)	4				53				51				38				146

	Square feet(1)(5)	522,605				2,638,988				3,086,057				2,852,471				9,100,121

	Total revenues	$	28,208			$	41,735			$	51,787			$	27,085			$	148,815

	Property operating expense	(6,693		)		(10,579		)		(12,601		)		(8,407		)		(38,280		)
	Real estate taxes and insurance	(4,792		)		(3,436		)		(5,679		)		(2,167		)		(16,074		)
	Total property operating income	$	16,723			$	27,720			$	33,507			$	16,511			94,461

	Depreciation and amortization expense																	(54,567		)

	General and administrative																	(21,979		)

	Acquisition costs																	(602		)

	Contingent consideration related to acquisition of property																	213

	Other expenses																	(28,287		)

Income from discontinued operations																	21,742

Net income																	10,981

Total assets(2)(3)	$	344,739			$	430,498			$	423,839			$	230,175			$	1,502,460

Capital expenditures(4)	$	26,910			$	16,216			$	13,685			$	10,106			$	68,002




	2012
	Washington, D.C.				Maryland				Northern Virginia				Southern Virginia				Consolidated
Number of buildings(6)	3				62				56				57				178

Square feet(6)	531,714				3,781,379				3,654,527				5,483,781				13,451,401

Total revenues	$	27,718			$	41,726			$	47,207			$	26,311			$	142,962

Property operating expense	(5,298		)		(9,862		)		(11,519		)		(7,643		)		(34,322		)
Real estate taxes and insurance	(3,876		)		(3,170		)		(5,020		)		(2,119		)		(14,185		)
Total property operating income	$	18,544			$	28,694			$	30,668			$	16,549			94,455

Depreciation and amortization expense																	(51,457		)

General and administrative																	(23,568		)

Acquisition costs																	(49		)

Contingent consideration related to acquisition of property																	(152		)

Impairment of rental property																	(2,444		)
Other expenses																	(45,251		)

Benefit from income taxes																	4,142

Income from discontinued operations																	15,943

Net loss																	$	(8,381	)

Total assets(2)(3)	$	321,875			$	493,267			$	462,667			$	364,514			$	1,717,748

Capital expenditures(4)	$	12,023			$	23,163			$	20,959			$	12,897			$	70,486



(1)	Excludes Storey Park from our Washington, D.C. reporting segment, which was placed in development in the third quarter of 2013.

(2)	Total assets include our investment in properties that are owned through joint ventures that are not consolidated within our consolidated financial statements. For more information on our unconsolidated investments, including location within our reportable segments, see note 6, Investment in Affiliates.

(3)	Corporate assets not allocated to any of our reportable segments totaled $84,009, $73,209 and $75,425 at December 31, 2014, 2013 and 2012, respectively.

(4)	Capital expenditures for corporate assets not allocated to any of our reportable segments totaled $930, $1,085 and $1,444 at December 31, 2014, 2013 and 2012, respectively.

(5)	Includes occupied space at 440 First Street, NW in our Washington, D.C. reporting segment, which was substantially completed in the third quarter of 2013. In 2014, the property was placed in service.

(6)	Our Washington, D.C. reporting segment excludes 440 First Street, NW, which was in redevelopment during 2012.

Quarterly_Financial_Informatio

Quarterly Financial Information (unaudited)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information (unaudited)	Quarterly Financial Information (unaudited)



		2014(1)
		First			Second			Third			Fourth
	(amounts in thousands, except per share amounts)	Quarter			Quarter			Quarter			Quarter
	Revenues	$	39,363		$	39,307		$	40,055		$	42,928

	Operating expenses	35,744			39,579			36,283			38,595

	Operating income (loss)	3,619			(272		)	3,772			4,333

	(Loss) income from continuing operations	(586		)	16,796			(248		)	(402		)

	(Loss) income from discontinued operations	(857		)	1,538			297			505

	Less: Net loss (income) attributable to noncontrolling interests	195			(652		)	131			128

	Net (loss) income attributable to First Potomac Realty Trust	(1,248		)	17,682			180			231

	Less: Dividends on preferred shares	(3,100		)	(3,100		)	(3,100		)	(3,100		)
	Net (loss) income attributable to common shareholders	$	(4,348	)	$	14,582		$	(2,920	)	$	(2,869	)

	Basic and diluted earnings per common share:
	(Loss) income from continuing operations	$	(0.07	)	$	0.22		$	(0.05	)	$	(0.06	)

	(Loss) income from discontinued operations	(0.01		)	0.03			—			0.01

	Net (loss) income	$	(0.08	)	$	0.25		$	(0.05	)	$	(0.05	)




		2013(1)
		First			Second			Third			Fourth
	(amounts in thousands, except per share amounts)	Quarter			Quarter			Quarter			Quarter
	Revenues	$	37,179		$	36,915		$	37,206		$	37,517

	Operating expenses	32,508			31,221			33,663			33,899

	Operating income	4,671			5,694			3,543			3,618

	Loss from continuing operations	(3,638		)	(2,192		)	(2,509		)	(2,421		)
	Income (loss) from discontinued operations	5,601			16,668			792			(1,320		)

	Less: Net loss (income) attributable to noncontrolling interests	59			(466		)	211			288

	Net income (loss) attributable to First Potomac Realty Trust	2,022			14,010			(1,506		)	(3,453		)

	Less: Dividends on preferred shares	(3,100		)	(3,100		)	(3,100		)	(3,100		)
	Net (loss) income attributable to common shareholders	$	(1,078	)	$	10,910		$	(4,606	)	$	(6,553	)

	Basic and diluted earnings per common share:
	Loss from continuing operations	$	(0.13	)	$	(0.10	)	$	(0.09	)	$	(0.09	)
	Income (loss) from discontinued operations	0.11			0.3			0.01			(0.02		)

	Net (loss) income	$	(0.02	)	$	0.2		$	(0.08	)	$	(0.11	)



	(1)	These figures are rounded to the nearest thousand, which may impact cross-footing in reconciling to full year totals.

	We did not sell any common shares in 2014 and sold 7.5 million common shares in 2013. The sum of the basic and diluted earnings per common share for the four quarters in the periods presented differs from the annual earnings per common share calculation due to the required method of computing the weighted average number of common shares in the respective periods.

Schedule_III_Real_Estate_and_A

Schedule III - Real Estate and Accumulated Depreciation	12 Months Ended
	Dec. 31, 2014
SEC Schedule III, Real Estate and Accumulated Depreciation Disclosure [Abstract]
Schedule III - Real Estate and Accumulated Depreciation	SCHEDULE III
	FIRST POTOMAC REALTY TRUST
	REAL ESTATE AND ACCUMULATED DEPRECIATION
	December 31, 2014
	(Amounts in thousands)


	Property	Location(1)		Date Acquired		Property Type(2)		Encumbrances at
								December 31, 2014(3)
	Maryland
	Rumsey Center	Columbia		Oct-02		BP		$	8,160

	Snowden Center	Columbia		Oct-02		BP		11,081

	Metro Park North	Rockville		Dec-04		Office		—

	Gateway 270 West	Clarksburg		Jul-06		BP		—

	Indian Creek Court	Beltsville		Aug-06		BP		—

	Ammendale Commerce Center	Beltsville		Mar-07		BP		—

	Annapolis Business Center	Annapolis		Jun-07		Office		—

	Cloverleaf Center	Germantown		Oct-09		Office		—

	Redland Corporate Center Buildings II & III	Rockville		Nov-10		Office		65,816

	TenThreeTwenty	Columbia		Feb-11		Office		—

	Hillside I and II	Columbia		Nov-11		Office		12,949

	540 Gaither Road (Redland I)	Rockville		Oct-13		Office		—

	Total Maryland							98,006

	Washington, D.C.
	500 First Street, NW	Capitol Hill		Jun-10		Office		—

	440 First Street, NW	Capitol Hill		Dec-10		Office		32,216

	1211 Connecticut Ave, NW	CBD		Dec-10		Office		29,691

	840 First Street, NE	NoMA		Mar-11		Office		36,539

	Storey Park	NoMA		Aug-11		Office		22,000

	1401 K Street, NW	East End		Apr-14		Office		36,861

	11 Dupont Circle, NW	CBD		Sep-14		Office		—

	Total Washington, D.C.							157,307

	Northern Virginia
	Plaza 500	Alexandria		Dec-97		I		30,277

	Van Buren Office Park	Herndon		Dec-97		Office		6,790

	Newington Business Park Center	Lorton		Dec-99		I		—

	Herndon Corporate Center	Herndon		Apr-04		Office		—

	Windsor at Battlefield	Manassas		Dec-04		Office		—

Reston Business Campus	Reston		Mar-05		Office		—

Enterprise Center	Chantilly		Apr-05		Office		—

Gateway Centre Manassas	Manassas		Jul-05		BP		432

403/405 Glenn Drive	Sterling		Oct-05		BP		—

Linden Business Center	Manassas		Oct-05		BP		—

Prosperity Business Center	Merrifield		Nov-05		BP		—

Sterling Park Business Center	Sterling		Feb-06		BP		—

Davis Drive	Sterling		Aug-06		BP		—

Three Flint Hill	Oakton		Dec-09		Office		—

Atlantic Corporate Park	Sterling		Apr-10		Office		—

Cedar Hill	Tyson’s Corner		Nov-10		Office		—

One Fair Oaks	Fairfax		Feb-11		Office		—

1775 Wiehle Avenue	Reston		Apr-11		Office		—

Total Northern Virginia							37,499

Southern Virginia


Property	Location(1)		Date Acquired		Property Type(2)		Encumbrances at
							December 31, 2014(3)
Crossways Commerce Center	Chesapeake		Dec-99		BP		—

Greenbrier Technology Center II	Chesapeake		Oct-02		BP		4,452

Norfolk Business Center	Norfolk		Oct-02		BP		4,183

Crossways II	Chesapeake		Oct-04		BP		—

Norfolk Commerce Park II	Norfolk		Oct-04		BP		—

1434 Crossways Boulevard	Chesapeake		Aug-05		BP		—

Crossways I	Chesapeake		Feb-06		BP		—

Crossways Commerce Center IV	Chesapeake		May-06		BP		—

Gateway II	Norfolk		Nov-06		BP		—

Greenbrier Circle Corporate Center	Chesapeake		Jan-07		BP		—

Greenbrier Technology Center I	Chesapeake		Jan-07		BP		—

Battlefield Corporate Center	Chesapeake		Oct-10		BP		3,692

Greenbrier Towers	Chesapeake		Jul-11		Office		—

Total Southern Virginia							12,327

Land held for future development							—

Other							—

Total Consolidated Portfolio							$	305,139



Initial Costs								Gross Amount at End of Year
Land				Building and				Since Acquisition(4)				Land		Building and		Total		Accumulated
				Improvements										Improvements				Depreciation
$	2,675			$	10,196			$	3,705			$	2,675	$	13,901	$	16,576	$	5,502

3,404				12,824				4,238				3,404		17,062		20,466		6,165

9,220				32,056				2,997				9,220		35,053		44,273		8,671

18,302				20,562				5,708				18,302		26,270		44,572		5,850

5,673				17,168				12,862				5,673		30,030		35,703		7,563

2,398				7,659				6,116				2,398		13,775		16,173		5,805

6,101				12,602				469				6,101		13,071		19,172		2,469

7,097				14,211				433				7,097		14,644		21,741		2,322

17,272				63,480				13,869				17,272		77,349		94,621		12,014

2,041				5,327				11,894				2,041		17,221		19,262		2,209

3,302				10,926				968				3,302		11,894		15,196		827

6,458				19,831				94				6,457		19,926		26,383		1,271

83,943				226,842				63,353				83,942		290,196		374,138		60,668

25,806				33,883				410				25,806		34,293		60,099		4,918

—				15,300				45,601				9,118		51,783		60,901		913

27,077				17,520				9,734				27,077		27,254		54,331		2,286

16,846				60,905				11,020				16,846		71,925		88,771		7,715

43,672				4,194				7,578				—		55,444		55,444		—

29,506				23,269				(105		)		29,506		23,165		52,671		987

15,744				64,832				3,381				15,744		68,214		83,958		588

158,651				219,903				77,619				124,097		332,078		456,175		17,407

6,265				35,433				6,499				6,268		41,929		48,197		17,897

3,592				7,652				5,446				3,607		13,083		16,690		5,084

3,135				10,354				4,094				3,135		14,448		17,583		5,798

4,082				14,651				1,666				4,082		16,317		20,399		4,670

3,228				11,696				3,444				3,228		15,140		18,368		5,384

1,996				8,778				3,501				1,996		12,279		14,275		2,961

3,727				27,274				4,221				3,728		31,494		35,222		8,992

3,015				6,734				1,524				3,015		8,258		11,273		2,406

3,940				12,547				4,371				3,940		16,918		20,858		4,716

4,829				10,978				1,233				4,829		12,211		17,040		3,258

5,881				3,495				667				5,881		4,162		10,043		1,118

19,897				10,750				20,600				15,614		35,633		51,247		6,728

1,614				3,611				3,402				1,646		6,981		8,627		1,610

—				13,653				24,459				4,181		33,931		38,112		5,092

5,895				11,655				13,495				5,895		25,150		31,045		3,451

5,306				13,554				3,173				5,306		16,727		22,033		2,688

5,688				43,176				6,332				5,688		49,508		55,196		7,098

3,542				30,575				—				3,542		30,575		34,117		687

85,632				276,566				108,127				85,581		384,744		470,325		89,638

5,160				23,660				13,517				5,160		37,177		42,337		14,030

1,365				5,119				1,042				1,365		6,161		7,526		2,195

1,323				4,967				952				1,324		5,918		7,242		2,186

1,036				6,254				1,165				1,036		7,419		8,455		2,182

1,221				8,693				4,364				1,221		13,057		14,278		4,123

4,447				24,739				3,211				4,815		27,582		32,397		6,457

2,657				11,597				2,810				2,646		14,418		17,064		3,647



Initial Costs								Gross Amount at End of Year
Land				Building and				Since Acquisition(4)				Land		Building and		Total		Accumulated
				Improvements										Improvements				Depreciation
1,292				3,899				700				1,292		4,599		5,891		1,390

1,320				2,293				818				1,320		3,111		4,431		801

4,164				18,984				4,101				4,164		23,085		27,249		5,375

2,024				7,960				1,703				2,024		9,663		11,687		2,614

1,860				6,071				786				1,881		6,836		8,717		926

2,997				9,173				3,849				2,997		13,022		16,019		1,775

30,866				133,409				39,018				31,245		172,048		203,293		47,701

343				—				371				349		—		349		—

—				—				92				—		92		92		85

$	359,435			$	856,720			$	288,580			$	325,214	$	1,179,158	$	1,504,372	$	215,499



(1)	CBDNntral Business District; NoMA=rth of Massachusetts Avenue

(2)	I=dustrial; BP=siness Park

(3)	Includes the unamortized fair value adjustments recorded at acquisition upon the assumption of mortgage loans.

(4)	We placed Storey Park into development on September 1, 2013. At December 31, 2014, the land and building assets associated with Storey Park are included in construction in progress, which is reflected in Building and Improvements in the above table.

Depreciation of rental property is computed on a straight-line basis over the estimated useful lives of the assets. The estimated lives of our assets range from 5 to 39 years or to the term of the underlying lease. The tax basis of our rental property assets was $1,576 million and $1,667 million at December 31, 2014 and 2013, respectively.
















(a) Reconciliation of Real Estate(1)

The following table reconciles the rental property investments for the years ended December 31 (amounts in thousands):



	2014				2013				2012
Beginning balance	$	1,330,180			$	1,605,722			$	1,553,802

Acquisitions of rental property(2)	170,823				26,289				—

Capital expenditures(3)	49,860				66,808				69,042

Impairments	(3,956		)		(4,069		)		(3,401		)
Dispositions of rental property	(30,916		)		(290,777		)		(10,963		)
Assets held-for-sale	(643		)		(55,767		)		(1,183		)
Other(4)	(10,976		)		(18,026		)		(1,575		)
Ending balance	$	1,504,372			$	1,330,180			$	1,605,722


(b) Reconciliation of Accumulated Depreciation(1)

The following table reconciles the accumulated depreciation on the rental property investments for the years ended December 31 (amounts in thousands):



	2014				2013				2012
Beginning balance	$	185,725			$	215,154			$	175,083

Depreciation of rental property	47,625				48,638				49,333

Assets held-for-sale	(1,631		)		(13,470		)		(2,014		)
Dispositions of rental property	(5,712		)		(54,377		)		(2,173		)
Other(4)	(10,508		)		(10,220		)		(5,075		)
Ending balance	$	215,499			$	185,725			$	215,154



(1)	Effective as of February 9, 2015, we entered into a binding contract to sell our Richmond, Virginia portfolio for sale, which is located in our Southern Virginia reporting segment. The Richmond Portfolio consists of Chesterfield Business Center, Hanover Business Center, Park Central, Virginia Technology Center and a three-acre parcel of undeveloped land. We anticipate closing the sale in the first half of 2015. However, we can provide no assurances regarding the timing or pricing of the sale of the Richmond Portfolio, or that the sale will occur at all. With the sale of our Richmond Portfolio, we will no longer own any properties in the Richmond, Virginia area and will have strategically exited the Richmond market. As such, in accordance with ASU 2014-08, our Richmond Portfolio was classified as held-for-sale at December 31, 2014 and the assets and liabilities of the Richmond Portfolio are reflected within "Assets held-for-sale" and "Liabilities held-for-sale," respectively, in our consolidated balance sheets for each of the periods presented. The rental property and applicable accumulated depreciation related to the Richmond Portfolio have been removed from all years presented in this table.

(2)	For more information on our acquisitions, including the assumption of liabilities and other non-cash items, see the supplemental disclosure of cash flow information accompanying our consolidated statements of cash flows.

(3)	Represents cash paid for capital expenditures.

(4)	Includes accrued increases to rental property investments, fully depreciated assets that were written-off during the year and other immaterial transactions.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2014

Accounting Policies [Abstract]

Principles of Consolidation

(a) Principles of Consolidation

Use of Estimates

(b) Use of Estimates

Revenue Recognition and Accounts Receivable

Cash and Cash Equivalents

(d) Cash and Cash Equivalents

We consider all highly liquid investments with a maturity of 90 days or less at the date of purchase to be cash equivalents.

Escrows and Reserves

(e) Escrows and Reserves

Deferred Costs

(f) Deferred Costs

The following table sets forth scheduled future amortization for deferred financing and leasing costs at December 31, 2014 (amounts in thousands):

Deferred

Financing(1)

Leasing(1)(2)

Lease Incentive

2015

1,905

5,446

637

2016

1,533

4,977

637

2017

1,153

4,181

552

2018

836

3,593

518

2019

308

2,828

443

Thereafter

425

7,849

1,627

6,160

28,874

4,414

(1)

Includes amounts from properties that were classified as held-for-sale at December 31, 2014.

(2)

Rental Property

(g) Rental Property

Buildings

39 years

Building improvements

5 to 20 years

Furniture, fixtures and equipment

5 to 15 years

Tenant improvements

Shorter of the useful life of the asset or the term of the related lease

Purchase Accounting

(h) Purchase Accounting

•

the fair value of intangible tenant or customer relationships.

Investment in Affiliates

(i) Investment in Affiliates

Sales of Real Estate

(j) Sales of Rental Property

Intangible Assets

(k) Intangible Assets

Derivative Instruments

(l) Derivative Instruments

•

available interest rate hedging may not correspond directly with the interest rate risk for which we seek protection;

•

the duration of the hedge may not match the duration of the related liability;

•

the party owing money in the hedging transaction may default on its obligation to pay; and

•

the credit quality of the party owing money on the hedge may be downgraded to such an extent that it impairs our ability to sell or assign its side of the hedging transaction.

Income Taxes

(m) Income Taxes

Share-Based Payments

(n) Share-Based Payments

Notes Receivable

(o) Notes Receivable

Reclassifications

(p) Reclassifications

Application of New Accounting Standards

(q) Application of New Accounting Standards

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Scheduled Future Amortization for Deferred Financing and Leasing Costs	The following table sets forth scheduled future amortization for deferred financing and leasing costs at December 31, 2014 (amounts in thousands):



		Deferred			Deferred		Deferred
		Financing(1)			Leasing(1)(2)		Lease Incentive
	2015	$	1,905		$	5,446	$	637

	2016	1,533			4,977		637

	2017	1,153			4,181		552

	2018	836			3,593		518

	2019	308			2,828		443

	Thereafter	425			7,849		1,627

		$	6,160		$	28,874	$	4,414



	(1)	Includes amounts from properties that were classified as held-for-sale at December 31, 2014.

	(2)	Excludes the amortization of $5.6 million of leasing costs that have yet to be placed in-service as the associated tenants have not moved into their related spaces and, therefore, the period over which the leasing costs will be amortized has yet to be determined.
Estimated Useful Lives of Company's Assets, by Class	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
		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)	12 Months Ended
	Dec. 31, 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):



		2014				2013			2012
	Numerator for basic and diluted earnings per common share:
	Income (loss) from continuing operations	$	15,559			$	(10,761	)	$	(24,324	)

	Income from discontinued operations	1,484				21,742			15,943

	Net income (loss)	17,043				10,981			(8,381		)

	Less: Net (income) loss from continuing operations attributable to noncontrolling interests	(135		)		1,047			1,780

	Less: Net income from discontinued operations attributable to noncontrolling interests	(64		)		(954		)	(794		)
	Net income (loss) attributable to First Potomac Realty Trust	16,844				11,074			(7,395		)

	Less: Dividends on preferred shares	(12,400		)		(12,400		)	(11,964		)
	Net income (loss) attributable to common shareholders	4,444				(1,326		)	(19,359		)

	Less: Allocation to participating securities	(314		)		(388		)	(620		)
	Net income (loss) attributable to common shareholders	$	4,130			$	(1,714	)	$	(19,979	)

	Denominator for basic and diluted earnings per common share:
	Weighted average common shares outstanding – basic	58,150				55,034			50,120

	Weighted average common shares outstanding – diluted	58,220				55,034			50,120

	Basic and diluted earnings per common share:
	Income (loss) from continuing operations	$	0.05			$	(0.41	)	$	(0.70	)

	Income from discontinued operations	0.02				0.38			0.3

	Net income (loss)	$	0.07			$	(0.03	)	$	(0.40	)

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):



		2014			2013			2012
	Stock option awards	1,122			1,369			1,462

	Non-vested share awards	398			471			553

	Series A Preferred Shares(1)	12,616			12,076			12,162

		14,136			13,916			14,177



	(1)	In March 2012, we issued an additional 1.8 million Series A Preferred Shares, which 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)	12 Months Ended
	Dec. 31, 2014
Text Block [Abstract]
Summary of Rental Property	Rental property consists of the following at December 31 (amounts in thousands):



		2014 (1)			2013 (1)
	Land and land improvements	$	325,214		$	287,015

	Buildings and improvements	949,683			807,198

	Construction in progress	69,181			93,174

	Tenant improvements	159,867			138,543

	Furniture, fixtures and equipment	427			4,250

		1,504,372			1,330,180

	Less: accumulated depreciation	(215,499		)	(185,725		)
		$	1,288,873		$	1,144,455



	(1)	Excludes rental property related to properties held-for-sale totaling $57.7 million and $102.4 million at December 31, 2014 and 2013, respectively. For more information, see note 10, Dispositions.

Acquisitions_Tables

Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2014
Business Combinations [Abstract]
Schedule of Business Acquisitions, by Acquisition	During 2014 and 2013, we acquired the following properties (dollars in thousands):


	Property	Reporting Segment	Acquisition Date	Property Type	Square Feet	Contractual Purchase Price
	11 Dupont Circle, NW(1)	Washington, DC	September 24, 2014	Office	153,018	$89,000
	1775 Wiehle Avenue(2)	Northern Virginia	June 25, 2014	Office	130,048	$41,000
	1401 K Street, NW(3)	Washington, DC	April 8, 2014	Office	118,292	$58,000
	540 Gaither Road(4)	Maryland	October 1, 2013	Office	133,895	$30,000

	(1) The acquisition was funded with a draw under our unsecured revolving credit facility.
	(2) The acquisition was funded with the net proceeds from the sale of Corporate Campus at Ashburn Center and available cash.
	(3) The acquisition was funded with the assumption of a $37.3 million mortgage loan and a draw under our unsecured revolving credit facility.
	(4) The acquisition was funded with $28.2 million of proceeds from the sale of our industrial portfolio in June 2013 that was previously placed with a qualified intermediary to facilitate a tax-free exchange, as well as available cash.
Fair Value of Acquired Net Assets	The fair values of the net assets acquired in 2014 are as follows (amounts in thousands):



		2014				2013
	Land	$	48,792			$	6,458

	Acquired tenant improvements	10,857				1,669

	Building and improvements	111,173				18,162

	In-place leases	12,540				2,886

	Acquired leasing commissions	4,681				580

	Legal leasing fees	360				2

	Above-market leases acquired	2,397				243

	Total assets acquired	190,800				30,000

	Below-market leases assumed	(2,800		)		—

	Debt assumed	(37,269		)		—

	Net assets acquired	$	150,731			$	30,000

Pro Forma Financial Information	The unaudited pro forma financial information set forth below presents results for the twelve months ended December 31, 2014 and 2013 as if all of our 2014 and 2013 acquisitions (1401 K Street, NW, 1775 Wiehle Avenue, 11 Dupont Circle, NW and 540 Gaither Road), and related financings, 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 (amounts in thousands, except per share amounts):



		2014				2013
	Pro forma total revenues	$	171,686			$	170,800

	Pro forma net income	$	19,461			$	5,572

	Pro forma net income (loss) per share – basic and diluted	$	0.12			$	(0.12	)

Investment_in_Affiliates_Table

Investment in Affiliates (Tables)	12 Months Ended
	Dec. 31, 2014
Equity Method Investments and Joint Ventures [Abstract]
Components of Investments in Affiliates	Our investment in affiliates consisted of the following at December 31 (dollars in thousands):



				2014
		Reporting Segment		Ownership			Company			Debt			Recourse
				Interest			Investment						Debt(1)
	Prosperity Metro Plaza	Northern Virginia		51	%		$	24,651		$	50,000	(2)	$	—

	1750 H Street, NW	Washington, D.C.		50	%		14,834			32,000		(2)	—

	Aviation Business Park	Maryland		50	%		5,748			—			—

	Rivers Park I and II(3)	Maryland		25	%		2,249			28,000		(2)	2,800

							$	47,482		$	110,000		$	2,800


				2013
		Reporting Segment		Ownership			Company			Debt			Recourse
				Interest			Investment						Debt(1)
	Prosperity Metro Plaza	Northern Virginia		51	%		$	24,735		$	48,991	(4)	$	—

	1750 H Street, NW	Washington, D.C.		50	%		16,780			28,413		(4)	—

	Aviation Business Park	Maryland		50	%		5,008			—			—

	Rivers Park I and II(3)	Maryland		25	%		2,627			28,000			7,000

							$	49,150		$	105,404		$	7,000



	(1)	We believe the fair value of the potential liability to us related to the recourse debt is inconsequential as the likelihood of our need to perform under the debt agreement is remote.

	(2)	During 2014, the mortgage loans that encumbered Prosperity Metro Plaza and 1750 H Street, NW matured and were replaced with new mortgage loans and the mortgage loan that encumbered Rivers Park I and II was refinanced. See below for details.

	(3)	Rivers Park I and Rivers Park II are owned through two separate joint ventures.

	(4)	Excludes the unamortized fair value adjustments recorded at acquisition upon the assumption of the mortgage loans.
Net Assets of Company's Unconsolidated Joint Ventures	The net assets of our unconsolidated joint ventures consisted of the following at December 31 (dollars in thousands):


		2014				2013
	Assets:
	Rental property, net	$	193,533			$	194,240

	Cash and cash equivalents	4,567				3,680

	Other assets	16,748				15,585

	Total assets	214,848				213,505

	Liabilities:
	Mortgage loans(1)	110,000				106,384

	Other liabilities	7,256				5,046

	Total liabilities	117,256				111,430

	Net assets	$	97,592			$	102,075



	(1)	The 2013 figures include the unamortized fair value adjustments recorded at acquisition upon the assumption of mortgage loans. During 2014, the mortgage loans that encumbered Prosperity Metro Plaza and 1750 H Street, NW matured and were replaced with new mortgage loans and the mortgage loan that encumbered Rivers Park I and II was refinanced. See above for details.
Results of Operations of Company's Unconsolidated Joint Ventures	The following table summarizes the results of operations of our unconsolidated joint ventures at December 31, 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 (amounts in thousands):



		2014				2013			2012
	Total revenues	$	23,285			$	24,017		$	24,945

	Total operating expenses	(7,408		)		(7,753		)	(7,377		)
	Net operating income	15,877				16,264			17,568

	Depreciation and amortization	(9,893		)		(11,551		)	(12,564		)
	Interest expense, net	(3,890		)		(4,222		)	(4,326		)
	Provision for income taxes	(63		)		(83		)	(21		)
	Contingent consideration charge	126				—			—

	Net income	$	2,157			$	408		$	657

Notes_Receivable_Tables

Notes Receivable (Tables)	12 Months Ended
	Dec. 31, 2014
Receivables [Abstract]
Summary of Notes Receivable	Below is a summary of our notes receivable for our outstanding mezzanine loans at December 31, 2014 and 2013 (dollars in thousands):



		Balance at December 31, 2014
	Property	Face Amount		Unamortized			Balance		Interest Rate
				Origination Fees
	950 F Street, NW	$	34,000	$	—		$	34,000	9.75	%

	America's Square	29,720		(41		)	29,679		9	%

		$	63,720	$	(41	)	$	63,679




		Balance at December 31, 2013
	Property	Face Amount		Unamortized			Balance		Interest Rate
				Origination Fees
	950 F Street, NW	$	25,000	$	(130	)	$	24,870	12.5	%

	America's Square	29,896		(70		)	29,826		9	%

		$	54,896	$	(200	)	$	54,696

Intangible_Assets_and_Deferred1

Intangible Assets and Deferred Market Rent Liabilities (Tables)	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets and Deferred Market Rent Liabilities	Intangible assets and deferred market rent liabilities consisted of the following at December 31 (amounts in thousands):



		2014(1)							2013(1)
		Gross		Accumulated			Net		Gross		Accumulated			Net
		Intangibles		Amortization			Intangibles		Intangibles		Amortization			Intangibles
	In-place leases	$	51,258	$	(22,443	)	$	28,815	$	44,772	$	(18,843	)	$	25,929

	Customer relationships	906		(654		)	252		1,002		(591		)	411

	Leasing commissions	11,335		(4,272		)	7,063		7,796		(3,361		)	4,435

	Legal leasing fees	377		(118		)	259		137		(83		)	54

	Deferred market rent assets	3,906		(1,309		)	2,597		2,485		(1,348		)	1,137

	Goodwill	6,930		—			6,930		6,930		—			6,930

		$	74,712	$	(28,796	)	$	45,916	$	63,122	$	(24,226	)	$	38,896

	Deferred market rent liability	$	5,193	$	(2,348	)	$	2,845	$	4,381	$	(2,767	)	$	1,614



	(1)	Includes amounts from properties that were classified as held-for-sale at December 31, 2014 and 2013.
Projected Net Amortization of Intangible Assets and Deferred Market Liabilities Including Amounts from Properties Classified as Held-For-Sale	The projected net amortization of intangible assets and deferred market liabilities as of December 31, 2014, including amounts from properties that were classified as held-for-sale at December 31, 2014, are as follows (amounts in thousands):



	2015	$	10,747

	2016	8,745

	2017	4,275

	2018	2,707

	2019	2,393

	Thereafter	7,274

		$	36,141

Dispositions_Tables

Dispositions (Tables)	12 Months Ended
	Dec. 31, 2014
Discontinued Operations and Disposal Groups [Abstract]
Discontinued Operations Square Feet Area	The following table is a summary of completed property dispositions whose operating results are included in continuing operations in our consolidated statements of operations for the periods presented (dollars in thousands):



		Reporting	Disposition Date	Property Type	Square Feet		Net Sale Proceeds
		Segment
	Owings Mills Business Park	Maryland	10/16/14	Business Park	180,475		$	12,417

	Corporate Campus at Ashburn Center	Northern Virginia	6/26/14	Business Park	194,184		39,910

Summary of Completed and Anticipated Property Dispositions	The following table is a summary of completed and anticipated property dispositions whose operating results are reflected as discontinued operations in our consolidated statements of operations for the periods presented (dollars in thousands):



		Reporting Segment		Disposition		Property Type		Square		Net Sale
				Date				Feet		Proceeds
	Richmond Portfolio(1)	Southern Virginia		TBD		Business Park		827,900		$ N/A

	Patrick Center	Maryland		4/16/14		Office		66,269		10,888

	West Park	Maryland		4/2/14		Office		28,333		2,871

	Girard Business Center and Gateway Center	Maryland		1/29/14		Business Park and Office		341,973		31,616

	Worman’s Mill Court	Maryland		11/19/13		Office		40,099		3,362

	Triangle Business Center	Maryland		9/27/13		Business Park		74,429		2,732

	4200 Tech Court	Northern Virginia		8/15/13		Office		33,875		3,210

	Industrial Portfolio(2)	Various		May/June 2013		Industrial		4,280,985		176,569

	4212 Tech Court	Northern Virginia		6/5/13		Office		32,055		2,469

	Owings Mills Business Park(3)	Maryland		11/7/12		Business Park		38,779		3,472

	Goldenrod Lane	Maryland		5/31/12		Office		23,518		2,663

	Woodlands Business Center	Maryland		5/8/12		Office		37,887		2,885

	Airpark Place Business Center	Maryland		3/22/12		Business Park		82,429		5,153



	(1)	Effective as of February 9, 2015, we entered a binding contract to sell the Richmond Portfolio, which we anticipate closing in the first half of 2015. However, we can provide no assurances regarding the timing or pricing of the sale of the Richmond Portfolio, or that the sale will occur at all. We classified the Richmond Portfolio as held-for-sale at December 31, 2014.

	(2)	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.

	(3)	In November 2012, we sold two of the six buildings at Owings Mills Business Park. The remaining four buildings at Owings Mills Business Park were sold in October 2014 and their results of operations are included in continuing operations in our consolidated statements of operations. See note 10(a) Dispositions - Disposed or Held-for-Sale Properties within Continuing Operations.
Net Income from Discontinued Operations	The following table summarizes the results of operations of properties included in discontinued operations for the years ended December 31 (dollars in thousands):



		2014				2013			2012

	Revenues	$	7,688			$	31,654		$	50,985

	Property operating expenses	(3,612		)		(10,564		)	(16,226		)

	Depreciation and amortization	(3,662		)		(8,937		)	(14,958		)

	Interest expense, net of interest income	(268		)		(1,268		)	(2,947		)

	Impairment of rental property	—				(4,092		)	(1,072		)

	Income from operations of disposed property	146				6,793			15,782

	Loss on debt extinguishment	—				(4,414		)	—

	Gain on sale of rental property	1,338				19,363			161

	Net income from discontinued operations	$	1,484			$	21,742		$	15,943

	The following table summarizes the aggregate results of operations for the two properties that are included in continuing operations for the periods presented (dollars in thousands):



		2014				2013			2012
	Revenues	$	2,920			$	5,223		$	5,363

	Property operating expenses	(1,172		)		(1,521		)	(1,375		)
	Depreciation and amortization	(1,047		)		(1,424		)	(1,517		)
	Interest expense, net of interest income	—				—			(230		)

	Impairment of rental property	(3,956		)		—			(3,246		)

	(Loss) income from operations of disposed property	(3,255		)		2,278			(1,005		)

	Loss on debt extinguishment	—				—			(466		)

	Gain on sale of rental property	21,230				—			—

	Net income (loss) from continuing operations	$	17,975			$	2,278		$	(1,471	)

Debt_Tables

Debt (Tables)	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Schedule of Borrowings	Our borrowings consisted of the following at December 31 (dollars in thousands):



		2014				2013
	Mortgage loans, effective interest rates ranging from 4.40% to 6.63%, maturing at various dates through June 2023(1)(2)	$	308,637			$	274,648

	Unsecured term loan, effective interest rates ranging from LIBOR plus 1.65% to LIBOR plus 2.05%, with staggered maturity dates ranging from October 2018 to October 2020(1)	300,000				300,000

	Unsecured revolving credit facility, effective interest rate of LIBOR plus 1.70%, maturing October 2017(1)	205,000				99,000

		$	813,637			$	673,648



	(1)	At December 31, 2014, LIBOR was 0.17%. All references to LIBOR in the consolidated financial statements refer to one-month LIBOR.

	(2)	Includes five mortgage loans that will be repaid upon the sale of the Richmond Portfolio, which is expected to be sold in the first half of 2015. At December 31, 2014 and 2013, the mortgage loans had an aggregate principal balance of $3.5 million and $4.5 million, respectively, and were classified within “Liabilities held-for-sale” on our consolidated balance sheets for the periods presented.
Summary of Company's Mortgage Debt	The following table provides a summary of our mortgage debt at December 31, 2014 and 2013 (dollars in thousands):



	Encumbered Property	Contractual			Effective			Maturity	31-Dec-14				31-Dec-13
		Interest Rate			Interest			Date
					Rate
	Annapolis Business Center(1)	5.74	%		6.25	%		Jun-14	$	—			$	8,076

	Jackson National Life Loan(2)	5.19	%		5.19	%		Aug-15	64,943				66,116

	440 First Street, NW Construction Loan(3)(4)	LIBOR + 2.50%			LIBOR + 2.50%			May-16	32,216				21,699

	Storey Park Land Loan(3)(5)	LIBOR + 2.50%			LIBOR + 2.50%			Oct-16	22,000				22,000

	Gateway Centre Manassas Building I	7.35	%		5.88	%		November 2016	432				638

	Hillside I and II	5.75	%		4.62	%		December 2016	12,949				13,349

	Redland Corporate Center Buildings II & III	4.2	%		4.64	%		Nov-17	65,816				67,038

	840 First Street, NE	5.72	%		6.01	%		Jul-20	36,539				37,151

	Battlefield Corporate Center	4.26	%		4.4	%		Nov-20	3,692				3,851

	1211 Connecticut Avenue, NW	4.22	%		4.47	%		Jul-22	29,691				30,249

	1401 K Street, NW	4.8	%		4.93	%		Jun-23	36,861				—

					4.75	%	(6)		305,139				270,167

	Unamortized fair value adjustments								(370		)		(554		)
	Principal balance								304,769				269,613


	Richmond Portfolio(7)
	Hanover Business Center Building D	8.88	%		6.63	%		Aug-15	104				252

	Chesterfield Business Center Buildings C,D,G and H	8.5	%		6.63	%		Sep-15	302				681

	Hanover Business Center Building C	7.88	%		6.63	%		Dec-17	505				653

	Chesterfield Business Center Buildings A,B,E and F	7.45	%		6.63	%		Jun-21	1,674				1,873

	Airpark Business Center	7.45	%		6.63	%		Jun-21	913				1,022

									3,498				4,481

	Total unamortized fair value adjustments - Richmond(3)								(73		)		(109		)
	Total principal balance - Richmond(3)								$	3,425			$	4,372


	Total principal balance				4.75	%	(6)		$	308,194			$	273,985



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

	(2)	At December 31, 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 December 31, 2014, LIBOR was 0.17%.

	(4)	At December 31, 2014, 50% of the principal balance and any unpaid accrued interest on the 440 First Street, NW construction loan were recourse to us. In 2014, we borrowed an additional $10.5 million under the construction loan.

(5)	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.

(6)	Weighted average interest rate on total mortgage debt.

(7)	The mortgage loans that encumber properties within the Richmond Portfolio were classified within “Liabilities held-for-sale” on our consolidated balance sheets for the periods presented and will be repaid upon the sale of the Richmond Portfolio, which is expected to be sold in the first half of 2015.
Originated or Assumed Mortgages	We have originated or assumed the following mortgage loans since January 1, 2013 (dollars in thousands):



	Month		Year		Property		Effective		Principal
							Interest		Amount
							Rate
	October		2014		Storey Park Land Loan(1)		LIBOR + 2.50%		$	22,000		(1)

	April		2014		1401 K Street, NW		4.93	%	37,269

	June		2013		440 First Street, NW Construction Loan(2)		5	%	21,699			(2)



	(1)	We have a 97% ownership interest in the property through a consolidated joint venture. The loan balance in the chart above reflects the entire loan balance, which is reflected in our consolidated balance sheets.

	(2)	At December 31, 2014, 50% of the principal balance and any unpaid accrued interest on the 440 First Street, NW construction loan were recourse to us. In 2014, we borrowed an additional $10.5 million under the construction loan.
Repayment of Mortgages	We have repaid the following mortgage loans since January 1, 2013 (dollars in thousands):



	Month		Year		Property		Effective		Principal
							Interest		Balance
							Rate		Repaid
	October		2014		Storey Park Land Loan		5.8	%	$	22,000

	May		2014		Annapolis Business Center		6.25	%	8,027

	September		2013		840 First Street, NE(1)		6.05	%	53,877

	September		2013		Linden Business Center		5.58	%	6,622

	June		2013		Cloverleaf Center		6.75	%	16,427

	June		2013		Mercedes Center – Note 1		6.04	%	4,799

	June		2013		Mercedes Center – Note 2		6.3	%	9,260

	June		2013		Jackson National Life Loan -Northridge		5.19	%	6,985

	May		2013		Jackson National Life Loan - I-66 Commerce Center		5.19	%	21,695

	February		2013		1434 Crossways Boulevard, Building I		5.38	%	7,597

	February		2013		TenThreeTwenty		7.29	%	13,273

	February		2013		Cedar Hill		6.58	%	15,364

	January		2013		Prosperity Business Center		5.75	%	3,242



	(1)	On September 30, 2013, we repaid a $53.9 million mortgage loan that encumbered 840 First Street, NE, which was scheduled to mature on October 1, 2013. Simultaneously with the repayment of the mortgage debt, we encumbered 840 First Street, NE with a $37.3 million mortgage loan that had previously encumbered 500 First Street, NW.
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 December 31, 2014 (dollars in thousands):


		Maturity Date		Amount				Interest Rate(1)
	Tranche A	Oct-18		$	100,000			LIBOR, plus 165 basis points

	Tranche B	Oct-19		100,000				LIBOR, plus 180 basis points

	Tranche C	October 2020		100,000				LIBOR, plus 205 basis points

				$	300,000


	(1)	At December 31, 2014, LIBOR was 0.17%. The interest rate spread is subject to change based on our maximum total indebtedness ratio. For more information, see note 11(e) Debt – Financial Covenants.
Aggregate Debt Maturities	Our aggregate debt maturities as of December 31, 2014, including amounts from properties that were classified as held-for-sale at December 31, 2014, are as follows (dollars in thousands):



	2015		$	69,553

	2016		70,763

	2017		270,999

	2018		102,746

	2019		102,894

	Thereafter		196,239

			813,194

	Unamortized fair value adjustments		443

	Total contractual principal balance		$	813,637

Derivative_Instruments_Tables

Derivative Instruments (Tables)	12 Months Ended
	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Summary of Interest Rate Swap Agreements	At December 31, 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):



	Maturity Date	Notional		Interest Rate	Fixed LIBOR
		Amount		Contractual	Interest Rate
				Component
	Jul-16	$	35,000	LIBOR	1.754	%

	Jul-16	25,000		LIBOR	1.763	%

	Jul-17	30,000		LIBOR	2.093	%

	Jul-17	30,000		LIBOR	2.093	%

	Jul-18	30,000		LIBOR	1.66	%

	Jul-18	25,000		LIBOR	1.394	%

	Jul-17	25,000		LIBOR	1.129	%

	Jul-17	12,500		LIBOR	1.129	%

	Jul-18	12,500		LIBOR	1.383	%

	Jul-17	50,000		LIBOR	0.955	%

	Jul-18	25,000		LIBOR	1.135	%

	Total/Weighted Average	$	300,000		1.505	%

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 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 December 31, 2014 and 2013 (amounts in thousands):



		Balance at December 31, 2014		Level 1		Level 2		Level 3
	Recurring Measurements:
	Derivative instrument-swap assets	$	133	$	—	$	133	$	—

	Derivative instrument-swap liabilities	3,569		—		3,569		—




		Balance at December 31, 2013		Level 1		Level 2		Level 3
	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 amount and estimated fair value of our notes receivable and debt instruments at December 31 are as follows (amounts in thousands):



		2014				2013
		Carrying		Fair		Carrying		Fair
		Value		Value		Value		Value
	Financial Assets:
	Notes receivable(1)	$	63,679	$	63,720	$	54,696	$	56,812

	Financial Liabilities:
	Mortgage debt(2)	$	308,637	$	292,882	$	274,648	$	262,873

	Unsecured term loan	300,000		300,000		300,000		300,000

	Unsecured revolving credit facility	205,000		205,000		99,000		99,000

	Total	$	813,637	$	797,882	$	673,648	$	661,873



	(1)	The principal amount of our notes receivable was $63.7 million and $54.9 million at December 31, 2014 and 2013, respectively. On January 27, 2015, the owners of America’s Square, a 461,000 square foot office complex located in Washington, D.C., gave notice of their intent to prepay, on or about February 24, 2015, a mezzanine loan, which has an outstanding $29.7 million balance of the $30.0 million mezzanine loan that we provided them in April 2011.

	(2)	Includes the mortgage debt balance of our Richmond portfolio properties, which have been classified as held-for-sale and is reflected in "Liabilities held-for-sale" on our consolidated balance sheets.

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Summary of Operating Leases Generating Future Minimum Rental Payments	Our rental properties are subject to non-cancelable operating leases generating future minimum contractual rent payments due from tenants, which as of December 31, 2014 are as follows (dollars in thousands):



		Future minimum
		contractual
		rent payments
	2015	$	133,834

	2016	127,967

	2017	104,975

	2018	90,376

	2019	76,520

	Thereafter	214,378

		$	748,050

Schedule of Future Minimum Rental Payments	Future minimum rental payments under our corporate office leases as of December 31, 2014 are summarized as follows, net of sublease revenue (dollars in thousands):



		Future minimum
		rent payments
	2015	$	1,450

	2016	1,489

	2017	1,529

	2018	1,911

	2019	1,995

	Thereafter	2,224

		$	10,598

Equity_Tables

Equity (Tables)	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Characterization of Company's Dividends	The characterization of the dividends declared on our common and preferred shares for 2014, 2013 and 2012 are as follows:



		Common Shares						Preferred Shares
		2014		2013		2012		2014		2013		2012(2)
	Ordinary income(1)	72.42	%	13.53	%	—		100	%	100	%	19.83	%

	Return of capital	27.58	%	86.47	%	100	%	—		—		27.27	%

	Capital gains	—		—		—		—		—		52.9	%



	(1)	The dividends classified above as ordinary income do not represent “qualified dividend income” and, therefore, are not eligible for reduced rates.

	(2)	Figures are estimates.

Noncontrolling_Interests_Table

Noncontrolling Interests (Tables)	12 Months Ended
	Dec. 31, 2014
Noncontrolling Interest [Abstract]
Summary of Redeemable Noncontrolling Interests in Operating Partnership	The redeemable noncontrolling interests in the Operating Partnership for the three years ended December 31 are as follows (amounts in thousands):



		Redeemable
		noncontrolling
		interests
	Balance at December 31, 2012	$	34,367

	Net loss	(74		)
	Changes in ownership, net	143

	Distributions to owners	(1,557		)
	Other comprehensive income	342

	Balance at December 31, 2013	33,221

	Net income	199

	Changes in ownership, net	1,465

	Distributions to owners	(1,578		)
	Other comprehensive income	25

	Balance at December 31, 2014	$	33,332

Benefit_Plans_Tables

Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Compensation Plans Option Activity	A summary of our stock option activity for the three years ended December 31 is presented below:


		Options		Weighted			Weighted Average		Aggregate
				Average			Remaining		Intrinsic
				Exercise Price			Contractual Term		Value
	Outstanding at December 31, 2011	887,168		$	16.76		4.4 years		$	293,930

	Granted	627,500		14.7

	Exercised	(7,326	)	9.63

	Forfeited	(123,336	)	16.25

	Outstanding at December 31, 2012	1,384,006		15.91			5.9 years		$	174,763

	Granted	124,250		12.73

	Exercised	(14,733	)	11.05

	Expired	(298,469	)	15

	Forfeited	(105,762	)	16.17

	Outstanding at December 31, 2013	1,089,292		15.83			6.6 years		$	109,151

	Granted	135,250		11.61

	Exercised	(17,171	)	10.1

	Expired	(57,500	)	19.08

	Forfeited	(98,512	)	14.49

	Outstanding at December 31, 2014	1,051,359		$	15.33		6.3 years		$	181,352

	Exercisable at December 31:
	2014	552,620		$	16.49		5.1 years		$	102,039

	2013	521,723		17.25			4.9 years		109,151

	2012	693,854		17.01			2.9 years		162,593

	Options expected to vest, subsequent to December 31, 2014	485,733		$	14.11		7.5 years		$	71,358

Stock Options Information	The following table summarizes information about our stock options at December 31, 2014:


				Options Outstanding							Options Exercisable
	Year	Range of		Options		Weighted Average		Weighted			Options	Weighted
	Issued	Exercise Prices				Remaining		Average				Average
						Contractual Life		Exercise Price				Exercise Price
	2005	$22.42 - 22.54		59,000		0.0 years		$	22.44		59,000	$	22.44

	2006	26.6		17,350		1.0 year		26.6			17,350	26.6

	2007	29.11 - 29.24		31,500		2.0 years		29.13			31,500	29.13

	2008	17.29		39,000		3.0 years		17.29			39,000	17.29

	2009	9.3		33,346		4.0 years		9.3			33,346	9.3

	2010	12.57		42,705		5.0 years		12.57			42,705	12.57

	2011	15.17 - 17.12		77,188		6.1 years		16.36			72,664	16.37

	2012	13.54 - 15.00		566,533		7.0 years		14.83			219,678	14.68

	2013	12.73		78,987		8.0 years		12.73			37,377	12.73

	2014	11.61		105,750		9.0 years		11.61			—	—

				1,051,359		6.3 years		15.33			552,620	16.49

Assumptions Used in Fair Value Determination of Stock Options Granted	The weighted average assumptions used in the fair value determination of stock options granted to employees for the years ended December 31 are summarized as follows:



		2014		2013		2012
	Risk-free interest rate	1.72	%	0.76	%	1.28	%
	Expected volatility	39	%	49.7	%	45.6	%
	Expected dividend yield	4.66	%	4.92	%	5.71	%
	Weighted average expected life of options	5.0 years		5.0 years		6.6 years

Summary of Company's Non-Vested Share Awards	A summary of our non-vested common share awards at December 31, 2014 is as follows:



		Non-vested		Weighted Average
		Shares		Grant Date
				Fair Value
	Non-vested at December 31, 2011	748,968		$	12.67

	Granted	355,612		13.87

	Vested	(309,605	)	13.52

	Expired	(61,944	)	11.36

	Forfeited	(59,203	)	15.03

	Non-vested at December 31, 2012	673,828		12.83

	Granted	313,086		12.14

	Vested	(297,778	)	12.89

	Expired	(45,049	)	11.42

	Forfeited	(6,425	)	14.01

	Non-vested at December 31, 2013	637,662		13.33

	Granted	164,675		12.84

	Vested	(137,924	)	14.21

	Expired	(29,514	)	10.21

	Forfeited	(11,478	)	13.04

	Non-vested at December 31, 2014	623,421		$	13.16

Segment_Information_Tables

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Summary of Segment Information	The results of operations for our four reporting segments for the three years ended December 31 are as follows (dollars in thousands):



		2014
		Washington, D.C.				Maryland				Northern Virginia				Southern Virginia				Consolidated
	Number of buildings(1)	6				38				49				38				131

	Square feet(1)	917,008				1,999,332				3,021,509				2,852,298				8,790,147

	Total revenues	$	33,959			$	45,767			$	53,645			$	28,281			$	161,652

	Property operating expense	(9,683		)		(11,482		)		(13,352		)		(8,735		)		(43,252		)
	Real estate taxes and insurance	(5,583		)		(3,907		)		(5,592		)		(2,278		)		(17,360		)
	Total property operating income	$	18,693			$	30,378			$	34,701			$	17,268			101,040

	Depreciation and amortization expense																	(61,796		)

	General and administrative																	(21,156		)

	Acquisition costs																	(2,681		)

	Impairment of rental property																	(3,956		)

	Other income																	4,108

	Income from discontinued operations																	1,484

	Net income																	$	17,043

	Total assets(2)(3)	$	505,842			$	360,470			$	439,833			$	228,306			$	1,618,460

	Capital expenditures(4)	$	23,422			$	10,185			$	7,816			$	8,436			$	50,789




		2013
		Washington, D.C.				Maryland				Northern Virginia				Southern Virginia				Consolidated
	Number of buildings(1)(5)	4				53				51				38				146

	Square feet(1)(5)	522,605				2,638,988				3,086,057				2,852,471				9,100,121

	Total revenues	$	28,208			$	41,735			$	51,787			$	27,085			$	148,815

	Property operating expense	(6,693		)		(10,579		)		(12,601		)		(8,407		)		(38,280		)
	Real estate taxes and insurance	(4,792		)		(3,436		)		(5,679		)		(2,167		)		(16,074		)
	Total property operating income	$	16,723			$	27,720			$	33,507			$	16,511			94,461

	Depreciation and amortization expense																	(54,567		)

	General and administrative																	(21,979		)

	Acquisition costs																	(602		)

	Contingent consideration related to acquisition of property																	213

	Other expenses																	(28,287		)

	Income from discontinued operations																	21,742

	Net income																	10,981

	Total assets(2)(3)	$	344,739			$	430,498			$	423,839			$	230,175			$	1,502,460

Capital expenditures(4)	$	26,910			$	16,216			$	13,685			$	10,106			$	68,002




	2012
	Washington, D.C.				Maryland				Northern Virginia				Southern Virginia				Consolidated
Number of buildings(6)	3				62				56				57				178

Square feet(6)	531,714				3,781,379				3,654,527				5,483,781				13,451,401

Total revenues	$	27,718			$	41,726			$	47,207			$	26,311			$	142,962

Property operating expense	(5,298		)		(9,862		)		(11,519		)		(7,643		)		(34,322		)
Real estate taxes and insurance	(3,876		)		(3,170		)		(5,020		)		(2,119		)		(14,185		)
Total property operating income	$	18,544			$	28,694			$	30,668			$	16,549			94,455

Depreciation and amortization expense																	(51,457		)

General and administrative																	(23,568		)

Acquisition costs																	(49		)

Contingent consideration related to acquisition of property																	(152		)

Impairment of rental property																	(2,444		)
Other expenses																	(45,251		)

Benefit from income taxes																	4,142

Income from discontinued operations																	15,943

Net loss																	$	(8,381	)

Total assets(2)(3)	$	321,875			$	493,267			$	462,667			$	364,514			$	1,717,748

Capital expenditures(4)	$	12,023			$	23,163			$	20,959			$	12,897			$	70,486



(1)	Excludes Storey Park from our Washington, D.C. reporting segment, which was placed in development in the third quarter of 2013.

(2)	Total assets include our investment in properties that are owned through joint ventures that are not consolidated within our consolidated financial statements. For more information on our unconsolidated investments, including location within our reportable segments, see note 6, Investment in Affiliates.

(3)	Corporate assets not allocated to any of our reportable segments totaled $84,009, $73,209 and $75,425 at December 31, 2014, 2013 and 2012, respectively.

(4)	Capital expenditures for corporate assets not allocated to any of our reportable segments totaled $930, $1,085 and $1,444 at December 31, 2014, 2013 and 2012, respectively.

(5)	Includes occupied space at 440 First Street, NW in our Washington, D.C. reporting segment, which was substantially completed in the third quarter of 2013. In 2014, the property was placed in service.

(6)	Our Washington, D.C. reporting segment excludes 440 First Street, NW, which was in redevelopment during 2012.

Quarterly_Financial_Informatio1

Quarterly Financial Information (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Summary of Quarterly Financial Information

		2014(1)
		First			Second			Third			Fourth
	(amounts in thousands, except per share amounts)	Quarter			Quarter			Quarter			Quarter
	Revenues	$	39,363		$	39,307		$	40,055		$	42,928

	Operating expenses	35,744			39,579			36,283			38,595

	Operating income (loss)	3,619			(272		)	3,772			4,333

	(Loss) income from continuing operations	(586		)	16,796			(248		)	(402		)

	(Loss) income from discontinued operations	(857		)	1,538			297			505

	Less: Net loss (income) attributable to noncontrolling interests	195			(652		)	131			128

	Net (loss) income attributable to First Potomac Realty Trust	(1,248		)	17,682			180			231

	Less: Dividends on preferred shares	(3,100		)	(3,100		)	(3,100		)	(3,100		)
	Net (loss) income attributable to common shareholders	$	(4,348	)	$	14,582		$	(2,920	)	$	(2,869	)

	Basic and diluted earnings per common share:
	(Loss) income from continuing operations	$	(0.07	)	$	0.22		$	(0.05	)	$	(0.06	)

	(Loss) income from discontinued operations	(0.01		)	0.03			—			0.01

	Net (loss) income	$	(0.08	)	$	0.25		$	(0.05	)	$	(0.05	)




		2013(1)
		First			Second			Third			Fourth
	(amounts in thousands, except per share amounts)	Quarter			Quarter			Quarter			Quarter
	Revenues	$	37,179		$	36,915		$	37,206		$	37,517

	Operating expenses	32,508			31,221			33,663			33,899

	Operating income	4,671			5,694			3,543			3,618

	Loss from continuing operations	(3,638		)	(2,192		)	(2,509		)	(2,421		)
	Income (loss) from discontinued operations	5,601			16,668			792			(1,320		)

	Less: Net loss (income) attributable to noncontrolling interests	59			(466		)	211			288

	Net income (loss) attributable to First Potomac Realty Trust	2,022			14,010			(1,506		)	(3,453		)

	Less: Dividends on preferred shares	(3,100		)	(3,100		)	(3,100		)	(3,100		)
	Net (loss) income attributable to common shareholders	$	(1,078	)	$	10,910		$	(4,606	)	$	(6,553	)

	Basic and diluted earnings per common share:
	Loss from continuing operations	$	(0.13	)	$	(0.10	)	$	(0.09	)	$	(0.09	)
	Income (loss) from discontinued operations	0.11			0.3			0.01			(0.02		)

	Net (loss) income	$	(0.02	)	$	0.2		$	(0.08	)	$	(0.11	)



	(1)	These figures are rounded to the nearest thousand, which may impact cross-footing in reconciling to full year totals.

Description_of_Business_Additi

Description of Business - Additional Information (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	sqft				sqft				Property	sqft	sqft
	Person								JointVenture
	Rate								sqft
									Person
									Rate
Real Estate Properties [Line Items]
Operating Partnership in preferred	100.00%								100.00%
Interest in Operating Partnership	95.70%								95.70%
Square Feet	8,790,147				9,100,121				8,790,147	9,100,121	13,451,401
Unconsolidated joint ventures									5
Square footage of land for additional development	1,400,000								1,400,000
Occupancy rate in the Company's consolidated properties	87.90%								87.90%
Number Of Tenants In Companys Consolidated Rental Properties	582								582
Square footage in development or redevelopment not included on occupancy calculation	200,000								200,000
Annualized Cash Basis Rent Percent for Government Tenant	14.00%								14.00%
Percentage of outstanding account receivables accounted by government	26.00%								26.00%
Revenues	$42,928	$40,055	$39,307	$39,363	$37,517	$37,206	$36,915	$37,179	$161,652	$148,815	$142,962
Consolidated Total assets	$1,618,460				$1,502,460				$1,618,460	$1,502,460	$1,717,748
Number of separate reporting segments of properties									4
Wholly-owned Properties [Member]
Real Estate Properties [Line Items]
Square Feet	8,800,000								8,800,000
Unconsolidated Properties [Member]
Real Estate Properties [Line Items]
Square Feet	900,000								900,000

Summary_of_Significant_Account3

Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounting Policies [Abstract]
Charges of Uncollectible		$1,100,000	$800,000	$700,000
Lease termination fees included in "Tenant reimbursements and other revenues"		1,100,000	1,000,000	2,000,000
Age of highly liquid investments considered as cash equivalents	90 days or less	90 days or less
Accumulated amortization of financing costs related to long-term debt	24,800,000	24,800,000	20,700,000
Required distribution percentage of ordinary annual taxable income to shareholders to maintain Company status as a REIT	90.00%	90.00%
Required distribution percentage of REIT taxable income of the Company to shareholders to avoid federal income tax and non-deductible exercise tax	100.00%	100.00%
Percentage of likelihood that the Company may recognize tax benefit from uncertain tax position when it is more-likely-than-not that the position will be sustained, based on technical merits	50.00%	50.00%
Uncertain tax positions		0	0	0
Allowance for credit losses for its notes receivable		$0	$0	$0

Summary_of_Significant_Account4

Summary of Significant Accounting Policies - Scheduled Future Amortization for Deferred Financing and Leasing Costs (Detail) (USD $)	Dec. 31, 2014
Amortization Expense [Line Items]
Future Amortization Expense for Deferred Financing Cost	$6,160,000
Future Amortization Expense for Deferred Leasing Cost	28,874,000
Lease Incentive	4,414,000
Excluded leasing costs amortization for tenants not yet placed in-service	5,600,000
2015 [Member]
Amortization Expense [Line Items]
Future Amortization Expense for Deferred Financing Cost	1,905,000
Future Amortization Expense for Deferred Leasing Cost	5,446,000
Lease Incentive	637,000
2016 [Member]
Amortization Expense [Line Items]
Future Amortization Expense for Deferred Financing Cost	1,533,000
Future Amortization Expense for Deferred Leasing Cost	4,977,000
Lease Incentive	637,000
2017 [Member]
Amortization Expense [Line Items]
Future Amortization Expense for Deferred Financing Cost	1,153,000
Future Amortization Expense for Deferred Leasing Cost	4,181,000
Lease Incentive	552,000
2018 [Member]
Amortization Expense [Line Items]
Future Amortization Expense for Deferred Financing Cost	836,000
Future Amortization Expense for Deferred Leasing Cost	3,593,000
Lease Incentive	518,000
2019 [Member]
Amortization Expense [Line Items]
Future Amortization Expense for Deferred Financing Cost	308,000
Future Amortization Expense for Deferred Leasing Cost	2,828,000
Lease Incentive	443,000
Thereafter [Member]
Amortization Expense [Line Items]
Future Amortization Expense for Deferred Financing Cost	425,000
Future Amortization Expense for Deferred Leasing Cost	7,849,000
Lease Incentive	$1,627,000

Summary_of_Significant_Account5

Summary of Significant Accounting Policies - Estimated Useful Lives of Company's Assets, by Class (Detail)	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Tenant improvements, Useful life	useful life of the asset or the term of the related lease
Buildings [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	39 years
Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	5 years
Minimum [Member] \| Building and Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	5 years
Minimum [Member] \| Furniture, Fixtures and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	5 years
Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	39 years
Maximum [Member] \| Building and Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	20 years
Maximum [Member] \| Furniture, Fixtures and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	15 years

Summary_of_Significant_Account6

Summary of Significant Accounting Policies - Intangible Assets (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Acquired Indefinite-lived Intangible Assets [Line Items]
Goodwill, Fair Value Disclosure	$2,100,000
Goodwill, Impairment Loss	0	0	0
Uncertain tax positions	0	0	0
Allowance for credit losses for its notes receivable	0	0	0
Eight Four Zero First Street [Member]
Acquired Indefinite-lived Intangible Assets [Line Items]
Goodwill			$4,800,000

Earnings_Per_Common_Share_Comp

Earnings Per Common Share - Computation of Company's Basic and Diluted Earnings Per Share (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Numerator for basic and diluted earnings per common share:
Income (loss) from continuing operations	($402)	($248)	$16,796	($586)	($2,421)	($2,509)	($2,192)	($3,638)	$15,559	($10,761)	($24,324)
Income from discontinued operations	505	297	1,538	-857	-1,320	792	16,668	5,601	1,484	21,742	15,943
Net income (loss)									17,043	10,981	-8,381
Less: Net (income) loss from continuing operations attributable to noncontrolling interests									-135	1,047	1,780
Less: Net income from discontinued operations attributable to noncontrolling interests									-64	-954	-794
Net income (loss) attributable to First Potomac Realty Trust	231	180	17,682	-1,248	-3,453	-1,506	14,010	2,022	16,844	11,074	-7,395
Less: Dividends on preferred shares	-3,100	-3,100	-3,100	-3,100	-3,100	-3,100	-3,100	-3,100	-12,400	-12,400	-11,964
Net income (loss) attributable to common shareholders									4,444	-1,326	-19,359
Less: Allocation to participating securities									-314	-388	-620
Net income (loss) attributable to common shareholders	($2,869)	($2,920)	$14,582	($4,348)	($6,553)	($4,606)	$10,910	($1,078)	$4,130	($1,714)	($19,979)
Denominator for basic and diluted earnings per common share:
Weighted average common shares outstanding b basic									58,150	55,034	50,120
Weighted average common shares outstanding b diluted									58,220	55,034	50,120
Basic and diluted earnings per common share:
Income (loss) from continuing operations	($0.06)	($0.05)	$0.22	($0.07)	($0.09)	($0.09)	($0.10)	($0.13)	$0.05	($0.41)	($0.70)
Income from discontinued operations	$0.01	$0	$0.03	($0.01)	($0.02)	$0.01	$0.30	$0.11	$0.02	$0.38	$0.30
Net income (loss)	($0.05)	($0.05)	$0.25	($0.08)	($0.11)	($0.08)	$0.20	($0.02)	$0.07	($0.03)	($0.40)

Earnings_Per_Common_Share_Anti

Earnings Per Common Share - Anti-Dilutive Shares Not Included in Calculation of Diluted Earnings Per Share (Detail)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, Amount	14,136	13,916	14,177
Series A Preferred Shares, shares issued	6,400	6,400
Stock option awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, Amount	1,122	1,369	1,462
Non-vested share awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, Amount	398	471	553
Series A Preferred Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, Amount	12,616	12,076	12,162
Series A Preferred Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Series A Preferred Shares, shares issued				1,800

Rental_Property_Summary_of_Ren

Rental Property - Summary of Rental Property (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Land and land improvements	$325,214	$287,015
Buildings and improvements	949,683	807,198
Construction in process	69,181	93,174
Tenant improvements	159,867	138,543
Furniture, fixtures and equipment	427	4,250
Rental property, gross	1,504,372	1,330,180
Less: accumulated depreciation	-215,499	-185,725
Rental property, net	1,288,873	1,144,455
Richmond [Member] \| Southern Virginia [Member]
Property, Plant and Equipment [Line Items]
Rental property, net	$57,700	$102,400

Rental_Property_Additional_Inf

Rental Property - Additional Information (Detail) (USD $)	12 Months Ended	0 Months Ended
	Dec. 31, 2014	Aug. 04, 2013	Dec. 31, 2013	Oct. 15, 2013	Dec. 31, 2012
	sqft	acre	sqft	sqft	sqft
	Rate
Segment Reporting Information [Line Items]
Area of land available for development in additional building space	1,400,000
Square Feet	8,790,147		9,100,121		13,451,401
Original cost basis of the property	$949,683,000		$807,198,000
Lease expiration date	31-Jan-21
Anticipated completion of redevelopment				139,000
Leased Percentage	56.80%
Occupancy Percentage	36.30%
Projected incremental investment in redevelopment project	55,500,000
Completed and placed in-service redevelopment efforts	0
Development Efforts Yet To Be Placed In Service	0
440 First Street, NW [Member]
Segment Reporting Information [Line Items]
Original cost basis of the property	23,600,000
Washington, D.C Reporting Segment [Member]
Segment Reporting Information [Line Items]
Area of land available for development in additional building space	700,000
Projected incremental investment in development project	55,400,000
Original cost basis of the property	43,300,000
Lease expiration date		31-Aug-13
Development of area for operations by joint venture		1.6
Redevelopment efforts yet to be placed-in service	0
Maryland Reporting Segment [Member]
Segment Reporting Information [Line Items]
Area of land available for development in additional building space	100,000
Northern Virginia Reporting Segment [Member]
Segment Reporting Information [Line Items]
Area of land available for development in additional building space	500,000
Square Feet	167,000
Projected incremental investment in development project	6,900,000
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
Minimum [Member]
Segment Reporting Information [Line Items]
Estimated useful lives of the assets	5 years
Maximum [Member]
Segment Reporting Information [Line Items]
Estimated useful lives of the assets	39 years
Maximum [Member] \| Washington, D.C Reporting Segment [Member] \| Greyhound Property [Member]
Segment Reporting Information [Line Items]
Area of land available for development in additional building space		712,000

Acquisitions_Acquisitions_Deta

Acquisitions Acquisitions (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 24, 2014	Jun. 25, 2014	Apr. 08, 2014	Oct. 01, 2013
	sqft	sqft	sqft	Sep. 24, 2014	Jun. 25, 2014	Apr. 08, 2014	Oct. 01, 2013
Business Acquisition [Line Items]
Square Feet	8,790,147	9,100,121	13,451,401
Northern Virginia Reporting Segment [Member]
Business Acquisition [Line Items]
Square Feet	167,000
1401 K Street, NW [Member]
Business Acquisition [Line Items]
Business combination funding	37,300,000
Five Hundred Forty Gaither Road Redland First [Member]
Business Acquisition [Line Items]
Funding from sale of industrial portfolio		28,200,000
Office Building [Member] \| 11 DuPont Circle, NW [Domain] \| Washington, D.C. [Member]
Business Acquisition [Line Items]
Acquisition Date	24-Sep-14
Square Feet	153,018
Contractual Purchase Price				89,000,000
Office Building [Member] \| 1775 Wiehle Avenue [Domain] \| Northern Virginia Reporting Segment [Member]
Business Acquisition [Line Items]
Acquisition Date	25-Jun-14
Square Feet	130,048
Contractual Purchase Price					41,000,000
Office Building [Member] \| 1401 K Street, NW [Member] \| Washington, D.C. [Member]
Business Acquisition [Line Items]
Acquisition Date	8-Apr-14
Square Feet	118,292
Contractual Purchase Price						58,000,000
Office Building [Member] \| Five Hundred Forty Gaither Road Redland First [Member] \| Maryland Reporting Segment [Member]
Business Acquisition [Line Items]
Acquisition Date		1-Oct-13
Square Feet		133,895
Contractual Purchase Price							$30,000,000

Acquisitions_Additional_Inform

Acquisitions - Additional Information (Detail) (USD $)	12 Months Ended			3 Months Ended
Acquisitions - Additional Information (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014
Loans At Acquisition Date [Line Items]
Revenues	$8,800,000
Net Income	2,000,000
Acquisition-related due diligence and closing costs	2,681,000	602,000	49,000
Weighted Average amortization period	4 years 3 months 18 days
Depreciation and amortization	61,796,000	54,567,000	51,457,000
1401 K Street, NW [Domain]
Loans At Acquisition Date [Line Items]
Depreciation and amortization				100,000
Impairment of Leasehold				$600,000
Tenant Improvements [Member]
Loans At Acquisition Date [Line Items]
Weighted Average amortization period	4 years 3 months 18 days
In-place Leases [Member]
Loans At Acquisition Date [Line Items]
Weighted Average amortization period	4 years 3 months 18 days
Leasing Commissions [Member]
Loans At Acquisition Date [Line Items]
Weighted Average amortization period	4 years 3 months 18 days
Marketing-Related Intangible Assets [Member]
Loans At Acquisition Date [Line Items]
Weighted Average amortization period	4 years 3 months 18 days
Above Market Leases [Member]
Loans At Acquisition Date [Line Items]
Weighted Average amortization period	4 years 3 months 18 days

Acquisitions_Fair_Value_of_Acq

Acquisitions - Fair Value of Acquired Assets and Liabilities (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Business Combinations [Abstract]
Land	$48,792	$6,458
Acquired tenant improvements	10,857	1,669
Building and improvements	111,173	18,162
In-place leases	12,540	2,886
Acquired leasing commissions	4,681	580
Legal leasing fees	360	2
Above-market leases acquired	2,397	243
Total assets acquired	190,800	30,000
Below-market leases assumed	-2,800	0
Debt assumed	-37,269	0
Net assets acquired	$150,731	$30,000

Acquisitions_Pro_Forma_Financi

Acquisitions - Pro Forma Financial Information (Detail) (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Business Combinations [Abstract]
Pro forma total revenues	$171,686	$170,800
Pro forma net income	$19,461	$5,572
Pro forma net income (loss) per share b basic and diluted	$0.12	($0.12)

Investment_in_Affiliates_Compo

Investment in Affiliates - Components of Investments in Affiliates (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]
Company Investment	$47,482	$49,150
Debt	110,000	105,404
Recourse Debt	2,800	7,000
Prosperity Metro Plaza [Member]
Schedule of Equity Method Investments [Line Items]
Reporting Segment	NorthernB Virginia	Northern Virginia
Ownership Interest	51.00%	51.00%
Company Investment	24,651	24,735
Debt	50,000	48,991
Recourse Debt	0	0
1750 H Street, NW [Member]
Schedule of Equity Method Investments [Line Items]
Reporting Segment	Washington, D.C.	Washington, D.C.
Ownership Interest	50.00%	50.00%
Company Investment	14,834	16,780
Debt	32,000	28,413
Recourse Debt	0	0
Aviation Business Park [Member]
Schedule of Equity Method Investments [Line Items]
Reporting Segment	Maryland	Maryland
Ownership Interest	50.00%	50.00%
Company Investment	5,748	5,008
Debt	0	0
Recourse Debt	0	0
Rivers Park I and II [Member]
Schedule of Equity Method Investments [Line Items]
Reporting Segment	Maryland	Maryland
Ownership Interest	25.00%	25.00%
Company Investment	2,249	2,627
Debt	28,000	28,000
Recourse Debt	$2,800	$7,000

Investment_in_Affiliates_Addit

Investment in Affiliates - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Nov. 12, 2014	Sep. 26, 2014	Mar. 26, 2014	Jul. 10, 2014
	sqft	sqft	sqft	sqft	Rate	Rate	sqft
				Rate	sqft		Rate
Schedule of Equity Method Investments [Line Items]
Long-term Debt	$813,637,000	$673,648,000
Square Feet	8,790,147	9,100,121	13,451,401
Fees from joint ventures	700,000	600,000	500,000
Prosperity Metro Plaza [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Interest				51.00%
Square Feet				327,000
Contractual interest rate				3.91%
Interest only payment date	31-Dec-24
Maturity date of senior notes	1-Dec-29
Joint venture loan prepayment date	1-Jun-29
Rivers Park One And Two [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Interest					25.00%
Square Feet					308,000
Maturity date of senior notes	26-Sep-17
Reduction in variable rate	0.60%
Percentage of outstanding principal					10.00%	25.00%
1750 H Street [Domain]
Schedule of Equity Method Investments [Line Items]
Ownership Interest							50.00%
Square Feet							113,000
Contractual interest rate							3.92%
Maturity date of senior notes	1-Aug-24
Joint venture loan prepayment date	1-Aug-21
Repayment of Long Term Debt [Member] \| Prosperity Metro Plaza [Member]
Schedule of Equity Method Investments [Line Items]
Long-term Debt				48,300,000
Repayment of Long Term Debt [Member] \| 1750 H Street [Domain]
Schedule of Equity Method Investments [Line Items]
Long-term Debt							27,900,000
New Loan [Member] \| Prosperity Metro Plaza [Member]
Schedule of Equity Method Investments [Line Items]
Long-term Debt				50,000,000
New Loan [Member] \| 1750 H Street [Domain]
Schedule of Equity Method Investments [Line Items]
Long-term Debt							32,000,000
Amendment or Modification [Member] \| Rivers Park One And Two [Member]
Schedule of Equity Method Investments [Line Items]
Long-term Debt					28,000,000

Investment_in_Affiliates_Net_A

Investment in Affiliates - Net Assets of Company's Unconsolidated Joint Ventures (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Assets:
Rental property, net	$1,288,873	$1,144,455
Cash and cash equivalents	13,323	8,740	9,374	16,749
Total assets	1,618,460	1,502,460	1,717,748
Liabilities:
Total liabilities	874,223	729,948
Unconsolidated Joint Ventures [Member]
Assets:
Rental property, net	193,533	194,240
Cash and cash equivalents	4,567	3,680
Other assets	16,748	15,585
Total assets	214,848	213,505
Liabilities:
Mortgage loans	110,000	106,384
Other liabilities	7,256	5,046
Total liabilities	117,256	111,430
Net assets	$97,592	$102,075

Investment_in_Affiliates_Resul

Investment in Affiliates - Results of Operations of Company's Unconsolidated Joint Ventures (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Equity Method Investments [Line Items]
Total revenues	$42,928	$40,055	$39,307	$39,363	$37,517	$37,206	$36,915	$37,179	$161,652	$148,815	$142,962
Total operating expenses	-38,595	-36,283	-39,579	-35,744	-33,899	-33,663	-31,221	-32,508	-150,201	-131,289	-126,177
Operating income	4,333	3,772	-272	3,619	3,618	3,543	5,694	4,671	11,451	17,526	16,785
Depreciation and amortization									-61,796	-54,567	-51,457
Interest expense, net									-24,696	-32,803	-40,602
Provision for income taxes									0	0	4,142
Net income									775	-47	40
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Total revenues									23,285	24,017	24,945
Total operating expenses									-7,408	-7,753	-7,377
Operating income									15,877	16,264	17,568
Depreciation and amortization									-9,893	-11,551	-12,564
Interest expense, net									-3,890	-4,222	-4,326
Provision for income taxes									-63	-83	-21
Contingent consideration charge									126	0	0
Net income									$2,157	$408	$657

Notes_Receivable_Summary_of_No

Notes Receivable - Summary of Notes Receivable (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Receivables with Imputed Interest [Line Items]
Face Amount	$63,720	$54,896
Unamortized Origination Fees	-41	-200
Balance	63,679	54,696
Nine Hundered And Fifty Street Nw [Member] \| Notes Receivables Issued on December 2010 [Member]
Receivables with Imputed Interest [Line Items]
Face Amount	34,000	25,000
Unamortized Origination Fees	0	-130
Balance	34,000	24,870
Interest Rate	9.75%	12.50%
America Square [Member] \| Notes Receivables Issued on April 2011 [Member]
Receivables with Imputed Interest [Line Items]
Face Amount	29,720	29,896
Unamortized Origination Fees	-41	-70
Balance	$29,679	$29,826
Interest Rate	9.00%	9.00%

Notes_Receivable_Additional_In

Notes Receivable - Additional Information (Detail) (USD $)	12 Months Ended		0 Months Ended	12 Months Ended		0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Jan. 10, 2014	Dec. 31, 2012	Dec. 31, 2011	Feb. 24, 2015	Apr. 30, 2011	Jan. 27, 2015
	sqft	sqft	Jan. 10, 2014	Dec. 31, 2012	Dec. 31, 2011	Feb. 24, 2015	Apr. 30, 2011	sqft
Receivables with Imputed Interest [Line Items]
Square Feet	8,790,147	9,100,121		13,451,401
Income from amortization of origination fees	$32,000	$100,000
Notes Receivables Issued on April 2011 [Member]
Receivables with Imputed Interest [Line Items]
Notes Receivables Issued Date		1-Apr-11
Notes Receivables Issued on December 2010 [Member]
Receivables with Imputed Interest [Line Items]
Square Feet	287,000
Mezzanine loan provided to owners	25,000,000		34,000,000
Notes Receivables Issued Date	1-Dec-10	1-Dec-10
Maturity date of loan					1-Apr-17
Unsecured revolving credit facility			9,000,000
Interest income	6,100,000	5,900,000		5,900,000
Notes Receivables Issued on December 2010 [Member] \| Maximum [Member]
Receivables with Imputed Interest [Line Items]
Fixed interest rate on loan			12.50%
Notes Receivables Issued on December 2010 [Member] \| Minimum [Member]
Receivables with Imputed Interest [Line Items]
Fixed interest rate on loan			9.75%
America Square [Member]
Receivables with Imputed Interest [Line Items]
Mezzanine loan provided to owners							30,000,000
Maturity date of loan	1-May-16
America Square [Member] \| Notes Receivables Issued on April 2011 [Member]
Receivables with Imputed Interest [Line Items]
Fixed interest rate on loan	9.00%	9.00%
Nine Hundered And Fifty Street Nw [Member]
Receivables with Imputed Interest [Line Items]
Write Off Unamortized Loan Origination Fees	100,000
Nine Hundered And Fifty Street Nw [Member] \| Notes Receivables Issued on December 2010 [Member]
Receivables with Imputed Interest [Line Items]
Fixed interest rate on loan	9.75%	12.50%
Subsequent Event [Member] \| America Square [Member]
Receivables with Imputed Interest [Line Items]
Square Feet								461,000
Mezzanine loan provided to owners						29,700,000
Prepayment Fee Income						2,400,000
Subsequent Event [Member] \| Loans Receivable Payment Receipt [Member] \| America Square [Member]
Receivables with Imputed Interest [Line Items]
Mezzanine loan provided to owners						$29,700,000

Intangible_Assets_Intangible_A

Intangible Assets - Intangible Assets and Deferred Market Rent Liabilities (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Intangible Assets By Major Class [Line Items]
Deferred market rent liability, Net Intangibles	$2,827	$1,522
All Properties, Including Held for Sale [Member]
Intangible Assets By Major Class [Line Items]
Gross Intangibles	74,712	63,122
Accumulated Amortization	-28,796	-24,226
Net Intangibles	45,916	38,896
Goodwill	6,930	6,930
Deferred market rent liability, Gross Intangible	5,193	4,381
Deferred market rent liability, Accumulated Amortization	-2,348	-2,767
Deferred market rent liability, Net Intangibles	2,845	1,614
All Properties, Including Held for Sale [Member] \| In-place Leases [Member]
Intangible Assets By Major Class [Line Items]
Gross Intangibles	51,258	44,772
Accumulated Amortization	-22,443	-18,843
Net Intangibles	28,815	25,929
All Properties, Including Held for Sale [Member] \| Customer Relationships [Member]
Intangible Assets By Major Class [Line Items]
Gross Intangibles	906	1,002
Accumulated Amortization	-654	-591
Net Intangibles	252	411
All Properties, Including Held for Sale [Member] \| Leasing Commissions [Member]
Intangible Assets By Major Class [Line Items]
Gross Intangibles	11,335	7,796
Accumulated Amortization	-4,272	-3,361
Net Intangibles	7,063	4,435
All Properties, Including Held for Sale [Member] \| Legal Fees [Member]
Intangible Assets By Major Class [Line Items]
Gross Intangibles	377	137
Accumulated Amortization	-118	-83
Net Intangibles	259	54
All Properties, Including Held for Sale [Member] \| Deferred Market Rent Assets [Member]
Intangible Assets By Major Class [Line Items]
Gross Intangibles	3,906	2,485
Accumulated Amortization	-1,309	-1,348
Net Intangibles	$2,597	$1,137

Intangible_Assets_Additional_I

Intangible Assets - Additional Information (Detail) (USD $)	12 Months Ended
Intangible Assets - Additional Information (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$10,300,000	$8,300,000	$10,700,000
Additional rental revenue	14,000
Reduction in rental revenue	100,000	200,000
Losses due to termination of tenant leases and defaults	$1,100,000	$1,000,000	$1,100,000

Intangible_Assets_Projected_Ne

Intangible Assets - Projected Net Amortization of Intangible Assets and Deferred Market Liabilities Including Amounts from Properties Classified as Held-For-Sale (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
2015	$10,747
2016	8,745
2017	4,275
2018	2,707
2019	2,393
Thereafter	7,274
Total	$36,141

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
Income Taxes - Additional Information (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Real Estate Acquired Through Foreclosure Under Forward Purchase Agreements [Line Items]
Franchise taxes effective rate	0.00%	9.98%
Provision for income taxes		$0	$0	$4,142,000
Deferred tax assets		0	0
Deferred tax liabilities		0	0
Accounts and Other Receivables [Member]
Real Estate Acquired Through Foreclosure Under Forward Purchase Agreements [Line Items]
Tax refund receivable		$1,000,000	$1,000,000

Dispositions_Summary_of_Comple

Dispositions - Summary of Completed Property Dispositions within Continuing Operations(Detail) (USD $)	12 Months Ended	0 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Oct. 16, 2014	Jun. 26, 2014	Dec. 31, 2013	Dec. 31, 2012
	sqft	Oct. 16, 2014	Jun. 26, 2014	sqft	sqft
Schedule Of Discontinued Operations [Line Items]
Property Type	Office
Square Feet	8,790,147			9,100,121	13,451,401
Northern Virginia Reporting Segment [Member]
Schedule Of Discontinued Operations [Line Items]
Square Feet	167,000
Owings Mills Business Park [Domain] \| MARYLAND [Member]
Schedule Of Discontinued Operations [Line Items]
Reporting Segment	Maryland
Disposition Date	16-Oct-14
Property Type	Business Park
Square Feet		180,475
Net Sale Proceeds		$12,417
Corporate Campus at Ashburn Center [Member] \| Northern Virginia Reporting Segment [Member]
Schedule Of Discontinued Operations [Line Items]
Reporting Segment	Northern Virginia
Disposition Date	26-Jun-14
Property Type	Business Park
Square Feet			194,184
Net Sale Proceeds			$39,910

Dispositions_Disposed_or_Heldf

Dispositions - Disposed or Held-for-Sale Properties within Continuing Operations (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues	$7,688	$31,654	$50,985
Property operating expenses	-3,612	-10,564	-16,226
Depreciation and amortization	-3,662	-8,937	-14,958
Interest expense, net of interest income	-268	-1,268	-2,947
Impairment of rental property	0	-4,092	-1,072
(Loss) income from operations of disposed property	146	6,793	15,782
Loss on debt extinguishment	0	-4,414	0
Continuing Operations [Member] \| Corporate Campus at Ashburn Center and Owings Mills Business Park [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues	2,920	5,223	5,363
Property operating expenses	-1,172	-1,521	-1,375
Depreciation and amortization	-1,047	-1,424	-1,517
Interest expense, net of interest income	0	0	-230
Impairment of rental property	-3,956	0	-3,246
(Loss) income from operations of disposed property	-3,255	2,278	-1,005
Loss on debt extinguishment	0	0	-466
Gain on sale of rental property	21,230	0	0
Net income (loss) from continuing operations	$17,975	$2,278	($1,471)

Dispositions_Additional_Inform

Dispositions - Additional Information (Detail) (USD $)	12 Months Ended		0 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Feb. 09, 2015	Oct. 16, 2014	Dec. 31, 2013		Dec. 31, 2012
	Interger				sqft		sqft
	sqft
Schedule Of Discontinued Operations [Line Items]
Square Feet	8,790,147				9,100,121		13,451,401
Land and land improvements	$325,214				$287,015
Buildings and improvements	949,683				807,198
Tenant improvements	159,867				138,543
Construction in process	69,181				93,174
Real Estate Investment Property, Accumulated Depreciation	215,499				185,725
Mortgage Loans Payable	308,637	[1]		22,000	274,648	[1]
Richmond [Member]
Schedule Of Discontinued Operations [Line Items]
Number of Buildings Held-For-Sale	19
Square Feet	827,900
Land and land improvements	7,700
Buildings and improvements	62,000
Tenant improvements	8,500
Construction in process	100
Real Estate Investment Property, Accumulated Depreciation	20,600
Other assets	2,000
Mortgage Loans Payable	3,498				4,481
Other liabilities	1,100
Properties Held for Sale [Member]
Schedule Of Discontinued Operations [Line Items]
Land and land improvements					21,400
Buildings and improvements					97,500
Tenant improvements					12,800
Construction in process					100
Real Estate Investment Property, Accumulated Depreciation					29,400
Other assets					4,100
Mortgage Loans Payable					4,500
Other liabilities					$1,000
Subsequent Event [Member] \| Richmond [Member]
Schedule Of Discontinued Operations [Line Items]
Effective Date of Richmond PSA Sale			9-Feb-15

[1]	At DecemberB 31, 2014, LIBOR was 0.17%. All references to LIBOR in the consolidated financial statements refer to one-month LIBOR.

Dispositions_Summary_of_Comple1

Dispositions - Summary of Completed and Anticipated Property Dispositions within Discontinued Operations (Detail) (USD $)	0 Months Ended	3 Months Ended	12 Months Ended			1 Months Ended	0 Months Ended
In Thousands, unless otherwise specified	Jun. 18, 2013	Jun. 30, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Nov. 30, 2012	7-May-13	Feb. 09, 2015
	Property	Property	sqft	sqft	sqft	Buildings	sqft	Feb. 09, 2015
Schedule Of Discontinued Operations [Line Items]
Property Type			Office
Square Feet			8,790,147	9,100,121	13,451,401
Net Sale Proceeds			$97,701	$263,469	$14,341
Number of industrial properties company sold		24
Number Of Remaining Industrial Properties Sold	23
Richmond [Member]
Schedule Of Discontinued Operations [Line Items]
Reporting Segment			Southern Virginia
Property Type			Business Park
Square Feet			827,900
Patrick Center [Member]
Schedule Of Discontinued Operations [Line Items]
Reporting Segment			Maryland
Disposition Date			16-Apr-14
Property Type			Office
Square Feet			66,269
Net Sale Proceeds			10,888
West Park [Member]
Schedule Of Discontinued Operations [Line Items]
Reporting Segment			Maryland
Disposition Date			2-Apr-14
Property Type			Office
Square Feet			28,333
Net Sale Proceeds			2,871
Girard Business Center and Gateway Center [Member]
Schedule Of Discontinued Operations [Line Items]
Reporting Segment			Maryland
Disposition Date			29-Jan-14
Property Type			BusinessB ParkB andB Office
Square Feet			341,973
Net Sale Proceeds			31,616
Worman's Mill Court [Member]
Schedule Of Discontinued Operations [Line Items]
Reporting Segment			Maryland
Disposition Date			19-Nov-13
Property Type			Office
Square Feet			40,099
Net Sale Proceeds			3,362
Triangle Business Center [Member]
Schedule Of Discontinued Operations [Line Items]
Reporting Segment			Maryland
Disposition Date			27-Sep-13
Property Type			Business Park
Square Feet			74,429
Net Sale Proceeds			2,732
4200 Tech Court [Member]
Schedule Of Discontinued Operations [Line Items]
Reporting Segment			NorthernB Virginia
Disposition Date			15-Aug-13
Property Type			Office
Square Feet			33,875
Net Sale Proceeds			3,210
Industrial Portfolio [Member]
Schedule Of Discontinued Operations [Line Items]
Reporting Segment			Various
Disposal Date Of Property			May/JuneB 2013
Property Type			Industrial
Square Feet			4,280,985
Net Sale Proceeds			176,569
4212 Tech Court [Member]
Schedule Of Discontinued Operations [Line Items]
Reporting Segment			NorthernB Virginia
Disposition Date			5-Jun-13
Property Type			Office
Square Feet			32,055
Net Sale Proceeds			2,469
Owings Mills Business Park [Member]
Schedule Of Discontinued Operations [Line Items]
Reporting Segment			Maryland
Disposition Date			7-Nov-12
Property Type			Business Park
Square Feet			38,779
Net Sale Proceeds			3,472
Number of building sold						2
Number of buildings						6
Goldenrod Lane [Member]
Schedule Of Discontinued Operations [Line Items]
Reporting Segment			Maryland
Disposition Date			31-May-12
Property Type			Office
Square Feet			23,518
Net Sale Proceeds			2,663
Woodlands Business Center [Member]
Schedule Of Discontinued Operations [Line Items]
Reporting Segment			Maryland
Disposition Date			8-May-12
Property Type			Office
Square Feet			37,887
Net Sale Proceeds			2,885
Airpark Place Business Center [Member]
Schedule Of Discontinued Operations [Line Items]
Reporting Segment			Maryland
Disposition Date			22-Mar-12
Property Type			Business Park
Square Feet			82,429
Net Sale Proceeds			$5,153
Haymarket [Member] \| Virginia [Member]
Schedule Of Discontinued Operations [Line Items]
Reporting segment included in company's industrial properties							236,000
Subsequent Event [Member] \| Richmond [Member]
Schedule Of Discontinued Operations [Line Items]
Effective Date of Richmond PSA Sale								9-Feb-15

Dispositions_Net_Income_from_D

Dispositions - Net Income from Discontinued Operations (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Discontinued Operations and Disposal Groups [Abstract]
Revenues	$7,688	$31,654	$50,985
Property operating expenses	-3,612	-10,564	-16,226
Depreciation and amortization	-3,662	-8,937	-14,958
Interest expense, net of interest income	-268	-1,268	-2,947
Impairment of rental property	0	-4,092	-1,072
(Loss) income from operations of disposed property	146	6,793	15,782
Loss on debt extinguishment	0	-4,414	0
Gain on sale of real estate property	1,338	19,363	161
Net income from discontinued operations	$1,484	$21,742	$15,943

Debt_Schedule_of_Borrowings_De

Debt - Schedule of Borrowings (Detail) (USD $)	Dec. 31, 2014		Oct. 16, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	Dec. 31, 2014		Oct. 16, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Mortgage Loans Payable	$308,637	[1]	$22,000	$274,648	[1]
Unsecured revolving credit facility, effective interest rate of LIBOR plus 1.50%, maturing October 2017	205,000	[1]		99,000	[1]
Long-term Debt	813,637			673,648
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 [Member]
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	$300,000			$300,000

[1]	At DecemberB 31, 2014, LIBOR was 0.17%. All references to LIBOR in the consolidated financial statements refer to one-month LIBOR.

Debt_Schedule_of_Borrowings_2_

Debt - Schedule of Borrowings 2 (Detail) (USD $)	0 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Oct. 16, 2014	Dec. 31, 2014		Oct. 16, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Effective interest rate on the notes		4.75%	[1]
Effective interest rate on secured term loan	2.50%	1.70%
Debt instrument variable rate basis		0.17%
Mortgage Loans Payable	$22,000	$308,637	[2]	$22,000	$274,648	[2]
Mortgage Loans [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, effective percentage rate range, minimum		4.40%
Debt instrument, interest rate, effective percentage rate range, maximum		6.63%
Debt instrument maturity date		Jun-23
Unsecured Term Loan, Effective Interest Rates Ranging from LIBOR Plus 1.45% to LIBOR Plus 1.90%, with Staggered Maturity Dates ranging from October 2018 to October 2020 [Member]
Debt Instrument [Line Items]
Debt instrument basis spread on variable rate, minimum		1.65%
Debt instrument basis spread on variable rate, maximum		2.05%
Debt instrument maturity date		October 2018 to October 2020
Unsecured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Effective interest rate on the notes		1.70%
Debt instrument maturity date		Oct-17
Richmond [Member]
Debt Instrument [Line Items]
Mortgage Loans Payable		3,498			4,481
Properties Held for Sale [Member]
Debt Instrument [Line Items]
Mortgage Loans Payable					$4,500

[1]	Weighted average interest rate on total mortgage debt.
[2]	At DecemberB 31, 2014, LIBOR was 0.17%. All references to LIBOR in the consolidated financial statements refer to one-month LIBOR.

Debt_Summary_of_Companys_Mortg

Debt - Summary of Company's Mortgage Debt (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Oct. 16, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Effective Interest Rate	4.75%	[1]
Total Mortgage Debt	$308,637	[2]	$22,000	$274,648	[2]
Unamortized fair value adjustments	-443
Total contractual principal balance	813,637			673,648
Mortgage Loans [Member]
Debt Instrument [Line Items]
Total contractual principal balance	308,194			273,985
Annapolis Business Center [Member]
Debt Instrument [Line Items]
Contractual interest rate	5.74%
Effective Interest Rate	6.25%
Maturity Date	Jun-14
Total Mortgage Debt	0			8,076
Jackson National Life Loan [Member]
Debt Instrument [Line Items]
Contractual interest rate	5.19%
Effective Interest Rate	5.19%
Maturity Date	Aug-15
Total Mortgage Debt	64,943			66,116
440 First Street, NW Construction Loan [Member]
Debt Instrument [Line Items]
Contractual interest rate	2.50%
Contractual Interest Rate terms	LIBORB +B 2.50%
Effective Interest Rate	2.67%
Maturity Date	May-16
Total Mortgage Debt	32,216			21,699
Storey Park [Member]
Debt Instrument [Line Items]
Contractual interest rate	2.50%
Contractual Interest Rate terms	LIBORB +B 2.50%
Effective Interest Rate	2.67%
Maturity Date	Oct-16
Total Mortgage Debt	22,000			22,000
Gateway Centre Manassas Building I [Member]
Debt Instrument [Line Items]
Contractual interest rate	7.35%
Effective Interest Rate	5.88%
Maturity Date	NovemberB 2016
Total Mortgage Debt	432			638
Hillside I and II [Member]
Debt Instrument [Line Items]
Contractual interest rate	5.75%
Effective Interest Rate	4.62%
Maturity Date	DecemberB 2016
Total Mortgage Debt	12,949			13,349
Redland Corporate Center Buildings II & III [Member]
Debt Instrument [Line Items]
Contractual interest rate	4.20%
Effective Interest Rate	4.64%
Maturity Date	Nov-17
Total Mortgage Debt	65,816			67,038
840 First Street, NE / 500 First Street, NW [Member]
Debt Instrument [Line Items]
Contractual interest rate	5.72%
Effective Interest Rate	6.01%
Maturity Date	Jul-20
Total Mortgage Debt	36,539			37,151
Battlefield Corporate Center [Member]
Debt Instrument [Line Items]
Contractual interest rate	4.26%
Effective Interest Rate	4.40%
Maturity Date	Nov-20
Total Mortgage Debt	3,692			3,851
Airpark Business Center [Member]
Debt Instrument [Line Items]
Contractual interest rate	7.45%
Effective Interest Rate	6.63%
Maturity Date	Jun-21
Total Mortgage Debt	913			1,022
1211 Connecticut Avenue, NW [Member]
Debt Instrument [Line Items]
Contractual interest rate	4.22%
Effective Interest Rate	4.47%
Maturity Date	Jul-22
Total Mortgage Debt	29,691			30,249
1401 K Street, NW [Member]
Debt Instrument [Line Items]
Contractual interest rate	4.80%
Effective Interest Rate	4.93%
Maturity Date	Jun-23
Total Mortgage Debt	36,861			0
Continuing Operations Properties [Member]
Debt Instrument [Line Items]
Total Mortgage Debt	305,139			270,167
Unamortized fair value adjustments	-370			-554
Continuing Operations Properties [Member] \| Mortgage Loans [Member]
Debt Instrument [Line Items]
Total contractual principal balance	304,769			269,613
Hanover Business Center [Member]
Debt Instrument [Line Items]
Contractual interest rate	8.88%
Effective Interest Rate	6.63%
Maturity Date	Aug-15
Total Mortgage Debt	104			252
Chesterfield Business Center [Member]
Debt Instrument [Line Items]
Contractual interest rate	8.50%
Effective Interest Rate	6.63%
Maturity Date	Sep-15
Total Mortgage Debt	302			681
Hanonver Business Building C [Member]
Debt Instrument [Line Items]
Contractual interest rate	7.88%
Effective Interest Rate	6.63%
Maturity Date	Dec-17
Total Mortgage Debt	505			653
Chesterfield Business Center Bldg ABEF [Member]
Debt Instrument [Line Items]
Contractual interest rate	7.45%
Effective Interest Rate	6.63%
Maturity Date	Jun-21
Total Mortgage Debt	1,674			1,873
Richmond [Member]
Debt Instrument [Line Items]
Total Mortgage Debt	3,498			4,481
Unamortized fair value adjustments	73			109
Total contractual principal balance	$3,425			$4,372

[1]	Weighted average interest rate on total mortgage debt.
[2]	At DecemberB 31, 2014, LIBOR was 0.17%. All references to LIBOR in the consolidated financial statements refer to one-month LIBOR.

Debt_Summary_of_Companys_Mortg1

Debt - Summary of Company's Mortgage Debt 2 (Detail) (USD $)	0 Months Ended	3 Months Ended	12 Months Ended
	Oct. 16, 2014	Sep. 30, 2013	Dec. 31, 2014		Dec. 31, 2014		Oct. 16, 2014	Dec. 31, 2013
Debt Disclosure [Abstract]
Debt instrument variable rate basis			0.17%		0.17%
Amount borrowed		$21,700,000			$10,500,000
Ownership Interest In Joint Venture			97.00%		97.00%
Mortgage Loans Payable			$308,637,000	[1]	$308,637,000	[1]	$22,000,000	$274,648,000	[1]
Debt Instrument, Basis Spread on Variable Rate	2.50%		2.50%		1.70%
Debt Instrument Maturity Extension Period			1 year		1 year

[1]	At DecemberB 31, 2014, LIBOR was 0.17%. All references to LIBOR in the consolidated financial statements refer to one-month LIBOR.

Debt_Additional_Information_De

Debt - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended	12 Months Ended		1 Months Ended
	Oct. 16, 2014	Sep. 30, 2013	Dec. 31, 2014		31-May-16	Dec. 31, 2013		Sep. 30, 2014	Aug. 04, 2011	Jun. 05, 2013
			Rate						Rate
			Property
Debt Instrument [Line Items]
Mortgage Loans on Real Estate			$37,300,000
Mortgage Loans Payable	22,000,000		308,637,000	[1]		274,648,000	[1]
Debt Instrument, Basis Spread on Variable Rate	2.50%		1.70%
Long-term Debt			813,637,000			673,648,000
Amount borrowed		21,700,000	10,500,000
Maturity Period			1 year
Number of consolidated properties that secured mortgage debt			18
Greyhound Property [Member]
Debt Instrument [Line Items]
Percentage Of Interest In Joint Venture Owned By Entity									97.00%
Mortgage Loans on Real Estate	22,000,000
Contractual interest rate								5.00%
Debt Instrument, Basis Spread on Variable Rate	2.50%
Maturity date of senior notes			16-Oct-16
Long-term Debt	6,000,000
440 First Street, NW [Member]
Debt Instrument [Line Items]
Borrowing capacity of a construction loan										43,500,000
Amount borrowed			$10,500,000
Maturity Period			1 year
Percentage of outstanding principal			50.00%
Subsequent Event [Member] \| 440 First Street, NW [Member]
Debt Instrument [Line Items]
Maturity date of senior notes					30-May-16

[1]	At DecemberB 31, 2014, LIBOR was 0.17%. All references to LIBOR in the consolidated financial statements refer to one-month LIBOR.

Debt_Originated_or_Assumed_Mor

Debt - Originated or Assumed Mortgages (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014
Debt Instrument [Line Items]
Effective Interest Rate	4.75%	[1]
Storey Park [Member]
Debt Instrument [Line Items]
Month	October
Year	2014
Contractual Interest Rate terms	LIBOR + 2.50%
Effective Interest Rate	5.80%
Principal Amount	$22,000	[2]
1401 K Street, NW [Member]
Debt Instrument [Line Items]
Month	April
Year	2014
Effective Interest Rate	4.93%
Principal Amount	37,269	[2]
440 First Street, NW Construction Loan [Member]
Debt Instrument [Line Items]
Month	June
Year	2013
Effective Interest Rate	5.00%
Principal Amount	$21,699	[2]

[1]	Weighted average interest rate on total mortgage debt.
[2]	We have a 97% ownership interest in the property through a consolidated joint venture. The loan balance in the chart above reflects the entire loan balance, which is reflected in our consolidated balance sheets.

Debt_Originated_or_Assumed_Mor1

Debt - Originated or Assumed Mortgages 2 (Detail) (USD $)	3 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2014	Aug. 04, 2011
	Sep. 30, 2013	Dec. 31, 2014	Rate
Debt Instrument [Line Items]
Amount borrowed	$21.70	$10.50
Storey Park [Member]
Debt Instrument [Line Items]
Percentage Of Interest In Joint Venture Owned By Entity			97.00%
440 First Street, NW Construction Loan [Member]
Debt Instrument [Line Items]
Percentage of outstanding principal		50.00%

Debt_Repayment_of_Mortgages_De

Debt - Repayment of Mortgages (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014
Debt Instrument [Line Items]
Effective Interest Rate	4.75%	[1]
Storey Park [Member]
Debt Instrument [Line Items]
Month	October
Year	2014
Effective Interest Rate	5.80%
Principal Balance Repaid	$22,000
Annapolis Business Center [Member]
Debt Instrument [Line Items]
Month	May
Year	2014
Effective Interest Rate	6.25%
Principal Balance Repaid	8,027
840 First Street, NE [Member]
Debt Instrument [Line Items]
Month	September
Year	2013
Effective Interest Rate	6.05%
Principal Balance Repaid	53,877
Linden Business Center [Member]
Debt Instrument [Line Items]
Month	September
Year	2013
Effective Interest Rate	5.58%
Principal Balance Repaid	6,622
Cloverleaf Center [Member]
Debt Instrument [Line Items]
Month	June
Year	2013
Effective Interest Rate	6.75%
Principal Balance Repaid	16,427
Mercedes Center - Note 1 [Member]
Debt Instrument [Line Items]
Month	June
Year	2013
Effective Interest Rate	6.04%
Principal Balance Repaid	4,799
Mercedes Center - Note 2 [Member]
Debt Instrument [Line Items]
Month	June
Year	2013
Effective Interest Rate	6.30%
Principal Balance Repaid	9,260
1434 Crossways Blvd Building I [Member]
Debt Instrument [Line Items]
Month	February
Year	2013
Effective Interest Rate	5.38%
Principal Balance Repaid	7,597
Ten Three Twenty [Member]
Debt Instrument [Line Items]
Month	February
Year	2013
Effective Interest Rate	7.29%
Principal Balance Repaid	13,273
Cedar Hill [Member]
Debt Instrument [Line Items]
Month	February
Year	2013
Effective Interest Rate	6.58%
Principal Balance Repaid	15,364
Prosperity Business Center [Member]
Debt Instrument [Line Items]
Month	January
Year	2013
Effective Interest Rate	5.75%
Principal Balance Repaid	3,242
Northbridge [Member] \| Jackson National Life Loan [Member]
Debt Instrument [Line Items]
Month	June
Year	2013
Effective Interest Rate	5.19%
Principal Balance Repaid	6,985
I-66 Commerce Center [Member] \| Jackson National Life Loan [Member]
Debt Instrument [Line Items]
Month	May
Year	2013
Effective Interest Rate	5.19%
Principal Balance Repaid	$21,695

[1]	Weighted average interest rate on total mortgage debt.

Debt_Repayment_of_Mortgages_2_

Debt - Repayment of Mortgages 2 (Detail) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013
840 First Street, NE [Member]
Debt Instrument [Line Items]
Mortgage loan encumbered	$53.90
Maturity date of senior notes	1-Oct-13
500 First Street, NW [Member]
Debt Instrument [Line Items]
Mortgage loan encumbered	$37.30

Debt_Unsecured_Term_Loan_Detai

Debt - Unsecured Term Loan (Detail) (USD $)	0 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Oct. 16, 2014	Dec. 31, 2014		Dec. 31, 2013
Debt Instrument [Line Items]
Amount		$300,000		$300,000
Debt Instrument, Basis Spread on Variable Rate	2.50%	1.70%
Tranche A [Member]
Debt Instrument [Line Items]
Maturity Date		Oct-18
Amount		100,000
Interest Rate		LIBOR, plus 165 basis points	[1]
Debt Instrument, Basis Spread on Variable Rate		1.65%
Tranche B [Member]
Debt Instrument [Line Items]
Maturity Date		Oct-19
Amount		100,000
Interest Rate		LIBOR, plus 180 basis points	[1]
Debt Instrument, Basis Spread on Variable Rate		1.80%
Tranche C [Member]
Debt Instrument [Line Items]
Maturity Date		OctoberB 2020
Amount		100,000
Interest Rate		LIBOR,B plusB 205B basisB points	[1]
Debt Instrument, Basis Spread on Variable Rate		2.05%
Term Loan [Member]
Debt Instrument [Line Items]
Amount		$300,000

[1]	At DecemberB 31, 2014, LIBOR was 0.17%. The interest rate spread is subject to change based on our maximum total indebtedness ratio. For more information, see note 11(e) Debt b Financial Covenants.

Debt_Additional_Information_1_

Debt - Additional Information 1 (Detail) (USD $)	0 Months Ended	12 Months Ended
	Oct. 16, 2014	Dec. 31, 2014	Dec. 31, 2013	Jan. 31, 2014
	Oct. 16, 2014	Derivative	Dec. 31, 2013	Jan. 31, 2014
Debt Instrument [Line Items]
Weighted average borrowings outstanding on unsecured revolving credit facility		$136,100,000	$139,400,000
Weighted average interest rate		1.70%	2.60%
Maximum outstanding borrowings		216,000,000	245,000,000
Debt instrument variable rate basis		0.17%
Unsecured revolving credit facility		205,000,000
Debt Instrument, Basis Spread on Variable Rate	2.50%	2.50%
Weighted average interest rate		1.90%
Available capacity on the unsecured revolving credit facility		79,000,000
Annual commitment fee		0.25%
Number of interest rate swap agreements		11
Interest Rate Swap [Member]
Debt Instrument [Line Items]
Fixed effective interest rate		1.51%
Amount on variable rate debt		$300,000,000		$50,000,000

Debt_Aggregate_Debt_Maturities

Debt - Aggregate Debt Maturities (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Debt Disclosure [Abstract]
2015	$69,553
2016	70,763
2017	270,999
2018	102,746
2019	102,894
Thereafter	196,239
Long term debt before unamortized discount	813,194
Unamortized fair value adjustments	443
Total contractual principal balance	$813,637	$673,648

Derivative_Instruments_Additio

Derivative Instruments - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 31, 2014
Derivatives, Fair Value [Line Items]
Number of interest rate swap agreements	11
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Fixed effective interest rate	1.51%
Weighted average rate amount on variable rate debt	$300,000,000			$50,000,000
Interest Rate Swap [Member] \| Interest Expense [Member]
Derivatives, Fair Value [Line Items]
Accumulated other comprehensive loss reclassified as an increase in interest expense	4,100,000	4,600,000	4,200,000
Estimated accumulated other comprehensive loss reclassified as an increase in interest expense over the following twelve months	$3,300,000

Derivative_Instruments_Summary

Derivative Instruments - Summary of Interest Rate Swap Agreements (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Jan. 31, 2014
Interest Rate Swap One [Member]
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-16
Notional Amount	$35,000
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	1.75%
Interest Rate Swap Two [Member]
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-16
Notional Amount	25,000
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	1.76%
Interest Rate Swap Three [Member]
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-17
Notional Amount	30,000
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	2.09%
Interest Rate Swap Four [Member]
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-17
Notional Amount	30,000
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	2.09%
Interest Rate Swap Five [Member]
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-18
Notional Amount	30,000
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	1.66%
Interest Rate Swap Six [Member]
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-18
Notional Amount	25,000
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	1.39%
Interest Rate Swap Seven[Member]
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-17
Notional Amount	25,000
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	1.13%
Interest Rate Swap Eight [Member]
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-17
Notional Amount	12,500
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	1.13%
Interest Rate Swap Nine [Member]
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-18
Notional Amount	12,500
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	1.38%
Interest Rate Swap Ten [Member]
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-17
Notional Amount	50,000
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	0.96%
Interest Rate Swap Eleven [Member]
Derivatives, Fair Value [Line Items]
Maturity Date	31-Jul-18
Notional Amount	25,000
Interest Rate Contractual Component	LIBOR
Fixed LIBOR Interest Rate	1.14%
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	$300,000	$50,000
Fixed LIBOR Interest Rate	1.51%

Fair_Value_Measurements_Fair_V

Fair Value Measurements - Fair Value of Assets and Liabilities (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value Measurements, Non-recurring [Member]
Non-recurring Measurements:
Impaired real estate assets		$2,909
Fair Value Measurements, Recurring [Member]
Recurring Measurements:
Derivative instrument-swap assets	133	551
Derivative instrument-swap liabilities	3,569	4,576
Fair Value, Inputs, Level 1 [Member] \| Fair Value Measurements, Non-recurring [Member]
Non-recurring Measurements:
Impaired real estate assets		0
Fair Value, Inputs, Level 1 [Member] \| Fair Value Measurements, Recurring [Member]
Recurring Measurements:
Derivative instrument-swap assets	0	0
Derivative instrument-swap liabilities	0	0
Level 2 [Member] \| Fair Value Measurements, Non-recurring [Member]
Non-recurring Measurements:
Impaired real estate assets		2,909
Level 2 [Member] \| Fair Value Measurements, Recurring [Member]
Recurring Measurements:
Derivative instrument-swap assets	133	551
Derivative instrument-swap liabilities	3,569	4,576
Level 3 [Member] \| Fair Value Measurements, Non-recurring [Member]
Non-recurring Measurements:
Impaired real estate assets		0
Level 3 [Member] \| Fair Value Measurements, Recurring [Member]
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	12 Months Ended			3 Months Ended
	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013	Mar. 31, 2012
		Buildings
		Derivative
Derivatives, Fair Value [Line Items]
Contingent Consideration Obligations Fair Value Disclosure			$39,000		$39,000
Number Of Common Operating Partnership Units Issued For Additional Space Purchased	3,125		6,718
Impairment charges		3,956,000	0	2,444,000
Number of buildings sold		4
Impairment of real estate assets		4,000,000	4,100,000	3,500,000
Number of interest rate swap agreements		11
West Park [Member]
Derivatives, Fair Value [Line Items]
Impairment charges					2,200,000
Owings Mills Business Park [Member]
Derivatives, Fair Value [Line Items]
Impairment of real estate assets		4,000,000
Impairment charge on property						2,400,000
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Variable rate debt hedged		$300,000,000
Minimum number of daily snapshot used for valuation of interest rate swap agreements		7,500

Fair_Value_Measurements_Fair_V1

Fair Value Measurements - Fair Value of Debt Instruments (Detail) (USD $)	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Apr. 30, 2011	Feb. 24, 2015	Jan. 27, 2015
	sqft		sqft		sqft	Apr. 30, 2011	Feb. 24, 2015	sqft
Financial Assets:
Carrying value of notes receivable	$63,679,000		$54,696,000
Financial Liabilities:
Square Feet	8,790,147		9,100,121		13,451,401
Mezzanine Properties [Member]
Financial Assets:
Fair value of notes receivable	63,700,000		54,900,000
America Square [Member]
Financial Liabilities:
Mezzanine loan provided to owners						30,000,000
Reported Value Measurement [Member]
Financial Assets:
Carrying value of notes receivable	63,679,000	[1]	54,696,000	[1]
Financial Liabilities:
Carrying value of the debt instruments	813,637,000		673,648,000
Reported Value Measurement [Member] \| Mortgage Debt [Member]
Financial Liabilities:
Carrying value of the debt instruments	308,637,000		274,648,000
Reported Value Measurement [Member] \| Unsecured Debt [Member]
Financial Liabilities:
Carrying value of the debt instruments	300,000,000		300,000,000
Reported Value Measurement [Member] \| Unsecured Revolving Credit Facility [Member]
Financial Liabilities:
Carrying value of the debt instruments	205,000,000		99,000,000
Estimate of Fair Value Measurement [Member]
Financial Assets:
Fair value of notes receivable	63,720,000	[1]	56,812,000	[1]
Financial Liabilities:
Fair value of the debt instruments	797,882,000		661,873,000
Estimate of Fair Value Measurement [Member] \| Mortgage Debt [Member]
Financial Liabilities:
Fair value of the debt instruments	292,882,000		262,873,000
Estimate of Fair Value Measurement [Member] \| Unsecured Debt [Member]
Financial Liabilities:
Fair value of the debt instruments	300,000,000		300,000,000
Estimate of Fair Value Measurement [Member] \| Unsecured Revolving Credit Facility [Member]
Financial Liabilities:
Fair value of the debt instruments	205,000,000		99,000,000
Subsequent Event [Member] \| America Square [Member]
Financial Liabilities:
Square Feet								461,000
Mezzanine loan provided to owners							$29,700,000

[1]	The principal amount of our notes receivable was $63.7 million and $54.9 million at DecemberB 31, 2014 and 2013, respectively. On January 27, 2015, the owners of Americabs Square, a 461,000 square foot office complex located in Washington, D.C., gave notice of their intent to prepay, on or about February 24, 2015, a mezzanine loan, which has an outstanding $29.7 million balance of the $30.0 million mezzanine loan that we provided them in April 2011.

Commitments_and_Contingencies_1

Commitments and Contingencies - Summary of Operating Leases Generating Future Minimum Rental Payments (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Future minimum rents, 2015	$133,834
Future minimum rents, 2016	127,967
Future minimum rents, 2017	104,975
Future minimum rents, 2018	90,376
Future minimum rents, 2019	76,520
Future minimum rents, Thereafter	214,378
Future minimum rents, Total	$748,050

Commitments_and_Contingencies_2

Commitments and Contingencies - Additional Information (Detail) (USD $)	3 Months Ended					12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	sqft	sqft	Tenants	sqft	sqft	sqft
	Person		sqft			Person
Operating Leases [Abstract]
Occupancy rate in the Company's consolidated properties	87.90%					87.90%
Number of tenants in the company's consolidated rental properties	582					582
Square Footage In Development Or Redevelopment	200,000					200,000
Expansion Of Corporate Space					19,000
Allowance Receivable In Future For Tenant Improvement					$1.30
Lease expiration date						31-Jan-21
Lease Agreement Real Estate Property				6,000
Agreement Expiration Date	31-Dec-14
Area Of Sublease Space			5,000
Number Of Tenants Related To Subleasing Of Former Corporate Office Space			1
Lease agreement commence date		1-Jan-13
Additional Area Of Sublease Space		2,700
Subtenant expansion occupancy date						7-Mar-14
Subtenant Lease Expiration Date						31-Jan-18
Subtenant Termination Option Date						21-Jan-16
Corporate Office Leases Rent Expense						1.8	1.8	1.4
Longterm Purchase Commitment Time Period Milestones						5 years
Contingent Consideration [Abstract]
Contingent Liability Upon Default On Development Projects	2.6					2.6
1211 Connecticut Avenue, NW [Member]
Operating Leases [Abstract]
Lease Agreement Real Estate Property	4,900
440 First Street, NW [Member]
Contingent Consideration [Abstract]
Amount Accrued Outstanding Related To Redevelopment Activities	1.4					1.4
Debt Instrument Collateralized Debt Obligations Amount	$11.80					$11.80

Commitments_and_Contingencies_3

Commitments and Contingencies - Schedule of Future Minimum Rental Payments (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
2015	$1,450
2016	1,489
2017	1,529
2018	1,911
2019	1,995
Thereafter	2,224
Future minimum rent	$10,598

Equity_Additional_Information_

Equity - Additional Information (Detail) (USD $)	0 Months Ended	12 Months Ended			0 Months Ended
In Millions, except Per Share data, unless otherwise specified	24-May-13	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Feb. 17, 2015	Feb. 10, 2015	Jan. 27, 2015
Class of Stock [Line Items]
Common shares issued	7.5
Price per share of common shares	$14.70
Generated net proceeds after deducting the underwriting discount and offering costs	$105.10
Net proceeds to repay secured bridge loan	10
Proceeds from issuance of common shares used to pay unsecured revolving credit facility	53
Common share dividend per share declared		$0.60	$0.60	$0.80
Subsequent Event [Member]
Class of Stock [Line Items]
Common share dividend per share annualized							$0.60
Dividend paid date					17-Feb-15
Dividend record date						10-Feb-15
Bridge Loan [Member]
Class of Stock [Line Items]
Net proceeds to repay secured bridge loan	$37.50
Series A Preferred Shares [Member]
Class of Stock [Line Items]
Dividends paid on Series A Preferred Shares		$1.94	$1,938	$1.94
Series A Preferred Shares [Member] \| Subsequent Event [Member]
Class of Stock [Line Items]
Common share dividend per share declared							$0.15
Dividends declared on Series A Preferred Shares							$0.48
Dividend declared date							27-Jan-15

Equity_Characterization_of_Com

Equity - Characterization of Company's Dividends (Detail)	12 Months Ended
Equity - Characterization of Company's Dividends (Detail)	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Equity [Abstract]
Common Shares, Ordinary income	72.42%	[1]	13.53%	[1]	0.00%	[1]
Common Shares, Return of capital	27.58%		86.47%		100.00%
Common Shares, Capital gains	0.00%		0.00%		0.00%
Preferred Shares, Ordinary income	100.00%	[1]	100.00%	[1]	19.83%	[1],[2]
Preferred Shares, Return of capital	0.00%		0.00%		27.27%	[2]
Preferred Shares, Capital gains	0.00%		0.00%		52.90%	[2]

[1]	The dividends classified above as ordinary income do not represent bqualified dividend incomeb and, therefore, are not eligible for reduced rates.
[2]	Figures are estimates.

Noncontrolling_Interests_Addit

Noncontrolling Interests - Additional Information (Detail) (USD $)

0 Months Ended

3 Months Ended

12 Months Ended

0 Months Ended

Oct. 16, 2014

Mar. 31, 2014

Dec. 31, 2014

Dec. 31, 2013

Nov. 08, 2013

Sep. 26, 2012

Aug. 04, 2013

Dec. 31, 2012

Oct. 17, 2012

Nov. 30, 2010

Aug. 04, 2011

Sep. 30, 2014

sqft

Buildings

acre

Buildings

Business Acquisition [Line Items]

Lease Expiration Date

31-Jan-21

Area Of Land Available For Development In Additional Building Space

1,400,000

Cost to acquire all of the outstanding common Operating Partnership units not owned by the Company

$32,500,000

Fair value adjustment, cost basis

4,700,000

3,300,000

Percentage of outstanding Operating Partnership units

95.70%

95.20%

Operating Partnership units redeemed

322,302

Outstanding Operating Partnership units not owned by the Company

2,630,577

Operating Partnership units not owned by Company

4.30%

Number Of Common Operating Partnership Units Issued For Additional Space Purchased

3,125

6,718

Operating Partnership units redeemed to common shares

322,302

Common operating partnership units redeemed for cash

Mortgage Loans on Real Estate

37,300,000

Debt Instrument, Basis Spread on Variable Rate

2.50%

Number of buildings

131

146

178

Buildings and improvements

949,683,000

807,198,000

Storey Park [Member]

Business Acquisition [Line Items]

Mortgage Loans on Real Estate

22,000,000

840 First Street, NE [Member]

Business Acquisition [Line Items]

Operating Partnership units fair valued

40,000

400,000

Redland Corporate Center Buildings II & III [Member]

Business Acquisition [Line Items]

Number of buildings

Perseus controlling interest

97.00%

Mortgage loan

68,400,000

Acquired interest

4,600,000

Washington D C Reporting Segment [Member]

Business Acquisition [Line Items]

Lease Expiration Date

31-Aug-13

Development Of Area For Operations By Joint Venture

1.6

Area Of Land Available For Development In Additional Building Space

700,000

Real Estate Investment Investment In Development Project

55,400,000

Buildings and improvements

43,300,000

Washington D C Reporting Segment [Member] | Greyhound Property [Member]

Business Acquisition [Line Items]

Percentage Of Interest In Joint Venture Owned By Entity

97.00%

Greyhound Property [Member]

Business Acquisition [Line Items]

Percentage Of Interest In Joint Venture Owned By Entity

97.00%

Mortgage Loans on Real Estate

22,000,000

Debt Instrument, Basis Spread on Variable Rate

2.50%

Contractual interest rate

5.00%

Maximum [Member] | Washington D C Reporting Segment [Member] | Greyhound Property [Member]

Business Acquisition [Line Items]

Area Of Land Available For Development In Additional Building Space

712,000

Noncontrolling_Interests_Summa

Noncontrolling Interests - Summary of Redeemable Noncontrolling Interests in Operating Partnership (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Noncontrolling Interest [Line Items]
Net loss	($2,869)	($2,920)	$14,582	($4,348)	($6,553)	($4,606)	$10,910	($1,078)	$4,130	($1,714)	($19,979)
Distributions to owners									-35,198	-32,917	-40,730
Redeemable Noncontrolling Interests [Member]
Noncontrolling Interest [Line Items]
Beginning balance				33,221				34,367	33,221	34,367
Net loss									199	-74
Changes in ownership, net									1,465	143
Distributions to owners									-1,578	-1,557
Other comprehensive income									25	342
Ending balance	$33,332				$33,221				$33,332	$33,221

Benefit_Plans_Additional_Infor

Benefit Plans - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended
Benefit Plans - Additional Information (Detail) (USD $)	Feb. 28, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2013	31-May-13
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares for issuance					4,500,000
Reduction in awards available for issuance on the issue of every stock options granted			1
Reduction in awards available for issuance			3.44
Equity awards authorized under 2009 Plan		7,400,000
Common equity awards remained available for issuance by the Company		2,800,000
Stock options awarded		2,200,000
Stock options outstanding		1,100,000
Percentage of options to be vested on the first anniversary of the grant date		25.00%
Percentage of options to be vested after the date of grant in each subsequent quarter		6.25%
Term of stock granted		10 years
Compensation expense associated with trustee share based awards		$500,000	$600,000
Unrecognized compensation cost related to non-vested shares		1,400,000
Weighted-average period for recognition of non-vested shares		2 years 2 months 18 days
Weighted average grant date fair value of the stock options issued		$2.67	$3.61	$3.27
Amount received from the exercise of stock options		174,000	163,000	71,000
Total intrinsic value of options exercised		43,000	43,000	25,000
Non-vested share awards issued	91,466
Future vesting period of second award		19-Feb-15
Number of common shares issued to independent non-employee trustees		58,815,000	58,704,000
Total fair value of vested shares		2,000,000	3,800,000	4,200,000
Eligibility for contribution by employees			After 60 days of consecutive service
Company matching employee contribution percentage		6.00%	6.00%
Year of consecutive service		0 years 0 months 60 days
Vesting of employer contributions occurrence percentage		4 years
Company's contribution		600,000	600,000	500,000
Stock issued during period, shares		200,000
Maximum offering periods		5 years
Offering period of Plan		Not exceed five years
Percentage of fair value of common shares on the offering date for the calculation of purchase price		85.00%
Percentage of fair value of common shares on the purchase date for the calculation of purchase price		85.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Zero coupon risk-free rate time frame		3 months
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Zero coupon risk-free rate time frame		3 years
Non-Officer Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options awarded						135,250
Stock option awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average period for recognition of non-vested shares		4 years 2 months 18 days
Restricted Share Based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to non-vested shares		3,900,000
Non-vested share awards issued	103,075
Number of awards		2
Employee Share Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares issued under the plan		8,950	11,007	14,470
Compensation expense associated with restricted share based awards		20,000	26,000	42,000
Performance Shares [Member] \| Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested share awards issued	11,609
Performance Shares [Member] \| Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested share awards issued		31,808
Performance Shares [Member] \| Chief Operating Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested share awards issued		15,128
Performance Shares [Member] \| General Counsel [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested share awards issued		16,680
Non-Vested Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense associated with trustee share based awards		2,800,000	3,500,000	2,600,000
Non-vested share awards issued		164,675	313,086	355,612
Number of awards	2
Weighted average grant date fair value of shares issued		$12.84	$12.14	$13.87
Non-Vested Share Awards [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate		0.11%
Expected volatility		24.31%
Non-Vested Share Awards [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate		0.40%
Expected volatility		29.11%
Independent Trustees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common shares issued to independent non-employee trustees							29,792
Trustee Restricted Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense associated with trustee share based awards		400,000	400,000	300,000
Employee Severance [Member] \| Non-Vested Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense associated with restricted share based awards		$1,200,000	$700,000

Benefit_Plans_Compensation_Pla

Benefit Plans - Compensation Plans Option Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Option, Beginning Balance	1,089,292	1,384,006	887,168
Option, Granted	135,250	124,250	627,500
Option, Exercised	-17,171	-14,733	-7,326
Option, Expired	-57,500	-298,469
Option, Forfeited	-98,512	-105,762	-123,336
Option, Ending Balance	1,051,359	1,089,292	1,384,006	887,168
Option, Exercisable	552,620	521,723	693,854
Options expected to vest, subsequent to December 31, 2013	485,733
Weighted Average Exercise Price, Beginning Balance	$15.83	$15.91	$16.76
Weighted Average Exercise Price, Granted	$11.61	$12.73	$14.70
Weighted Average Exercise Price, Exercised	$10.10	$11.05	$9.63
Weighted Average Exercise Price, Expired	$19.08	$15
Weighted Average Exercise Price, Forfeited	$14.49	$16.17	$16.25
Weighted Average Exercise Price, Ending Balance	$15.33	$15.83	$15.91	$16.76
Weighted Average Exercise Price, Exercisable	$16.49	$17.25	$17.01
Weighted Average Exercise Price, Options expected to vest, subsequent to December 31, 2013	$14.11
Weighted Average Remaining Contractual Term	6 years 4 months 6 days	6 years 7 months 6 days	5 years 10 months 24 days	4 years 4 months 24 days
Weighted Average Remaining Contractual Term, Exercisable	5 years 1 month 24 days	4 years 10 months 24 days
Weighted Average Remaining Contractual Term, Exercisable	7 years 5 months 30 days		2 years 10 months 31 days
Aggregate Intrinsic Value, Beginning Balance	$109,151	$174,763	$293,930
Aggregate Intrinsic Value, Ending Balance	181,352	109,151	174,763	293,930
Aggregate Intrinsic Value, Exercisable	102,039	109,151	162,593
Aggregate Intrinsic Value, Options expected to vest, subsequent to December 31, 2012	$71,358

Benefit_Plans_Stock_Option_Inf

Benefit Plans - Stock Option Information (Detail) (USD $)	12 Months Ended
Benefit Plans - Stock Option Information (Detail) (USD $)	Dec. 31, 2014
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Option Outstanding - Options	1,051,359
Options Outstanding - Weighted Average Remaining Contractual Life	6 years 3 months 6 days
Options Outstanding - Weighted Average Exercise Price	$15.33
Options Exercisable - Options	552,620
Options Exercisable - Weighted Average Exercise Price	$16.49
2005 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$22.42
Exercise Price Upper Range	$22.54
Option Outstanding - Options	59,000
Options Outstanding - Weighted Average Remaining Contractual Life	0 months 1 day
Options Outstanding - Weighted Average Exercise Price	$22.44
Options Exercisable - Options	59,000
Options Exercisable - Weighted Average Exercise Price	$22.44
2006 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Upper Range	$26.60
Option Outstanding - Options	17,350
Options Outstanding - Weighted Average Remaining Contractual Life	1 year
Options Outstanding - Weighted Average Exercise Price	$26.60
Options Exercisable - Options	17,350
Options Exercisable - Weighted Average Exercise Price	$26.60
2007 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$29.11
Exercise Price Upper Range	$29.24
Option Outstanding - Options	31,500
Options Outstanding - Weighted Average Remaining Contractual Life	2 years
Options Outstanding - Weighted Average Exercise Price	$29.13
Options Exercisable - Options	31,500
Options Exercisable - Weighted Average Exercise Price	$29.13
2008 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Upper Range	$17.29
Option Outstanding - Options	39,000
Options Outstanding - Weighted Average Remaining Contractual Life	3 years
Options Outstanding - Weighted Average Exercise Price	$17.29
Options Exercisable - Options	39,000
Options Exercisable - Weighted Average Exercise Price	$17.29
2009 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Upper Range	$9.30
Option Outstanding - Options	33,346
Options Outstanding - Weighted Average Remaining Contractual Life	4 years
Options Outstanding - Weighted Average Exercise Price	$9.30
Options Exercisable - Options	33,346
Options Exercisable - Weighted Average Exercise Price	$9.30
2010 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Upper Range	$12.57
Option Outstanding - Options	42,705
Options Outstanding - Weighted Average Remaining Contractual Life	5 years
Options Outstanding - Weighted Average Exercise Price	$12.57
Options Exercisable - Options	42,705
Options Exercisable - Weighted Average Exercise Price	$12.57
2011 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$15.17
Exercise Price Upper Range	$17.12
Option Outstanding - Options	77,188
Options Outstanding - Weighted Average Remaining Contractual Life	6 years 1 month 6 days
Options Outstanding - Weighted Average Exercise Price	$16.36
Options Exercisable - Options	72,664
Options Exercisable - Weighted Average Exercise Price	$16.37
2012 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Lower Range	$13.54
Exercise Price Upper Range	$15
Option Outstanding - Options	566,533
Options Outstanding - Weighted Average Remaining Contractual Life	7 years 0 months 6 days
Options Outstanding - Weighted Average Exercise Price	$14.83
Options Exercisable - Options	219,678
Options Exercisable - Weighted Average Exercise Price	$14.68
2013 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Upper Range	$12.73
Option Outstanding - Options	78,987
Options Outstanding - Weighted Average Remaining Contractual Life	8 years
Options Outstanding - Weighted Average Exercise Price	$12.73
Options Exercisable - Options	37,377
Options Exercisable - Weighted Average Exercise Price	$12.73
2015 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Upper Range	$11.61
Option Outstanding - Options	105,750
Options Outstanding - Weighted Average Remaining Contractual Life	9 years
Options Outstanding - Weighted Average Exercise Price	$11.61
Options Exercisable - Options	0
Options Exercisable - Weighted Average Exercise Price	$0

Benefit_Plans_Assumptions_Used

Benefit Plans - Assumptions Used in Fair Value Determination of Stock Option Granted (Detail) (Stock option awards)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock option awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.72%	0.76%	1.28%
Expected volatility	39.00%	49.70%	45.60%
Expected dividend yield	4.66%	4.92%	5.71%
Weighted average expected life of options	5 years	5 years	6 years 7 months 6 days

Benefit_Plans_Summary_of_Compa

Benefit Plans - Summary of Company's Non-vested Share Awards (Detail) (USD $)	1 Months Ended	12 Months Ended
	Feb. 28, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested Shares, Granted	91,466
Non-Vested Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested Shares, Beginning Balance		637,662	673,828	748,968
Non-vested Shares, Granted		164,675	313,086	355,612
Non-vested Shares, Vested		-137,924	-297,778	-309,605
Non-vested Shares, Expired		-29,514	-45,049	-61,944
Non-vested Shares, Expired		-11,478	-6,425	-59,203
Non-vested Shares, Ending Balance		623,421	637,662	673,828
Weighted Average Grant Date Fair Value, Beginning Balance		$13.33	$12.83	$12.67
Weighted Average Grant Date Fair Value, Granted		$12.84	$12.14	$13.87
Weighted Average Grant Date Fair Value, Vested		$14.21	$12.89	$13.52
Weighted Average Grant Date Fair Value, Expired		$10.21	$11.42	$11.36
Weighted Average Grant Date Fair Value, Forfeited		$13.04	$14.01	$15.03
Weighted Average Grant Date Fair Value, Ending Balance		$13.16	$13.33	$12.83

Segment_Information_Additional

Segment Information - Additional Information (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	Integer	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting [Abstract]
Number of distinct operating segments	4
Corporate Assets Not Allocated To Any Reportable Segments	$84,009	$73,209	$75,425
Capital Expenditure For Corporate Assets Not Allocated To Any Reportable Segments	$930	$1,085	$1,444

Segment_Information_Summary_of

Segment Information - Summary of Segment Information (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	sqft				Buildings				sqft	Buildings	Buildings
	Buildings				sqft				Buildings	sqft	sqft
Segment Reporting Information [Line Items]
Number of buildings	131				146				131	146	178
Square Feet	8,790,147				9,100,121				8,790,147	9,100,121	13,451,401
Total revenues	$42,928	$40,055	$39,307	$39,363	$37,517	$37,206	$36,915	$37,179	$161,652	$148,815	$142,962
Property operating expense									-43,252	-38,280	-34,322
Real estate taxes and insurance									-17,360	-16,074	-14,185
Total property operating income									101,040	94,461	94,455
Depreciation and amortization expense									-61,796	-54,567	-51,457
General and administrative									-21,156	-21,979	-23,568
Acquisition costs									-2,681	-602	-49
Other Nonoperating Income (Expense)									4,108
Contingent consideration related to acquisition of property									0	213	-152
Impairment of real estate assets									-3,956	0	-2,444
Other expenses, net										-28,287	-45,251
Benefit from income taxes									0	0	4,142
Income from discontinued operations	505	297	1,538	-857	-1,320	792	16,668	5,601	1,484	21,742	15,943
Net income (loss)									17,043	10,981	-8,381
Total assets	1,618,460				1,502,460				1,618,460	1,502,460	1,717,748
Capital expenditures									50,789	68,002	70,486
Washington, D.C. [Member]
Segment Reporting Information [Line Items]
Number of buildings	6				4				6	4	3
Square Feet	917,008				522,605				917,008	522,605	531,714
Total revenues									33,959	28,208	27,718
Property operating expense									-9,683	-6,693	-5,298
Real estate taxes and insurance									-5,583	-4,792	-3,876
Total property operating income									18,693	16,723	18,544
Total assets	505,842				344,739				505,842	344,739	321,875
Capital expenditures									23,422	26,910	12,023
Maryland [Member]
Segment Reporting Information [Line Items]
Number of buildings	38				53				38	53	62
Square Feet	1,999,332				2,638,988				1,999,332	2,638,988	3,781,379
Total revenues									45,767	41,735	41,726
Property operating expense									-11,482	-10,579	-9,862
Real estate taxes and insurance									-3,907	-3,436	-3,170
Total property operating income									30,378	27,720	28,694
Total assets	360,470				430,498				360,470	430,498	493,267
Capital expenditures									10,185	16,216	23,163
Northern Virginia Reporting Segment [Member]
Segment Reporting Information [Line Items]
Number of buildings	49				51				49	51	56
Square Feet	3,021,509				3,086,057				3,021,509	3,086,057	3,654,527
Total revenues									53,645	51,787	47,207
Property operating expense									-13,352	-12,601	-11,519
Real estate taxes and insurance									-5,592	-5,679	-5,020
Total property operating income									34,701	33,507	30,668
Total assets	439,833				423,839				439,833	423,839	462,667
Capital expenditures									7,816	13,685	20,959
Southern Virginia [Member]
Segment Reporting Information [Line Items]
Number of buildings	38				38				38	38	57
Square Feet	2,852,298				2,852,471				2,852,298	2,852,471	5,483,781
Total revenues									28,281	27,085	26,311
Property operating expense									-8,735	-8,407	-7,643
Real estate taxes and insurance									-2,278	-2,167	-2,119
Total property operating income									17,268	16,511	16,549
Total assets	228,306				230,175				228,306	230,175	364,514
Capital expenditures									$8,436	$10,106	$12,897

Quarterly_Financial_Informatio2

Quarterly Financial Information - Summary of Quarterly Financial Information (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Revenues	$42,928	$40,055	$39,307	$39,363	$37,517	$37,206	$36,915	$37,179	$161,652	$148,815	$142,962
Operating expenses	38,595	36,283	39,579	35,744	33,899	33,663	31,221	32,508	150,201	131,289	126,177
Operating income	4,333	3,772	-272	3,619	3,618	3,543	5,694	4,671	11,451	17,526	16,785
(Loss) income from continuing operations	-402	-248	16,796	-586	-2,421	-2,509	-2,192	-3,638	15,559	-10,761	-24,324
(Loss) income from discontinued operations	505	297	1,538	-857	-1,320	792	16,668	5,601	1,484	21,742	15,943
Less: Net (income) loss attributable to noncontrolling interests	128	131	-652	195	288	211	-466	59	-199	93	986
Net income (loss) attributable to First Potomac Realty Trust	231	180	17,682	-1,248	-3,453	-1,506	14,010	2,022	16,844	11,074	-7,395
Less: Dividends on preferred shares	-3,100	-3,100	-3,100	-3,100	-3,100	-3,100	-3,100	-3,100	-12,400	-12,400	-11,964
Net income (loss) attributable to common shareholders	($2,869)	($2,920)	$14,582	($4,348)	($6,553)	($4,606)	$10,910	($1,078)	$4,130	($1,714)	($19,979)
Basic and diluted earnings per common share:
Income (loss) from continuing operations	($0.06)	($0.05)	$0.22	($0.07)	($0.09)	($0.09)	($0.10)	($0.13)	$0.05	($0.41)	($0.70)
(Loss) income from discontinued operations	$0.01	$0	$0.03	($0.01)	($0.02)	$0.01	$0.30	$0.11	$0.02	$0.38	$0.30
Net (loss) income	($0.05)	($0.05)	$0.25	($0.08)	($0.11)	($0.08)	$0.20	($0.02)	$0.07	($0.03)	($0.40)

Quarterly_Financial_Informatio3

Quarterly Financial Information - Additional Information (Detail)	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Common shares sold	0	7,500,000

Schedule_III_Real_Estate_and_A1

Schedule III - Real Estate and Accumulated Depreciation (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Type	Office
Encumbrances	$305,139
Initial Costs, Land	359,435
Initial Costs, Building and Improvements	856,720
Gross Amount at End of Year, Since Acquisition	288,580
Gross Amount at End of Year, Land	325,214
Gross Amount at End of Year, Building and Improvements	1,179,158
Gross Amount at End of Year, Total	1,504,372
Gross Amount at End of Year, Accumulated Depreciation	215,499
Real Estate, Beginning balance	1,330,180	1,605,722	1,553,802
Real Estate, Acquisitions of rental property	170,823	26,289	0
Real Estate, Capital expenditures	49,860	66,808	69,042
Real Estate, Impairments	-3,956	-4,069	-3,401
Real Estate, Dispositions of rental property	-30,916	-290,777	-10,963
Real Estate, Asset held-for-sale	-643	-55,767	-1,183
Real Estate, Other	-10,976	-18,026	-1,575
Real Estate, Ending balance	1,504,372	1,330,180	1,605,722
Accumulated Depreciation, Beginning balance	185,725	215,154	175,083
Accumulated Depreciation, Depreciation of rental property	-47,625	-48,638	-49,333
Accumulated Depreciation, Assets held-for-sale	-1,631	-13,470	-2,014
Accumulated Depreciation, Dispositions of rental property	-5,712	-54,377	-2,173
Accumulated Depreciation, Other	-10,508	-10,220	-5,075
Accumulated Depreciation, Ending balance	215,499	185,725	215,154
Rumsey Center [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Columbia
Date Acquired	31-Oct-02
Property Type	BP
Encumbrances	8,160
Initial Costs, Land	2,675
Initial Costs, Building and Improvements	10,196
Gross Amount at End of Year, Since Acquisition	3,705
Gross Amount at End of Year, Land	2,675
Gross Amount at End of Year, Building and Improvements	13,901
Gross Amount at End of Year, Total	16,576
Gross Amount at End of Year, Accumulated Depreciation	5,502
Snowden Center [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Columbia
Date Acquired	31-Oct-02
Property Type	BP
Encumbrances	11,081
Initial Costs, Land	3,404
Initial Costs, Building and Improvements	12,824
Gross Amount at End of Year, Since Acquisition	4,238
Gross Amount at End of Year, Land	3,404
Gross Amount at End of Year, Building and Improvements	17,062
Gross Amount at End of Year, Total	20,466
Gross Amount at End of Year, Accumulated Depreciation	6,165
Metro Park North [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Rockville
Date Acquired	31-Dec-04
Property Type	Office
Initial Costs, Land	9,220
Initial Costs, Building and Improvements	32,056
Gross Amount at End of Year, Since Acquisition	2,997
Gross Amount at End of Year, Land	9,220
Gross Amount at End of Year, Building and Improvements	35,053
Gross Amount at End of Year, Total	44,273
Gross Amount at End of Year, Accumulated Depreciation	8,671
Gateway 270 West [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Clarksburg
Date Acquired	31-Jul-06
Property Type	BP
Initial Costs, Land	18,302
Initial Costs, Building and Improvements	20,562
Gross Amount at End of Year, Since Acquisition	5,708
Gross Amount at End of Year, Land	18,302
Gross Amount at End of Year, Building and Improvements	26,270
Gross Amount at End of Year, Total	44,572
Gross Amount at End of Year, Accumulated Depreciation	5,850
Indian Creek Court [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Beltsville
Date Acquired	31-Aug-06
Property Type	BP
Initial Costs, Land	5,673
Initial Costs, Building and Improvements	17,168
Gross Amount at End of Year, Since Acquisition	12,862
Gross Amount at End of Year, Land	5,673
Gross Amount at End of Year, Building and Improvements	30,030
Gross Amount at End of Year, Total	35,703
Gross Amount at End of Year, Accumulated Depreciation	7,563
Ammendale Commerce Center [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Beltsville
Date Acquired	31-Mar-07
Property Type	BP
Initial Costs, Land	2,398
Initial Costs, Building and Improvements	7,659
Gross Amount at End of Year, Since Acquisition	6,116
Gross Amount at End of Year, Land	2,398
Gross Amount at End of Year, Building and Improvements	13,775
Gross Amount at End of Year, Total	16,173
Gross Amount at End of Year, Accumulated Depreciation	5,805
Annapolis Business Center [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Annapolis
Date Acquired	30-Jun-07
Property Type	Office
Encumbrances	0
Initial Costs, Land	6,101
Initial Costs, Building and Improvements	12,602
Gross Amount at End of Year, Since Acquisition	469
Gross Amount at End of Year, Land	6,101
Gross Amount at End of Year, Building and Improvements	13,071
Gross Amount at End of Year, Total	19,172
Gross Amount at End of Year, Accumulated Depreciation	2,469
Cloverleaf Center [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Germantown
Date Acquired	31-Oct-09
Property Type	Office
Initial Costs, Land	7,097
Initial Costs, Building and Improvements	14,211
Gross Amount at End of Year, Since Acquisition	433
Gross Amount at End of Year, Land	7,097
Gross Amount at End of Year, Building and Improvements	14,644
Gross Amount at End of Year, Total	21,741
Gross Amount at End of Year, Accumulated Depreciation	2,322
Redland Corporate Center Buildings II & III [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Rockville
Date Acquired	30-Nov-10
Property Type	Office
Encumbrances	65,816
Initial Costs, Land	17,272
Initial Costs, Building and Improvements	63,480
Gross Amount at End of Year, Since Acquisition	13,869
Gross Amount at End of Year, Land	17,272
Gross Amount at End of Year, Building and Improvements	77,349
Gross Amount at End of Year, Total	94,621
Gross Amount at End of Year, Accumulated Depreciation	12,014
Ten Three Twenty [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Columbia
Date Acquired	28-Feb-11
Property Type	Office
Initial Costs, Land	2,041
Initial Costs, Building and Improvements	5,327
Gross Amount at End of Year, Since Acquisition	11,894
Gross Amount at End of Year, Land	2,041
Gross Amount at End of Year, Building and Improvements	17,221
Gross Amount at End of Year, Total	19,262
Gross Amount at End of Year, Accumulated Depreciation	2,209
Hillside First And Second [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Columbia
Date Acquired	30-Nov-11
Property Type	Office
Encumbrances	12,949
Initial Costs, Land	3,302
Initial Costs, Building and Improvements	10,926
Gross Amount at End of Year, Since Acquisition	968
Gross Amount at End of Year, Land	3,302
Gross Amount at End of Year, Building and Improvements	11,894
Gross Amount at End of Year, Total	15,196
Gross Amount at End of Year, Accumulated Depreciation	827
Five Hundred Forty Gaither Road Redland First [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Rockville
Date Acquired	31-Oct-13
Property Type	Office
Initial Costs, Land	6,458
Initial Costs, Building and Improvements	19,831
Gross Amount at End of Year, Since Acquisition	94
Gross Amount at End of Year, Land	6,457
Gross Amount at End of Year, Building and Improvements	19,926
Gross Amount at End of Year, Total	26,383
Gross Amount at End of Year, Accumulated Depreciation	1,271
Maryland [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	98,006
Initial Costs, Land	83,943
Initial Costs, Building and Improvements	226,842
Gross Amount at End of Year, Since Acquisition	63,353
Gross Amount at End of Year, Land	83,942
Gross Amount at End of Year, Building and Improvements	290,196
Gross Amount at End of Year, Total	374,138
Gross Amount at End of Year, Accumulated Depreciation	60,668
500 First Street, NW [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Capitol Hill
Date Acquired	30-Jun-10
Property Type	Office
Initial Costs, Land	25,806
Initial Costs, Building and Improvements	33,883
Gross Amount at End of Year, Since Acquisition	410
Gross Amount at End of Year, Land	25,806
Gross Amount at End of Year, Building and Improvements	34,293
Gross Amount at End of Year, Total	60,099
Gross Amount at End of Year, Accumulated Depreciation	4,918
440 First Street, NW [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Capitol Hill
Date Acquired	31-Dec-10
Property Type	Office
Encumbrances	32,216
Initial Costs, Land	0
Initial Costs, Building and Improvements	15,300
Gross Amount at End of Year, Since Acquisition	45,601
Gross Amount at End of Year, Land	9,118
Gross Amount at End of Year, Building and Improvements	51,783
Gross Amount at End of Year, Total	60,901
Gross Amount at End of Year, Accumulated Depreciation	913
1211 Connecticut Ave, NW [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	CBD
Date Acquired	31-Dec-10
Property Type	Office
Encumbrances	29,691
Initial Costs, Land	27,077
Initial Costs, Building and Improvements	17,520
Gross Amount at End of Year, Since Acquisition	9,734
Gross Amount at End of Year, Land	27,077
Gross Amount at End of Year, Building and Improvements	27,254
Gross Amount at End of Year, Total	54,331
Gross Amount at End of Year, Accumulated Depreciation	2,286
840 First Street, NE [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	NoMA
Date Acquired	31-Mar-11
Property Type	Office
Encumbrances	36,539
Initial Costs, Land	16,846
Initial Costs, Building and Improvements	60,905
Gross Amount at End of Year, Since Acquisition	11,020
Gross Amount at End of Year, Land	16,846
Gross Amount at End of Year, Building and Improvements	71,925
Gross Amount at End of Year, Total	88,771
Gross Amount at End of Year, Accumulated Depreciation	7,715
Storey Park [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	NoMA
Date Acquired	31-Aug-11
Property Type	Office
Encumbrances	22,000
Initial Costs, Land	43,672
Initial Costs, Building and Improvements	4,194
Gross Amount at End of Year, Since Acquisition	7,578
Gross Amount at End of Year, Land	0
Gross Amount at End of Year, Building and Improvements	55,444
Gross Amount at End of Year, Total	55,444
Gross Amount at End of Year, Accumulated Depreciation	0
1401 K Street, NW [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	East End
Date Acquired	8-Apr-14
Property Type	Office
Encumbrances	36,861
Initial Costs, Land	29,506
Initial Costs, Building and Improvements	23,269
Gross Amount at End of Year, Since Acquisition	-105
Gross Amount at End of Year, Land	29,506
Gross Amount at End of Year, Building and Improvements	23,165
Gross Amount at End of Year, Total	52,671
Gross Amount at End of Year, Accumulated Depreciation	987
11 DuPont Circle, NW [Domain]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	CBD
Date Acquired	24-Sep-14
Property Type	Office
Encumbrances	0
Initial Costs, Land	15,744
Initial Costs, Building and Improvements	64,832
Gross Amount at End of Year, Since Acquisition	3,381
Gross Amount at End of Year, Land	15,744
Gross Amount at End of Year, Building and Improvements	68,214
Gross Amount at End of Year, Total	83,958
Gross Amount at End of Year, Accumulated Depreciation	588
Washington, D.C. [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	157,307
Initial Costs, Land	158,651
Initial Costs, Building and Improvements	219,903
Gross Amount at End of Year, Since Acquisition	77,619
Gross Amount at End of Year, Land	124,097
Gross Amount at End of Year, Building and Improvements	332,078
Gross Amount at End of Year, Total	456,175
Gross Amount at End of Year, Accumulated Depreciation	17,407
Plaza 500 [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Alexandria
Date Acquired	31-Dec-97
Property Type	I
Encumbrances	30,277
Initial Costs, Land	6,265
Initial Costs, Building and Improvements	35,433
Gross Amount at End of Year, Since Acquisition	6,499
Gross Amount at End of Year, Land	6,268
Gross Amount at End of Year, Building and Improvements	41,929
Gross Amount at End of Year, Total	48,197
Gross Amount at End of Year, Accumulated Depreciation	17,897
Van Buren Office Park [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Herndon
Date Acquired	31-Dec-97
Property Type	Office
Encumbrances	6,790
Initial Costs, Land	3,592
Initial Costs, Building and Improvements	7,652
Gross Amount at End of Year, Since Acquisition	5,446
Gross Amount at End of Year, Land	3,607
Gross Amount at End of Year, Building and Improvements	13,083
Gross Amount at End of Year, Total	16,690
Gross Amount at End of Year, Accumulated Depreciation	5,084
Newington Business Park Center [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Lorton
Date Acquired	31-Dec-99
Property Type	I
Initial Costs, Land	3,135
Initial Costs, Building and Improvements	10,354
Gross Amount at End of Year, Since Acquisition	4,094
Gross Amount at End of Year, Land	3,135
Gross Amount at End of Year, Building and Improvements	14,448
Gross Amount at End of Year, Total	17,583
Gross Amount at End of Year, Accumulated Depreciation	5,798
Herndon Corporate Center [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Herndon
Date Acquired	30-Apr-04
Property Type	Office
Initial Costs, Land	4,082
Initial Costs, Building and Improvements	14,651
Gross Amount at End of Year, Since Acquisition	1,666
Gross Amount at End of Year, Land	4,082
Gross Amount at End of Year, Building and Improvements	16,317
Gross Amount at End of Year, Total	20,399
Gross Amount at End of Year, Accumulated Depreciation	4,670
Windsor at Battlefield [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Manassas
Date Acquired	31-Dec-04
Property Type	Office
Initial Costs, Land	3,228
Initial Costs, Building and Improvements	11,696
Gross Amount at End of Year, Since Acquisition	3,444
Gross Amount at End of Year, Land	3,228
Gross Amount at End of Year, Building and Improvements	15,140
Gross Amount at End of Year, Total	18,368
Gross Amount at End of Year, Accumulated Depreciation	5,384
Reston Business Campus [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Reston
Date Acquired	31-Mar-05
Property Type	Office
Initial Costs, Land	1,996
Initial Costs, Building and Improvements	8,778
Gross Amount at End of Year, Since Acquisition	3,501
Gross Amount at End of Year, Land	1,996
Gross Amount at End of Year, Building and Improvements	12,279
Gross Amount at End of Year, Total	14,275
Gross Amount at End of Year, Accumulated Depreciation	2,961
Enterprise Center [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Chantilly
Date Acquired	30-Apr-05
Property Type	Office
Initial Costs, Land	3,727
Initial Costs, Building and Improvements	27,274
Gross Amount at End of Year, Since Acquisition	4,221
Gross Amount at End of Year, Land	3,728
Gross Amount at End of Year, Building and Improvements	31,494
Gross Amount at End of Year, Total	35,222
Gross Amount at End of Year, Accumulated Depreciation	8,992
Gateway Centre Manassas [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Manassas
Date Acquired	31-Jul-05
Property Type	BP
Encumbrances	432
Initial Costs, Land	3,015
Initial Costs, Building and Improvements	6,734
Gross Amount at End of Year, Since Acquisition	1,524
Gross Amount at End of Year, Land	3,015
Gross Amount at End of Year, Building and Improvements	8,258
Gross Amount at End of Year, Total	11,273
Gross Amount at End of Year, Accumulated Depreciation	2,406
403/405 Glenn Drive [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Sterling
Date Acquired	31-Oct-05
Property Type	BP
Initial Costs, Land	3,940
Initial Costs, Building and Improvements	12,547
Gross Amount at End of Year, Since Acquisition	4,371
Gross Amount at End of Year, Land	3,940
Gross Amount at End of Year, Building and Improvements	16,918
Gross Amount at End of Year, Total	20,858
Gross Amount at End of Year, Accumulated Depreciation	4,716
Linden Business Center [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Manassas
Date Acquired	31-Oct-05
Property Type	BP
Initial Costs, Land	4,829
Initial Costs, Building and Improvements	10,978
Gross Amount at End of Year, Since Acquisition	1,233
Gross Amount at End of Year, Land	4,829
Gross Amount at End of Year, Building and Improvements	12,211
Gross Amount at End of Year, Total	17,040
Gross Amount at End of Year, Accumulated Depreciation	3,258
Prosperity Business Center [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Merrifield
Date Acquired	30-Nov-05
Property Type	BP
Initial Costs, Land	5,881
Initial Costs, Building and Improvements	3,495
Gross Amount at End of Year, Since Acquisition	667
Gross Amount at End of Year, Land	5,881
Gross Amount at End of Year, Building and Improvements	4,162
Gross Amount at End of Year, Total	10,043
Gross Amount at End of Year, Accumulated Depreciation	1,118
Sterling Park Business Center [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Sterling
Date Acquired	28-Feb-06
Property Type	BP
Initial Costs, Land	19,897
Initial Costs, Building and Improvements	10,750
Gross Amount at End of Year, Since Acquisition	20,600
Gross Amount at End of Year, Land	15,614
Gross Amount at End of Year, Building and Improvements	35,633
Gross Amount at End of Year, Total	51,247
Gross Amount at End of Year, Accumulated Depreciation	6,728
Davis Drive [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Sterling
Date Acquired	31-Aug-06
Property Type	BP
Initial Costs, Land	1,614
Initial Costs, Building and Improvements	3,611
Gross Amount at End of Year, Since Acquisition	3,402
Gross Amount at End of Year, Land	1,646
Gross Amount at End of Year, Building and Improvements	6,981
Gross Amount at End of Year, Total	8,627
Gross Amount at End of Year, Accumulated Depreciation	1,610
Three Flint Hill [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Oakton
Date Acquired	30-Apr-10
Property Type	Office
Initial Costs, Land	0
Initial Costs, Building and Improvements	13,653
Gross Amount at End of Year, Since Acquisition	24,459
Gross Amount at End of Year, Land	4,181
Gross Amount at End of Year, Building and Improvements	33,931
Gross Amount at End of Year, Total	38,112
Gross Amount at End of Year, Accumulated Depreciation	5,092
Ashburn Center [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Date Acquired	31-Dec-09
Atlantic Corporate Park [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Sterling
Date Acquired	30-Nov-10
Property Type	Office
Initial Costs, Land	5,895
Initial Costs, Building and Improvements	11,655
Gross Amount at End of Year, Since Acquisition	13,495
Gross Amount at End of Year, Land	5,895
Gross Amount at End of Year, Building and Improvements	25,150
Gross Amount at End of Year, Total	31,045
Gross Amount at End of Year, Accumulated Depreciation	3,451
Cedar Hill [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Tysonbs Corner
Date Acquired	28-Feb-11
Property Type	Office
Initial Costs, Land	5,306
Initial Costs, Building and Improvements	13,554
Gross Amount at End of Year, Since Acquisition	3,173
Gross Amount at End of Year, Land	5,306
Gross Amount at End of Year, Building and Improvements	16,727
Gross Amount at End of Year, Total	22,033
Gross Amount at End of Year, Accumulated Depreciation	2,688
One Fair Oaks [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Fairfax
Date Acquired	30-Apr-11
Property Type	Office
Initial Costs, Land	5,688
Initial Costs, Building and Improvements	43,176
Gross Amount at End of Year, Since Acquisition	6,332
Gross Amount at End of Year, Land	5,688
Gross Amount at End of Year, Building and Improvements	49,508
Gross Amount at End of Year, Total	55,196
Gross Amount at End of Year, Accumulated Depreciation	7,098
1775 Wiehle Avenue [Domain]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Reston
Initial Costs, Land	3,542
Initial Costs, Building and Improvements	30,575
Gross Amount at End of Year, Since Acquisition	0
Gross Amount at End of Year, Land	3,542
Gross Amount at End of Year, Building and Improvements	30,575
Gross Amount at End of Year, Total	34,117
Gross Amount at End of Year, Accumulated Depreciation	687
Northern Virginia [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	37,499
Initial Costs, Land	85,632
Initial Costs, Building and Improvements	276,566
Gross Amount at End of Year, Since Acquisition	108,127
Gross Amount at End of Year, Land	85,581
Gross Amount at End of Year, Building and Improvements	384,744
Gross Amount at End of Year, Total	470,325
Gross Amount at End of Year, Accumulated Depreciation	89,638
Crossways Commerce Center [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Chesapeake
Date Acquired	31-Dec-99
Property Type	BP
Initial Costs, Land	5,160
Initial Costs, Building and Improvements	23,660
Gross Amount at End of Year, Since Acquisition	13,517
Gross Amount at End of Year, Land	5,160
Gross Amount at End of Year, Building and Improvements	37,177
Gross Amount at End of Year, Total	42,337
Gross Amount at End of Year, Accumulated Depreciation	14,030
Greenbrier Technology Center II [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Chesapeake
Date Acquired	31-Oct-02
Property Type	BP
Encumbrances	4,452
Initial Costs, Land	1,365
Initial Costs, Building and Improvements	5,119
Gross Amount at End of Year, Since Acquisition	1,042
Gross Amount at End of Year, Land	1,365
Gross Amount at End of Year, Building and Improvements	6,161
Gross Amount at End of Year, Total	7,526
Gross Amount at End of Year, Accumulated Depreciation	2,195
Norfolk Business Center [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Norfolk
Date Acquired	31-Oct-02
Property Type	BP
Encumbrances	4,183
Initial Costs, Land	1,323
Initial Costs, Building and Improvements	4,967
Gross Amount at End of Year, Since Acquisition	952
Gross Amount at End of Year, Land	1,324
Gross Amount at End of Year, Building and Improvements	5,918
Gross Amount at End of Year, Total	7,242
Gross Amount at End of Year, Accumulated Depreciation	2,186
Crossways II [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Chesapeake
Date Acquired	31-Oct-04
Property Type	BP
Initial Costs, Land	1,036
Initial Costs, Building and Improvements	6,254
Gross Amount at End of Year, Since Acquisition	1,165
Gross Amount at End of Year, Land	1,036
Gross Amount at End of Year, Building and Improvements	7,419
Gross Amount at End of Year, Total	8,455
Gross Amount at End of Year, Accumulated Depreciation	2,182
Norfolk Commerce Park II [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Norfolk
Date Acquired	31-Oct-04
Property Type	BP
Initial Costs, Land	1,221
Initial Costs, Building and Improvements	8,693
Gross Amount at End of Year, Since Acquisition	4,364
Gross Amount at End of Year, Land	1,221
Gross Amount at End of Year, Building and Improvements	13,057
Gross Amount at End of Year, Total	14,278
Gross Amount at End of Year, Accumulated Depreciation	4,123
1434 Crossways Boulevard [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Chesapeake
Date Acquired	31-Aug-05
Property Type	BP
Initial Costs, Land	4,447
Initial Costs, Building and Improvements	24,739
Gross Amount at End of Year, Since Acquisition	3,211
Gross Amount at End of Year, Land	4,815
Gross Amount at End of Year, Building and Improvements	27,582
Gross Amount at End of Year, Total	32,397
Gross Amount at End of Year, Accumulated Depreciation	6,457
Crossways I [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Chesapeake
Date Acquired	28-Feb-06
Property Type	BP
Initial Costs, Land	2,657
Initial Costs, Building and Improvements	11,597
Gross Amount at End of Year, Since Acquisition	2,810
Gross Amount at End of Year, Land	2,646
Gross Amount at End of Year, Building and Improvements	14,418
Gross Amount at End of Year, Total	17,064
Gross Amount at End of Year, Accumulated Depreciation	3,647
Crossways Commerce Center IV [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Chesapeake
Date Acquired	31-May-06
Property Type	BP
Initial Costs, Land	1,292
Initial Costs, Building and Improvements	3,899
Gross Amount at End of Year, Since Acquisition	700
Gross Amount at End of Year, Land	1,292
Gross Amount at End of Year, Building and Improvements	4,599
Gross Amount at End of Year, Total	5,891
Gross Amount at End of Year, Accumulated Depreciation	1,390
Gateway II [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Norfolk
Date Acquired	30-Nov-06
Property Type	BP
Initial Costs, Land	1,320
Initial Costs, Building and Improvements	2,293
Gross Amount at End of Year, Since Acquisition	818
Gross Amount at End of Year, Land	1,320
Gross Amount at End of Year, Building and Improvements	3,111
Gross Amount at End of Year, Total	4,431
Gross Amount at End of Year, Accumulated Depreciation	801
Greenbrier Circle Corporate Center [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Chesapeake
Date Acquired	31-Jan-07
Property Type	BP
Initial Costs, Land	4,164
Initial Costs, Building and Improvements	18,984
Gross Amount at End of Year, Since Acquisition	4,101
Gross Amount at End of Year, Land	4,164
Gross Amount at End of Year, Building and Improvements	23,085
Gross Amount at End of Year, Total	27,249
Gross Amount at End of Year, Accumulated Depreciation	5,375
Greenbrier Technology Center I [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Chesapeake
Date Acquired	31-Jan-07
Property Type	BP
Initial Costs, Land	2,024
Initial Costs, Building and Improvements	7,960
Gross Amount at End of Year, Since Acquisition	1,703
Gross Amount at End of Year, Land	2,024
Gross Amount at End of Year, Building and Improvements	9,663
Gross Amount at End of Year, Total	11,687
Gross Amount at End of Year, Accumulated Depreciation	2,614
Battlefield Corporate Center [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Chesapeake
Date Acquired	31-Oct-10
Property Type	BP
Encumbrances	3,692
Initial Costs, Land	1,860
Initial Costs, Building and Improvements	6,071
Gross Amount at End of Year, Since Acquisition	786
Gross Amount at End of Year, Land	1,881
Gross Amount at End of Year, Building and Improvements	6,836
Gross Amount at End of Year, Total	8,717
Gross Amount at End of Year, Accumulated Depreciation	926
Greenbrier Towers [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Location	Chesapeake
Date Acquired	31-Jul-11
Property Type	Office
Initial Costs, Land	2,997
Initial Costs, Building and Improvements	9,173
Gross Amount at End of Year, Since Acquisition	3,849
Gross Amount at End of Year, Land	2,997
Gross Amount at End of Year, Building and Improvements	13,022
Gross Amount at End of Year, Total	16,019
Gross Amount at End of Year, Accumulated Depreciation	1,775
Southern Virginia [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	12,327
Initial Costs, Land	30,866
Initial Costs, Building and Improvements	133,409
Gross Amount at End of Year, Since Acquisition	39,018
Gross Amount at End of Year, Land	31,245
Gross Amount at End of Year, Building and Improvements	172,048
Gross Amount at End of Year, Total	203,293
Gross Amount at End of Year, Accumulated Depreciation	47,701
Land Held for Future Development [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial Costs, Land	343
Initial Costs, Building and Improvements	0
Gross Amount at End of Year, Since Acquisition	371
Gross Amount at End of Year, Land	349
Gross Amount at End of Year, Building and Improvements	0
Gross Amount at End of Year, Total	349
Gross Amount at End of Year, Accumulated Depreciation	0
Other [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Initial Costs, Land	0
Initial Costs, Building and Improvements	0
Gross Amount at End of Year, Since Acquisition	92
Gross Amount at End of Year, Land	0
Gross Amount at End of Year, Building and Improvements	92
Gross Amount at End of Year, Total	92
Gross Amount at End of Year, Accumulated Depreciation	$85

Schedule_III_Additional_Inform

Schedule III - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Tax basis of real estate assets	1,576	$1,667
Minimum [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Estimated lives of Company's assets	5 years
Maximum [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Estimated lives of Company's assets	39 years