Franklin Street Properties (FSP) 10-K 16 Feb 21 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Feb. 05, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2020
Entity File Number	001-32470
Entity Registrant Name	FRANKLIN STREET PROPERTIES CORP.
Entity Incorporation, State or Country Code	MD
Entity Tax Identification Number	04-3578653
Entity Address, Address Line One	401 Edgewater Place, Suite 200
Entity Address, City or Town	Wakefield
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	01880
City Area Code	781
Local Phone Number	557-1300
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 523,709,269
Title of 12(b) Security	Common Stock
Trading Symbol	FSP
Security Exchange Name	NYSEAMER
Entity Common Stock, Shares Outstanding		107,328,199
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Central Index Key	0001031316
Amendment Flag	false

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Real estate assets:
Land	$ 189,155	$ 191,578
Buildings and improvements	1,938,629	1,924,664
Fixtures and equipment	12,949	11,665
Total real estate assets, gross	2,140,733	2,127,907
Less accumulated depreciation	538,717	490,697
Real estate assets, net	1,602,016	1,637,210
Acquired real estate leases, less accumulated amortization of $55,447 and $60,749, respectively	28,206	40,704
Cash, cash equivalents and restricted cash	4,150	9,790
Tenant rent receivables	7,656	3,851
Straight-line rent receivable	67,789	66,881
Prepaid expenses and other assets	5,752	7,246
Other assets: derivative asset		3,022
Related party mortgage loan receivable	21,000	21,000
Office computers and furniture, net of accumulated depreciation of $1,443 and $1,362, respectively	163	183
Deferred leasing commissions, net of accumulated amortization of $30,411 and $28,114, respectively	56,452	52,767
Total assets	1,793,184	1,842,654
Liabilities:
Bank note payable	3,500
Term loans payable, less unamortized financing costs of $2,677 and $4,267, respectively	717,323	765,733
Series A & Series B Senior Notes, less unamortized financing costs of $822 and $985, respectively	199,178	199,015
Accounts payable and accrued expenses	72,058	66,658
Accrued compensation	3,918	3,400
Tenant security deposits	8,677	9,346
Lease liability	1,536	1,890
Other liabilities: derivative liabilities	17,311	7,704
Acquired unfavorable real estate leases, less accumulated amortization of $4,031 and $4,676, respectively	1,592	2,512
Total liabilities	1,025,093	1,056,258
Commitments and contingencies
Stockholders' Equity:
Preferred stock, $.0001 par value, 20,000,000 shares authorized, none issued or outstanding
Common stock, $.0001 par value, 180,000,000 shares authorized, 107,328,199 and 107,269,201 shares issued and outstanding, respectively	11	11
Additional paid-in capital	1,357,131	1,356,794
Accumulated other comprehensive income (loss)	(17,311)	(4,682)
Distributions in excess of accumulated earnings	(571,740)	(565,727)
Total stockholders' equity	768,091	786,396
Total liabilities and stockholders' equity	$ 1,793,184	$ 1,842,654

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Consolidated Balance Sheets
Acquired real estate leases, accumulated amortization	$ 55,447	$ 60,749
Office computers and furniture, accumulated depreciation	1,443	1,362
Deferred leasing commissions, accumulated amortization	30,411	28,114
Term loan payable, unamortized financing costs	2,677	4,267
Series A & Series B Senior notes, unamortized financing costs	822	985
Acquired unfavorable real estate leases, accumulated amortization	$ 4,031	$ 4,676
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	20,000,000	20,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	180,000,000	180,000,000
Common stock, shares issued (in shares)	107,328,199	107,269,201
Common stock, shares outstanding (in shares)	107,328,199	107,269,201

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues:
Rental			$ 263,777
Rental	$ 244,207	$ 265,527
Total revenues	245,848	269,065	268,870
Expenses:
Real estate operating expenses	66,940	72,311	70,703
Real estate taxes and insurance	48,390	47,871	45,857
Depreciation and amortization	88,558	90,909	94,230
General and administrative	14,997	14,473	13,070
Interest	36,026	36,757	38,374
Total expenses	254,911	262,321	262,234
Gain on sale of property	41,928
Income before taxes on income and equity in income of non-consolidated REITs	32,865	6,744	6,636
Tax expense on income	250	269	360
Equity in income of non-consolidated REITs			6,793
Net income	$ 32,615	$ 6,475	$ 13,069
Weighted average number of shares outstanding, basic and diluted	107,303,000	107,233,000	107,231,000
Net income per share, basic and diluted	$ 0.30	$ 0.06	$ 0.12
Rental
Revenues:
Rental			$ 263,777
Rental	$ 244,207	$ 265,527
Related party revenue: Management fees and interest income from loans
Revenues:
Revenue	1,610	3,517	5,061
Related party revenue: Other
Revenues:
Revenue	$ 31	$ 21	$ 32

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Consolidated Statements of Comprehensive Income (Loss)
Net income	$ 32,615	$ 6,475	$ 13,069
Other comprehensive income (loss):
Unrealized gain (loss) on derivative financial instruments	(12,629)	(19,447)	2,599
Total other comprehensive income (loss)	(12,629)	(19,447)	2,599
Comprehensive income (loss)	$ 19,986	$ (12,972)	$ 15,668

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated other comprehensive income (loss)	Distributions in excess of accumulated earnings	Total
Balance at Dec. 31, 2017	$ 11	$ 1,356,457	$ 12,166	$ (497,342)	$ 871,292
Balance (in shares) at Dec. 31, 2017	107,231
Increase (Decrease) in Stockholders' Equity
Comprehensive income (loss)			2,599	13,069	15,668
Distributions				(49,326)	(49,326)
Balance at Dec. 31, 2018	$ 11	1,356,457	14,765	(533,599)	837,634
Balance (in shares) at Dec. 31, 2018	107,231
Increase (Decrease) in Stockholders' Equity
Comprehensive income (loss)			(19,447)	6,475	(12,972)
Distributions				(38,603)	(38,603)
Equity-based compensation		337			337
Equity-based compensation (in shares)	38
Balance at Dec. 31, 2019	$ 11	1,356,794	(4,682)	(565,727)	786,396
Balance (in shares) at Dec. 31, 2019	107,269
Increase (Decrease) in Stockholders' Equity
Comprehensive income (loss)			(12,629)	32,615	19,986
Distributions				(38,628)	(38,628)
Equity-based compensation		337			337
Equity-based compensation (in shares)	59
Balance at Dec. 31, 2020	$ 11	$ 1,357,131	$ (17,311)	$ (571,740)	$ 768,091
Balance (in shares) at Dec. 31, 2020	107,328

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net income	$ 32,615	$ 6,475	$ 13,069
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense	91,581	93,787	97,171
Amortization of above and below market leases	(313)	(402)	(556)
Shares issued as compensation	337	337
Gain on sale of property	(41,928)
Equity in income of non-consolidated REITs			(6,793)
Decrease in allowance for doubtful accounts and write-off of accounts receivable	(13)	(71)	(50)
Changes in operating assets and liabilities:
Tenant rent receivables	(3,792)	158	(765)
Straight-line rents	(1,685)	(8,876)	381
Lease acquisition costs	(2,123)	(3,999)	(1,193)
Prepaid expenses and other assets	(129)	2,313	(1,940)
Accounts payable and accrued expenses	7,785	3,910	(4,077)
Accrued compensation	518	357	(598)
Tenant security deposits	(669)	3,027	936
Payment of deferred leasing commissions	(13,735)	(15,101)	(15,383)
Net cash provided by operating activities	68,449	81,915	80,202
Cash flows from investing activities:
Property improvements, fixtures and equipment	(77,919)	(70,746)	(51,057)
Investment in non-consolidated REITs			74,931
Distributions in excess of earnings from non-consolidated REITs			710
Investment in related party mortgage loan receivable		(2,400)
Repayment of related party mortgage loan receivable		52,060	1,060
Proceeds received on sales of real estate assets	88,958
Proceeds received from liquidating trust		1,470
Net cash provided by (used in) investing activities	11,039	(19,616)	25,644
Cash flows from financing activities:
Distributions to stockholders	(38,628)	(38,603)	(49,326)
Borrowings under bank note payable	105,000	45,000	38,000
Repayments of bank note payable	(101,500)	(70,000)	(91,000)
Repayment on term loan payable	(50,000)
Deferred financing costs		(83)	(2,162)
Net cash used in financing activities	(85,128)	(63,686)	(104,488)
Net increase (decrease) in cash, cash equivalents and restricted cash	(5,640)	(1,387)	1,358
Cash, cash equivalents and restricted cash, beginning of year	9,790	11,177	9,819
Cash, cash equivalents and restricted cash, end of period	4,150	9,790	11,177
Cash paid for:
Interest	33,060	34,470	35,885
Taxes on income	477	508	485
Non-cash investing and financing activities:
Accrued costs for purchase of real estate assets	$ 8,625	$ 11,012	$ 7,361

Organization

Organization	12 Months Ended
	Dec. 31, 2020
Organization
Organization	1. Organization ​ Franklin Street Properties Corp. (“FSP Corp.” or the “Company”), holds, directly and indirectly, 100% of the interest in FSP Investments LLC, FSP Property Management LLC, FSP Holdings LLC and FSP Protective TRS Corp. FSP Property Management LLC provides asset management and property management services. The Company also has a non-controlling common stock interest in two corporations organized to operate as real estate investment trusts (“REIT”). Collectively, the two REITs are referred to as the “Sponsored REITs”. ​ As of December 31, 2020, the Company owned and operated a portfolio of real estate consisting of 32 operating properties, two redevelopment properties and two managed Sponsored REITs and held one promissory note secured by a mortgage on real estate owned by a Sponsored REIT. From time-to-time, the Company may acquire real estate or make additional secured loans. The Company may also pursue, on a selective basis, the sale of its properties in order to take advantage of the value creation and demand for its properties, or for geographic or property specific reasons.

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Significant Accounting Policies
Significant Accounting Policies	2. Significant Accounting Policies ​ Basis of Presentation ​ The accompanying consolidated financial statements include all of the accounts of the Company and its majority-owned subsidiaries. All significant intercompany accounts and transactions have been eliminated in consolidation. ​ Estimates and Assumptions ​ The Company prepares its financial statements and related notes in conformity with generally accepted accounting principles in the United States of America (“GAAP”). These principles require management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Actual results could differ from those estimates. Significant estimates in the consolidated financial statements include the allowance for doubtful accounts, purchase price allocations, impairment considerations, useful lives of fixed assets and the valuation of derivatives. ​ Investments in non-consolidated REITs ​ As of December 31, 2020, the Company has a non-controlling common stock interest in two Sponsored REITs in which the Company no longer shares in economic benefit or risk. The Company had a non-controlling common stock interest in another Sponsored REIT and a non-controlling preferred stock interest in additional Sponsored REITs, each of which were liquidated during 2019 or 2018. The Company exercised influence over, but did not control these entities and investments were accounted for using the equity method. Under the equity method of accounting, the Company's cost basis was adjusted by its share of the Sponsored REITs' earnings or losses. ​ The equity investments in Sponsored REITS were reviewed for impairment each reporting period. The Company recorded impairment charges when events or circumstances indicated a decline in the fair value below the carrying value of the investment had occurred and such decline was other-than-temporary. ​ On December 27, 2007, the Company purchased 965.75 preferred shares (approximately 43.7%) of a Sponsored REIT, FSP 303 East Wacker Drive Corp. (“East Wacker”), for $82.8 million. The Company agreed to vote its shares in any matter presented to a vote by the stockholders of East Wacker in the same proportion as shares voted by other stockholders of East Wacker. The investment in East Wacker was accounted for under the equity method. On September 24, 2018, the property owned by East Wacker was sold and, thereafter, East Wacker declared and issued a liquidating distribution to its preferred shareholders. ​ On May 29, 2009, the Company purchased 175.5 preferred shares (approximately 27.0%) of a Sponsored REIT, FSP Grand Boulevard Corp. (“Grand Boulevard”), for $15.0 million. The Company agreed to vote its shares in any matter presented to a vote by the stockholders of Grand Boulevard in the same proportion as shares voted by other stockholders of Grand Boulevard. The investment in Grand Boulevard was accounted for under the equity method. On July 19, 2018, the property owned by Grand Boulevard was sold and, thereafter, Grand Boulevard declared and issued a liquidating distribution for its preferred shareholders. ​ Real Estate and Depreciation ​ Real estate assets are stated at cost less accumulated depreciation. ​ The Company allocates the value of real estate acquired among land, buildings and identified intangible assets or liabilities. Costs related to land, building and improvements are capitalized. Typical capital items include new roofs, site improvements, various exterior building improvements and major interior renovations. Costs incurred in connection with leasing (primarily tenant improvements and leasing commissions) are capitalized and amortized over the lease period. Routine replacements and ordinary maintenance and repairs that do not extend the life of the asset are expensed as incurred. Depreciation is computed using the straight-line method over the assets’ estimated useful lives as follows: ​ ​ ​ ​ ​ ​ ​ Category Years Commercial buildings ​ 39 ​ ​ Building improvements 15 - 39 ​ Fixtures and equipment 3 - 7 ​ ​ The Company reviews its properties to determine if their carrying amounts will be recovered from future operating cash flows if certain indicators of impairment are identified at those properties. These indicators may include declining tenant occupancy, weak or declining tenant profitability, cash flows or liquidity, the Company’s decision to dispose of an asset before the end of its estimated useful life or legislative, economic, or market changes that permanently reduce the value of the Company’s investment. If indicators of impairment are present, the Company evaluates the carrying value of the property by comparing it to its expected future undiscounted cash flow. If the Company determines that impairment has occurred, the affected assets are reduced to their fair value. The evaluation of anticipated cash flows is highly subjective and is based in part on assumptions regarding future occupancy, rental rates and capital requirements that could differ materially from actual results in future periods. Since cash flows are considered on an undiscounted basis in the analysis that the Company conducts to determine whether an asset has been impaired, the Company’s strategy of holding properties over the long term directly decreases the likelihood of recording an impairment loss. If the Company’s strategy changes or market conditions otherwise dictate an earlier sale date, an impairment loss may be recognized. The Company did not recognize any impairment losses for the years ended December 31, 2020, 2019 or 2018. ​ Acquired Real Estate Leases and Amortization ​ Acquired real estate leases represent costs associated with acquiring an in-place lease (i.e., the market cost to execute a similar lease, including leasing commission, tenant improvements, legal, vacancy and other related costs) and the value relating to leases with rents above the market rate. Amortization is computed using the straight-line method over the term of the leases, which range from 47 months to 176 months . Amortization of these combined components was approximately $12.5 million, $18.9 million and $26.9 million for the years ended December 31, 2020, 2019 and 2018, respectively. ​ ​ Amortization related to costs associated with acquiring an in-place lease is included in depreciation and amortization on the consolidated statements of income. Amortization related to leases with rents above the market rate is offset against the rental revenue in the consolidated statements of income. The estimated annual amortization expense for the five years and thereafter following December 31, 2020 is as follows: ​ ​ ​ ​ ​ ​ (in thousands) December 31, 2021 ​ $ 8,975 ​ 2022 ​ 5,400 ​ 2023 ​ 4,268 ​ 2024 ​ 3,550 ​ 2025 ​ 2,797 ​ 2026 and thereafter ​ 3,216 ​ ​ Acquired Unfavorable Real Estate Leases and Amortization ​ Acquired unfavorable real estate leases represent the value relating to leases with rents below the market rate. Amortization is computed using the straight-line method over the term of the leases, which range from 50 months to 176 months . Amortization expense was approximately $0.9 million, $1.3 million and $2.0 million for the years ended December 31, 2020, 2019 and 2018, respectively. ​ Amortization related to leases with rents below the market rate is included with rental revenue in the consolidated statements of income. The estimated annual amortization for the five years and thereafter following December 31, 2020 is as follows: ​ ​ ​ ​ ​ ​ (in thousands) December 31, 2021 ​ $ 597 ​ 2022 ​ 323 ​ 2023 ​ 218 ​ 2024 ​ 144 ​ 2025 ​ 92 ​ 2026 and thereafter ​ 218 ​ ​ Asset Held For Sale ​ Classification of a property as held for sale typically occurs upon the execution of a purchase and sale agreement and belief by management that the sale or disposition is probable of occurrence within one year . Upon determining that a property was held for sale, the Company discontinues depreciating the property and reflects the property in its consolidated balance sheet at the lower of its carrying amount or fair value less the cost to sell. The Company presents the property held for sale on its consolidated balance sheet as “Asset held for sale”. The Company reports the results of operations of its properties sold or held for sale in its consolidated statements of income through the date of sale. ​ Cash and Cash Equivalents ​ The Company considers all highly liquid instruments purchased with an original maturity of three months or less to be cash equivalents. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the consolidated balance sheets that sum to the total of the same such amounts shown in the consolidated statement of cash flows. ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, December 31, (in thousands) ​ 2020 ​ 2019 Cash and cash equivalents ​ $ 2,650 ​ $ 9,790 Restricted cash ​ 1,500 ​ — Total cash, cash equivalents and restricted cash ​ $ 4,150 ​ $ 9,790 ​ ​ Restricted Cash ​ Restricted cash consists of tenant security deposits, which are required by law in some states or by contractual agreement to be kept in a segregated account, and escrows arising from property sales. Tenant security deposits are refunded when tenants vacate, provided that the tenant has not damaged the property. ​ Cash held in escrow is paid when the related issue is resolved. Restricted cash also may include funds segregated for specific tenant improvements per lease agreements. ​ Tenant Rent Receivables ​ Tenant rent receivables are expected to be collected within one year . The Company provided an allowance for doubtful accounts based on collectability. Lessors recognize the effect of a change in their assessment of whether the collectability of operating lease receivables are probable as an adjustment to lease income rather than bad debt expense. ​ Related Party Mortgage Loan Receivable ​ Management monitors and evaluates the secured loans compared to the expected performance, cash flow and value of the underlying real estate and has not experienced a loss on these loans to date. ​ Concentration of Credit Risks ​ Financial instruments that potentially subject the Company to concentrations of credit risk consist primarily of cash investments, derivatives, related party mortgage loan receivable and accounts receivable. The Company maintains its cash balances principally in banks which the Company believes to be creditworthy. The Company periodically assesses the financial condition of the banks and believes that the risk of loss is minimal. Cash balances held with various financial institutions frequently exceed the insurance limit of provided by the Federal Deposit Insurance Corporation. The derivatives that the Company has are from interest rate swap agreements that are discussed in Note 5. The related party mortgage loan receivable is held with one Sponsored REIT. The Company performs regular evaluations on the extent and impact of any credit deterioration that could affect the performance and value of the secured property, as well as the financial and operating capability of the borrower. The Company performs ongoing credit evaluations of its tenants and requires certain tenants to provide security deposits or letters of credit. Though these security deposits and letters of credit are insufficient to meet the total value of a tenant’s lease obligation, they are a measure of good faith and a source of funds to offset the economic costs associated with lost rent and the costs associated with re-tenanting the space. The Company has no single tenant which accounts for more than ​ Financial Instruments ​ The Company estimates that the carrying values of cash and cash equivalents, restricted cash, receivables, prepaid expenses, accounts payable and accrued expenses, accrued compensation, and tenant security deposits approximate their fair values based on their short-term maturity and the bank note and term loans payable approximate their fair values as they bear interest at variable interest rates. ​ Straight-line Rent Receivable ​ Certain leases provide for fixed rent increases over the term of the lease. Rental revenue is recognized on a straight-line basis over the related lease term; however, billings by the Company are based on the lease agreements. Straight-line rent receivable, which is the cumulative revenue recognized in excess of amounts billed by the Company, was 31, 2020 and 2019, respectively. Prior to 2020, the Company provided an allowance for doubtful accounts based on collectability. Lessors recognized the effect of a change in their assessment of whether the collectability of operating lease receivables are probable as an adjustment to lease income rather than bad debt expense. The reserve was eliminated during 2020 and no changes occurred during 2019 or 2018 based on such assessment. ​ Deferred Leasing Commissions ​ Deferred leasing commissions represent direct and incremental external leasing costs incurred in the leasing of commercial space. These costs are capitalized and are amortized on a straight-line basis over the terms of the related lease agreements. Amortization expense was approximately ​ The estimated annual amortization for the five years and thereafter following December 31, 2020 is as follows: ​ ​ ​ ​ ​ ​ (in thousands) December 31, 2021 $ 9,957 ​ 2022 9,167 ​ 2023 8,041 ​ 2024 6,797 ​ 2025 5,621 ​ 2026 and thereafter 16,869 ​ ​ Common Share Repurchases ​ The Company recognizes the gross cost of the common shares it repurchases as a reduction in stockholders’ equity using the treasury stock method. Maryland law does not recognize a separate treasury stock account but provides that shares repurchased are classified as authorized but unissued shares. Accordingly, the Company reduces common stock for the par value and the excess of the purchase price over the par value is a reduction to additional paid-in capital. ​ Revenue Recognition ​ Rental Revenue - The Company has retained substantially all of the risks and benefits of ownership of the Company’s commercial properties and accounts for its leases as operating leases. Rental revenue includes income from leases, certain reimbursable expenses, straight-line rent adjustments and other income associated with renting the property. Rental income from leases, which includes rent concessions (including free rent and other lease inducements) and scheduled increases in rental rates during the lease term, is recognized on a straight-line basis. The Company does not have any significant percentage rent arrangements with its commercial property tenants. Reimbursable expenses are included in rental income in the period earned. A summary of rental revenue is shown in the following table: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, (in thousands) 2020 2019 2018 Income from leases ​ $ 180,899 ​ $ 191,828 ​ $ 202,127 ​ Reimbursable expenses ​ 61,310 ​ 64,421 ​ 61,475 ​ Straight-line rent adjustment ​ 1,685 ​ 8,876 ​ (381) ​ Amortization of favorable and unfavorable leases ​ 313 ​ 402 ​ 556 ​ ​ ​ $ 244,207 ​ $ 265,527 ​ $ 263,777 ​ ​ Related Party and Other Revenue - ​ Segment Reporting ​ The Company is a REIT focused on real estate investments primarily in the office market and currently operates in only one segment: real estate operations. ​ Income Taxes ​ Taxes on income for the years ended December 31, 2020, 2019 and 2018 represent taxes incurred by FSP Protective TRS Corp, which is a taxable REIT subsidiary, and the State of Texas franchise tax applicable to FSP Corp., which is classified as an income tax for reporting purposes. ​ Net Income Per Share ​ Basic net income per share is computed by dividing net income by the weighted average number of shares outstanding during the period. Diluted net income per share reflects the potential dilution that could occur if securities or other contracts to issue shares were exercised or converted into shares. There were ​ Derivative Instruments ​ The Company recognizes derivatives on the consolidated balance sheets at fair value. Derivatives that do not qualify, or are not designated as hedge relationships, must be adjusted to fair value through income. Derivative instruments designated in a hedge relationship to mitigate exposure to variability in expected future cash flows, or other types of forecasted transactions, are considered cash flow hedges. Cash flow hedges are accounted for by recording the fair value of the derivative instrument on the consolidated balance sheets as either an asset or liability. To the extent hedges are effective, a corresponding amount, adjusted for swap payments, is recorded in accumulated other comprehensive income within stockholders’ equity. Amounts are then reclassified from accumulated other comprehensive income to the income statement in the period or periods the hedged forecasted transaction affects earnings. Ineffectiveness, if any, is recognized in other comprehensive income (“OCI”) and reclassified into the income statement. The Company reviews the effectiveness of each hedging transaction, which involves estimating future cash flows, at least quarterly. Derivative instruments designated in a hedge relationship to mitigate exposure to changes in the fair value of an asset, liability, or firm commitment attributable to a particular risk, such as interest rate risk, are considered fair value hedges. The Company currently has ​ Fair Value Measurements ​ Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. There is also an established fair value hierarchy which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The standard describes three levels of inputs that may be used to measure fair value. Financial assets and liabilities recorded on the consolidated balance sheets at fair value are categorized based on the inputs to the valuation techniques as follows: ​ Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access. Level 2 inputs are inputs other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. Level 2 inputs may include quoted prices for similar assets and liabilities in active markets, as well as inputs that are observable for the asset or liability (other than quoted prices), such as interest rates and yield curves that are observable at commonly quoted intervals. Level 3 inputs are unobservable inputs for the asset or liability, which is typically based on an entity’s own assumptions, as there is little, if any, related market activity or information. In instances where the determination of the fair value measurement is based on inputs from different levels of the fair value hierarchy, the level in the fair value hierarchy within which the entire fair value measurement falls is based on the lowest level input that is significant to the fair value measurement in its entirety. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment, and considers factors specific to the asset or liability including credit risk, which was not significant to the overall value. These inputs (See Notes 3 and 5) were considered and applied to the Company’s derivative instruments and Sponsored REIT Loan. Level 2 inputs were used to value the interest rate swaps and Level 3 inputs were used to value the Sponsored REIT Loan. ​ Subsequent Events ​ In preparing these consolidated financial statements the Company evaluated events that occurred through the date of issuance of these financial statements for potential recognition or disclosure. ​ Recent Accounting Standards ​ In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13” or “CECL”), which requires that entities use a new forward looking “expected loss” model that generally will result in the earlier recognition of allowance for credit losses. The measurement of expected credit losses is based upon historical experience, current conditions, and reasonable and supportable forecasts that affect the collectability of the reported amount. ASU 2016-13 is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. The Company’s Sponsored REIT Loan (as defined in Note 3 below) receivables are within the scope of this standard and the Company’s analysis was completed using a Probability of Default / Loss Given Default Model. The Company’s receivables associated with its real estate operating leases are not within the scope of this standard. The Company adopted this standard on January 1, 2020. The adoption of this standard did not have a material impact on the Company’s consolidated financial statements. ​ In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”). The ASU is intended to improve the effectiveness of fair value measurement disclosures. ASU 2018-13 is effective for all entities for annual periods beginning after December 15, 2019, and interim periods within those fiscal years. This ASU amends existing fair value measurement disclosure requirements by adding, changing, or removing certain disclosures. The Company adopted this standard on January 1, 2020. The adoption of this standard did not have a material impact on the Company’s consolidated financial statements. ​ In April 2019, the FASB issued ASU No. 2019-04, Codification Improvements to Topics 326, Financial Instruments - Credit Losses, Topic 815 Derivatives and Hedging and Topic 825, Financial Instruments (“ASU 2019-04”). The ASU clarifies areas of guidance related to the recently issued standards on credit losses (Topic 326), derivatives and hedging (Topic 815), and recognition and measurement of financial instruments (Topic 825). ASU 2019-04 is effective for fiscal years beginning after December 15, 2019. The Company adopted this standard on January 1, 2020. The adoption of this standard did not have a material impact on the Company’s consolidated financial statements. ​ In March 2020, the FASB issued ASU No. 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting (“ASU 2020-04”). The ASU contains practical expedients for reference rate reform related activities that impact debt, leases, derivatives and other contracts. The guidance in ASU 2020-04 is optional and may be elected over time as reference rate reform activities occur. The Company is currently assessing the potential impact that the adoption of ASU 2020-04 may have on its consolidated financial statements.

Related Party Transactions and

Related Party Transactions and Investments in Non-Consolidated Entities	12 Months Ended
	Dec. 31, 2020
Related Party Transactions and Investments in Non-Consolidated Entities
Related Party Transactions and Investments in Non-Consolidated Entities	3. Related Party Transactions and Investments in Non-Consolidated Entities ​ Investment in Sponsored REITs ​ The Company held a common stock interest in 2, 2, and 3 Sponsored REITs at December 31, 2020, 2019 and 2018, respectively. The Company held a non-controlling preferred stock investment in two Sponsored REITs, FSP 303 East Wacker Drive Corp. (“East Wacker”) and FSP Grand Boulevard Corp. (“Grand Boulevard”), each of which were liquidated during the three months ended September 30, 2018. ​ In December 2007, the Company purchased 965.75 preferred shares or 43.7% of the outstanding preferred shares of East Wacker. On September 24, 2018, the property owned by East Wacker was sold and, thereafter, East Wacker declared and issued a liquidating distribution for its preferred shareholders, from which the Company was entitled to million. On September 27, 2018, the Company received million distribution. As a result of the sale, the Company recognized a gain on liquidation of million. ​ In May 2009, the Company purchased 175.5 preferred shares or 27.0% of the outstanding preferred shares of Grand Boulevard. On July 19, 2018, the property owned by Grand Boulevard was sold and, thereafter, Grand Boulevard declared and issued a liquidating distribution for its preferred shareholders, from which the Company was entitled to million. On August 17, 2018, the Company received million distribution. As a result of the sale, the Company recognized a loss on liquidation of million. As of December 31, 2020 and 2019, the Company held a beneficial interest in the Grand Boulevard liquidating trust in the amount of ​ Equity in income (loss) of investments in non-consolidated REITs were derived from the Company’s share of income or loss in the operations of those entities and includes gain or loss on liquidation. The Company exercised influence over, but did not control these entities, and investments were accounted for using the equity method. ​ During the year ended December 31, 2019, a property owned by a Sponsored REIT, FSP Energy Tower I Corp. (“Energy Tower”), was sold and, thereafter, liquidating distributions for its preferred shareholders were declared and issued. The Company held a mortgage loan and secured revolving line of credit with this entity, which were secured by the property owned by Energy Tower. The loans with Energy Tower in the aggregate principal amount of million were repaid by the proceeds of the sale. ​ During the year ended December 31, 2018, a property owned by a Sponsored REIT, FSP Centre Pointe V Corp., was sold and, thereafter, liquidating distributions for its preferred shareholders were declared and issued. ​ Equity in income (loss) of investment in non-consolidated REITs: ​ The following table includes equity in income (loss) of investments in non-consolidated REITs: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ ​ ​ December 31, ​ (in thousands) 2018 ​ ​ ​ ​ Equity in income of East Wacker ​ $ 7,209 ​ Equity in loss of Grand Boulevard ​ ​ (107) ​ Impairment charge ​ (309) ​ Total ​ $ 6,793 ​ ​ Equity in income of East Wacker was derived from the Company’s preferred stock investment in the entity. In December 2007, the Company purchased of the outstanding preferred shares, of East Wacker. On September 24, 2018, the property owned by East Wacker was sold at a gain, which is included in equity in income (loss) of non-consolidated REITs on the consolidated statements of income. ​ Equity in loss of Grand Boulevard is derived from the Company’s preferred stock investment in the entity. In May 2009, the Company purchased of the outstanding preferred shares of Grand Boulevard. On July 19, 2018, the property owned by Grand Boulevard was sold at a loss, which is included in equity in income (loss) of non-consolidated REITs on the consolidated statements of income. ​ At June 30, 2018, the Company recognized an impairment charge of $0.3 million, which represented the other-than-temporary decline in the fair value below the carrying value of one of the Company’s investments in non-consolidated REITs. The Company estimated the fair value of its equity investment by estimating the fair value of the property, less estimated costs to sell using a purchase and sale agreement to purchase the property made by third parties (Level 3 inputs, as there is no active market). ​ The following table includes distributions received from non-consolidated REITs: ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ ​ ​ December 31, ​ (in thousands) 2018 ​ ​ ​ ​ ​ Distributions from East Wacker ​ $ 657 ​ Distributions from Grand Boulevard ​ 53 ​ ​ ​ $ 710 ​ ​ Non-consolidated REITs ​ As of December 31, 2020, the Company has a non-controlling common stock interest in two Sponsored REITs in which the Company no longer shares in economic benefit or risk. The balance sheet data below for 2018 includes the Sponsored REITs the Company held an interest in as of December 31, 2018. The operating data below for 2018 includes the operations of the Sponsored REITs the Company held an interest in during the year ended December 31, 2018. ​ Summarized financial information for the Sponsored REITs is as follows: ​ ​ ​ ​ ​ ​ ​ December 31, (in thousands) ​ 2018 ​ ​ ​ ​ Balance Sheet Data (unaudited): ​ ​ ​ ​ Real estate, net ​ $ 97,034 ​ Other assets ​ 18,532 ​ Total liabilities ​ (75,382) ​ Shareholders’ equity ​ $ 40,184 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ ​ ​ December 31, ​ (in thousands) 2018 ​ ​ ​ ​ Operating Data (unaudited): ​ ​ ​ ​ Rental revenues ​ $ 40,382 ​ Other revenues ​ 1 ​ Operating and maintenance expenses ​ (20,584) ​ Depreciation and amortization ​ (13,077) ​ Interest expense ​ (6,869) ​ Gain on sale ​ 17,095 ​ Net income ​ $ 16,948 ​ ​ Management fees and interest income from loans: ​ Asset management fees range from 1% to 5% of collected rents, and the applicable contracts are cancelable with 30 day notice. Asset management fee income from non-consolidated entities amounted to approximately $0.1 million, $0.2 million and $0.5 million for the years ended December 31, 2020, 2019 and 2018, respectively. ​ From time to time the Company may make secured loans (“Sponsored REIT Loans”) to Sponsored REITs in the form of mortgage loans or revolving lines of credit to fund construction costs, capital expenditures, leasing costs and for other purposes. The Company reviews the need for an allowance under CECL for Sponsored REIT loans each reporting period. The Company regularly evaluates the extent and impact of any credit deterioration that could affect performance and the value of the secured property, as well as the financial and operating capability of the borrower. A property’s operating results and existing cash balances are considered and used to assess whether cash flows from operations are sufficient to cover the current and future operating and debt service requirements. The Company also evaluates the borrower’s competency in managing and operating the secured property and considers the overall economic environment, real estate sector and geographic sub-market in which the secured property is located. The Company applies normal loan review and underwriting procedures (as may be implemented or modified from time to time) in making that judgment. ​ The Company anticipates that each Sponsored REIT Loan will be repaid at maturity or earlier from refinancing, long term financings of the underlying properties, cash flows from the underlying properties or some other capital event. Each Sponsored REIT Loan is secured by a mortgage on the underlying property and has a term of approximately one to three years . ​ The following is a summary of the Sponsored REIT Loan outstanding as of December 31, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Maximum Amount Interest (dollars in thousands, except footnotes) ​ ​ Maturity ​ Amount ​ Outstanding Rate at Sponsored REIT Location ​ Date ​ of Loan ​ 31-Dec-20 31-Dec-20 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Mortgage loan secured by property ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ FSP Monument Circle LLC (1) ​ Indianapolis, IN ​ 6-Dec-22 ​ $ 21,000 ​ $ 21,000 7.51 % ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 21,000 ​ $ 21,000 ​ ​ (1) This mortgage loan includes an origination fee of $164,000 and an exit fee of $38,000 when repaid by the borrower. ​ The Company recognized interest income and fees from the Sponsored REIT Loans of approximately $1.5 million, $3.3 million and $4.6 million for the years ended December 31, 2020, 2019 and 2018, respectively. The financial instrument was classified within Level 3 of the fair value hierarchy and had a fair value of approximately million as of December 31, 2020. ​ On December 6, 2020, the Company entered into a second amendment to the Sponsored REIT Loan which qualified as a troubled debt restructuring. The amendment extended the maturity date of the loan for two years and increased the interest rate from 7.19% to 7.51% . There were no commitments to lend additional funds to the Sponsored REIT and the loan is fully collateralized by the mortgage held on the Sponsored REIT's property.

Bank Note Payable, Term Loans P

Bank Note Payable, Term Loans Payable and Senior Notes	12 Months Ended
	Dec. 31, 2020
Bank Note Payable, Term Note Payable and Private Placements
Bank Note Payable, Term Note Payable and Private Placements	4. Bank Note Payable, Term Note Payable and Private Placements ​ JPM Term Loan ​ On August 2, 2018, the Company entered into an Amended and Restated Credit Agreement with JPMorgan Chase Bank, N.A., as administrative agent and lender (“JPMorgan”), and the other lending institutions party thereto (the “JPM Credit Agreement”), which provides a single unsecured bridge loan in the aggregate principal amount of $150 million (the “JPM Term Loan”). On December 24, 2020 the Company repaid a $50 million portion of the JPM Term Loan with a portion of the proceeds from the December 23, 2020 sale of its Durham, North Carolina property, and $100 million remains fully advanced and outstanding under the JPM Term Loan. The JPM Term Loan matures on November 30, 2021, which maturity date may be extended by two additional six-month periods, or until November 30, 2022 (subject to specified exceptions). The JPM Term Loan was previously evidenced by a Credit Agreement, dated November 30, 2016, among the Company, JPMorgan, as administrative agent and lender, and the other lending institutions party thereto, as amended by a First Amendment, dated October 18, 2017. ​ The JPM Term Loan bears interest at either (i) a number of basis points over the LIBOR-based rate depending on the Company’s credit rating (125.0 basis points over the LIBOR-based rate at December 31, 2020) or (ii) a number of basis points over the base rate depending on the Company’s credit rating (25.0 basis points over the base rate at December 31, 2020). ​ The margin over the LIBOR-based rate or base rate is determined based on the Company’s credit rating pursuant to the following grid: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ LIBOR-BASED ​ ​ ​ CREDIT ​ RATE ​ BASE RATE LEVEL ​ RATING ​ MARGIN ​ MARGIN I A- / A3 (or higher) 85.0 bps — bps II ​ BBB+ / Baa1 ​ 90.0 bps — bps III ​ BBB / Baa2 ​ 100.0 bps — bps IV ​ BBB- / Baa3 ​ 125.0 bps 25.0 bps V ​ <BBB- / Baa3 ​ 165.0 bps 65.0 bps ​ For purposes of the JPM Term Loan, base rate means, for any day, a fluctuating rate per annum equal to the greatest of: (i) JPMorgan Chase Bank, N.A.’s prime rate in effect on such day, (ii) the greater of the Federal Funds Rate or the overnight bank funding rate in effect on such day, plus 0.50% (but no less than zero), and (iii) the one month Adjusted LIBOR based rate for a such day plus 1.00% . For purposes of the JPM Term Loan, the LIBOR-based rate means, for any interest period, the LIBOR rate for a period equal in length to the applicable interest period multiplied by the statutory reserve rate. As of December 31, 2020, the Company’s credit rating from Moody’s Investors Service was Baa3. ​ Although the interest rate on the JPM Term Loan is variable under the JPM Credit Agreement, the Company fixed the LIBOR-based rate on a portion of the JPM Term Loan by entering into interest rate swap transactions. On March 7, 2019, the Company entered into ISDA Master Agreements with various financial institutions to hedge a $100 million portion of the future LIBOR-based rate risk under the JPM Credit Agreement. Effective March 29, 2019, the Company fixed the LIBOR-based rate at million portion of the JPM Term Loan until November 30, 2021. Accordingly, based upon the Company’s credit rating, as of December 31, 2020, the effective interest rate on the remaining per annum. ​ The weighted average interest rate on the unhedged $50 million portion of the JPM Term Loan during the year ended December 31, 2020 was approximately 1.90% per annum. The weighted average interest rate on the JPM Term Loan during the year ended December 31, 2019 was approximately per annum. ​ The JPM Credit Agreement contains customary affirmative and negative covenants for credit facilities of this type, including limitations with respect to indebtedness, liens, investments, mergers and acquisitions, disposition of assets, changes in business, certain restricted payments, the requirement to have subsidiaries provide a guaranty in the event that they incur recourse indebtedness and transactions with affiliates. The JPM Credit Agreement also contains financial covenants that require the Company to maintain a minimum tangible net worth, a minimum fixed charge coverage ratio, a maximum secured leverage ratio, a maximum leverage ratio, a maximum unencumbered leverage ratio, and minimum unsecured interest coverage. The JPM Credit Agreement provides for customary events of default with corresponding grace periods, including failure to pay any principal or interest when due, certain cross defaults and a change in control of the Company (as defined in the JPM Credit Agreement). In the event of a default by the Company, the administrative agent may, and at the request of the requisite number of lenders shall, declare all obligations under the JPM Credit Agreement immediately due and payable, and enforce any and all rights of the lenders or administrative agent under the JPM Credit Agreement and related documents. For certain events of default related to bankruptcy, insolvency, and receivership, all outstanding obligations of the Company will become immediately due and payable. The Company was in compliance with the JPM Term Loan financial covenants as of December 31, 2020. ​ BMO Term Loan ​ On September 27, 2018, the Company entered into a Second Amended and Restated Credit Agreement with the lending institutions party thereto and Bank of Montreal (“BMO”), as administrative agent (the “BMO Credit Agreement”). The BMO Credit Agreement provides for a single, unsecured term loan borrowing in the amount of million tranche B term loan. The tranche A term loan matures on November 30, 2021 and the tranche B term loan matures on January 31, 2024. The BMO Credit Agreement also includes an accordion feature that allows up to million of additional loans, subject to receipt of lender commitments and satisfaction of certain customary conditions. The BMO Term Loan was previously evidenced by an Amended and Restated Credit Agreement, dated October 29, 2014, among the Company, BMO, as administrative agent and lender, and the other lending institutions party thereto, as amended by a First Amendment, dated July 21, 2016, and a Second Amendment, dated October 18, 2017. ​ The BMO Term Loan bears interest at either (i) a number of basis points over LIBOR depending on the Company’s credit rating (125 basis points over LIBOR at December 31, 2020) or (ii) a number of basis points over the base rate depending on the Company’s credit rating (25 basis points over the base rate at December 31, 2020). The margin over LIBOR rate or base rate is determined based on the Company’s credit rating pursuant to the following grid: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Credit ​ LIBOR Rate ​ Base Rate ​ Level Rating Margin Margin I ​ A- / A3 (or higher) ​ 85.0 bps — bps II ​ BBB+ / Baa1 ​ ​ 90.0 bps — bps III ​ BBB / Baa2 ​ ​ 100.0 bps — bps IV ​ BBB- / Baa3 ​ ​ 125.0 bps 25.0 bps V ​ <BBB- / Baa3 ​ ​ 165.0 bps 65.0 bps ​ For purposes of the BMO Term Loan, base rate means, for any day, a fluctuating rate per annum equal to the highest of: (i) the bank’s prime rate for such day, (ii) the Federal Funds Rate for such day, plus 0.50%, and (iii) the one month LIBOR based rate for such day plus 1.00%. As of December 31, 2020, the Company’s credit rating from Moody’s Investors Service was Baa3. ​ Although the interest rate on the BMO Term Loan is variable under the BMO Credit Agreement, the Company fixed the base LIBOR interest rate by entering into interest rate swap transactions. On August 26, 2013, the Company entered into an ISDA Master Agreement with Bank of Montreal that fixed the base LIBOR interest rate on the BMO Term Loan at 2.32% per annum, which matured on August 26, 2020. On February 20, 2019, the Company entered into ISDA Master Agreements with a group of banks that fixed the base LIBOR interest rate on the BMO Term Loan at per annum for the period beginning on August 26, 2020 and ending January 31, 2024. Accordingly, based upon the Company’s credit rating, as of December 31, 2020, the effective interest rate on the BMO Term Loan was per annum. ​ The BMO Credit Agreement contains customary affirmative and negative covenants for credit facilities of this type, including limitations with respect to indebtedness, liens, investments, mergers and acquisitions, disposition of assets, changes in business, certain restricted payments, the requirement to have subsidiaries provide a guaranty in the event that they incur recourse indebtedness and transactions with affiliates. The BMO Credit Agreement also contains financial covenants that require the Company to maintain a minimum tangible net worth, a maximum leverage ratio, a maximum secured leverage ratio, a minimum fixed charge coverage ratio, a maximum unencumbered leverage ratio, and minimum unsecured interest coverage. The BMO Credit Agreement provides for customary events of default with corresponding grace periods, including failure to pay any principal or interest when due, certain cross defaults and a change in control of the Company (as defined in the BMO Credit Agreement). In the event of a default by the Company, the administrative agent may, and at the request of the requisite number of lenders shall, declare all obligations under the BMO Credit Agreement immediately due and payable, terminate the lenders’ commitments to make loans under the BMO Credit Agreement, and enforce any and all rights of the lenders or administrative agent under the BMO Credit Agreement and related documents. For certain events of default related to bankruptcy, insolvency, and receivership, the commitments of lenders will be automatically terminated and all outstanding obligations of the Company will become immediately due and payable. The Company was in compliance with the BMO Term Loan financial covenants as of December 31, 2020. ​ BAML Credit Facility ​ On July 21, 2016, the Company entered into a First Amendment (the “BAML First Amendment”), and on October 18, 2017, the Company entered into a Second Amendment (the “BAML Second Amendment”), to the Second Amended and Restated Credit Agreement dated October 29, 2014 among the Company, the lending institutions party thereto and Bank of America, N.A., as administrative agent, L/C Issuer and Swing Line Lender (as amended by the BAML First Amendment and the BAML Second Amendment, the “BAML Credit Facility”) that continued an existing unsecured revolving line of credit (the “BAML Revolver”) and extended the maturity of a term loan (the “BAML Term Loan”). ​ BAML Revolver Highlights ​ ● The BAML Revolver is for borrowings, at the Company's election, of up to $600 million. Borrowings made pursuant to the BAML Revolver may be revolving loans, swing line loans or letters of credit, the combined sum of which may not exceed $600 million outstanding at any time. ● Borrowings made pursuant to the BAML Revolver may be borrowed, repaid and reborrowed from time to time until the initial maturity date of January 12, 2022. The Company has the right to extend the maturity date of the BAML Revolver by two additional six month periods, or until January 12, 2023, upon payment of a fee and satisfaction of certain customary conditions. ● The BAML Credit Facility includes an accordion feature that allows for an aggregate amount of up to $500 million of additional borrowing capacity applicable to the BAML Revolver and/or the BAML Term Loan subject to receipt of lender commitments and satisfaction of certain customary conditions. ​ As of December 31, 2020 and December 31, 2019, there were $3.5 million and no borrowings outstanding under the BAML Revolver, respectively. The BAML Revolver bears interest at either (i) a margin over LIBOR depending on the Company’s credit rating ( ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Base ​ ​ ​ ​ ​ LIBOR Rate ​ Facility ​ Rate ​ Level Credit Rating Margin Fee Margin I A- / A3 (or higher) 0.825 % 0.125 % 0.000 % II BBB+ / Baa1 ​ 0.875 % 0.150 % 0.000 % III BBB / Baa2 ​ 1.000 % 0.200 % 0.000 % IV BBB- / Baa3 ​ 1.200 % 0.250 % 0.200 % V <BBB- / Baa3 ​ 1.550 % 0.300 % 0.550 % ​ For purposes of the BAML Credit Facility, base rate means, for any day, a fluctuating rate per annum equal to the highest of: (i) the bank’s prime rate for such day, (ii) the Federal Funds Rate for such day, plus 0.50%, and (iii) the one month LIBOR based rate for such day plus 1.00%. As of December 31, 2020, the Company’s credit rating from Moody’s Investors Service was Baa3. ​ Based upon the Company’s credit rating, as of December 31, 2020, the interest rate on the BAML Revolver was 1.34% per annum. The weighted average interest rate on all amounts outstanding on the BAML Revolver during the year ended December 31, 2020 was approximately per annum. The weighted average interest rate on all amounts outstanding on the BAML Revolver during the year ended December 31, 2019 was approximately per annum. ​ BAML Term Loan Highlights ​ ● The BAML Term Loan is for $400 million. ● The BAML Term Loan matures on January 12, 2023. ● The BAML Credit Facility includes an accordion feature that allows for an aggregate amount of up to $500 million of additional borrowing capacity applicable to the BAML Revolver and/or the BAML Term Loan subject to receipt of lender commitments and satisfaction of certain customary conditions. ● On September 27, 2012, the Company drew down the entire $400 million under the BAML Term Loan and such amount remains fully advanced and outstanding under the BAML Term Loan. ​ The BAML Term Loan bears interest at either (i) a margin over LIBOR depending on the Company’s credit rating ( (0.35% over the base rate at December 31, 2020). The margin over LIBOR rate or base rate is determined based on the Company’s credit rating pursuant to the following grid: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ LIBOR Rate ​ Base Rate ​ Level Credit Rating Margin Margin I A- / A3 (or higher) 0.900 % 0.000 % II BBB+ / Baa1 ​ 0.950 % 0.000 % III BBB / Baa2 ​ 1.100 % 0.100 % IV BBB- / Baa3 ​ 1.350 % 0.350 % V <BBB- / Baa3 ​ 1.750 % 0.750 % ​ For purposes of the BAML Credit Facility, base rate means, for any day, a fluctuating rate per annum equal to the highest of: (i) the bank’s prime rate for such day, (ii) the Federal Funds Rate for such day, plus 0.50%, and (iii) the one month LIBOR based rate for such day plus 1.00% . As of December 31, 2020, the Company’s credit rating from Moody’s Investors Service was Baa3. ​ Although the interest rate on the BAML Credit Facility is variable, the Company fixed the base LIBOR interest rate on the BAML Term Loan by entering into interest rate swap transactions. On July 22, 2016, the Company entered into ISDA Master Agreements with a group of banks that fixed the base LIBOR interest rate on the BAML Term Loan at per annum for the period beginning on September 27, 2017 and ending on September 27, 2021. Accordingly, based upon the Company’s credit rating, as of December 31, 2020, the effective interest rate on the BAML Term Loan was per annum. ​ BAML Credit Facility General Information ​ The BAML Credit Facility contains customary affirmative and negative covenants for credit facilities of this type, including limitations with respect to indebtedness, liens, investments, mergers and acquisitions, disposition of assets, changes in business, certain restricted payments, the requirement to have subsidiaries provide a guaranty in the event that they incur recourse indebtedness and transactions with affiliates. The BAML Credit Facility also contains financial covenants that require the Company to maintain a minimum tangible net worth, a maximum leverage ratio, a maximum secured leverage ratio, a minimum fixed charge coverage ratio, a maximum unencumbered leverage ratio, and minimum unsecured interest coverage. The BAML Credit Facility provides for customary events of default with corresponding grace periods, including failure to pay any principal or interest when due, certain cross defaults and a change in control of the Company (as defined in the BAML Credit Facility). In the event of a default by the Company, the administrative agent may, and at the request of the requisite number of lenders shall, declare all obligations under the BAML Credit Facility immediately due and payable, terminate the lenders’ commitments to make loans under the BAML Credit Facility, and enforce any and all rights of the lenders or administrative agent under the BAML Credit Facility and related documents. For certain events of default related to bankruptcy, insolvency, and receivership, the commitments of lenders will be automatically terminated and all outstanding obligations of the Company will become immediately due and payable. The Company was in compliance with the BAML Credit Facility financial covenants as of December 31, 2020. ​ The Company may use the proceeds of the loans under the BAML Credit Facility to finance the acquisition of real properties and for other permitted investments; to finance investments associated with Sponsored REITs, to refinance or retire indebtedness and for working capital and other general business purposes, in each case to the extent permitted under the BAML Credit Facility. ​ Senior Notes ​ On October 24, 2017, the Company entered into a note purchase agreement (the “Note Purchase Agreement”) with the various purchasers named therein (the “Purchasers”) in connection with a private placement of senior unsecured notes. Under the Note Purchase Agreement, the Company agreed to sell to the Purchasers an aggregate principal amount of $200,000,000 of senior unsecured notes consisting of (i) 3.99% Series A Senior Notes due December 20, 2024 in an aggregate principal amount of $116 million (the “Series A Notes”) and (ii) 4.26% Series B Senior Notes due December 20, 2027 in an aggregate principal amount of $84 million (the “Series B Notes,” and, together with the Series A Notes, the “Senior Notes”). On December 20, 2017, the Senior Notes were funded and the proceeds were used to reduce the outstanding balance of the BAML Revolver. ​ The Note Purchase Agreement contains customary financial covenants, including a maximum leverage ratio, a maximum secured leverage ratio, a minimum fixed charge coverage ratio, and a maximum unencumbered leverage ratio. The Note Purchase Agreement also contains restrictive covenants that, among other things, restrict the ability of the Company and its subsidiaries to enter into transactions with affiliates, merge, consolidate, create liens, make certain restricted payments, enter into certain agreements or prepay certain indebtedness. Such financial and restrictive covenants are substantially similar to the corresponding covenants contained in the BAML Credit Facility, the BMO Credit Agreement and the JPM Credit Agreement. The Senior Notes financial covenants require, among other things, the maintenance of a fixed charge coverage ratio of at least 1.50; a maximum leverage ratio and an unsecured leverage ratio of no more than 60% (65% if there were a significant acquisition for a short period of time). In addition, the Note Purchase Agreement provides that the Note Purchase Agreement will automatically incorporate additional financial and other specified covenants (such as limitations on investments and distributions) that are effective from time to time under the existing credit agreements, other material indebtedness or certain other private placements of debt of the Company and its subsidiaries. The Note Purchase Agreement contains customary events of default, including payment defaults, cross defaults with certain other indebtedness, breaches of covenants and bankruptcy events. In the case of an event of default, the Purchasers may, among other remedies, accelerate the payment of all obligations. The Company was in compliance with the Senior Notes financial covenants as of December 31, 2020.

Financial Instruments_ Derivati

Financial Instruments: Derivatives and Hedging	12 Months Ended
	Dec. 31, 2020
Financial Instruments: Derivatives and Hedging
Financial Instruments: Derivatives and Hedging	5. Financial Instruments: Derivatives and Hedging ​ On July 22, 2016, the Company fixed the interest rate for the period beginning on September 27, 2017 and ending on September 27, 2021 on the BAML Term Loan (the “2017 Interest Rate Swap”). On March 7, 2019, the Company fixed the interest rate for the period beginning on March 29, 2019 and ending on November 30, 2021 on a million portion of the JPM Term Loan (the “2019 JPM Interest Rate Swap”). On February 20, 2019, the Company fixed the interest rate for the period beginning August 26, 2020 and ending January 31, 2024 on the BMO Term Loan (the “2019 BMO Interest Rate Swap”). The variable rates that were fixed under the 2017 Interest Rate Swap, the 2019 JPM Interest Rate Swap and the 2019 BMO Interest Rate Swap (collectively referred to as the “Interest Rate Swaps”) are described in Note 4. ​ The Interest Rate Swaps qualify as cash flow hedges and have been recognized on the consolidated balance sheets at fair value. If a derivative qualifies as a hedge, depending on the nature of the hedge, changes in the fair value of the derivative will either be offset against the change in fair value of the hedged asset, liability, or firm commitment through earnings, or recognized in other comprehensive income until the hedged item is recognized in earnings. The ineffective portion of a derivative’s change in fair value will be recognized in earnings in the same period in which the hedged interest payments affect earnings, which may increase or decrease reported net income and stockholders’ equity prospectively, depending on future levels of interest rates and other variables affecting the fair values of derivative instruments and hedged items, but will have no effect on cash flows. ​ The following table summarizes the notional and fair value of our derivative financial instruments at December 31, 2020. The notional value is an indication of the extent of our involvement in these instruments at that time, but does not represent exposure to credit, interest rate or market risks. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Notional Strike Effective Expiration Fair Value (2) at December 31, (in thousands) ​ Value ​ Rate ​ Date ​ Date ​ 2020 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2017 Interest Rate Swap ​ $ 400,000 1.12 % Sep-17 Sep-21 ​ $ (2,947) ​ $ 3,022 ​ 2019 JPM Interest Rate Swap ​ $ 100,000 2.44 % Mar-19 Nov-21 ​ $ (2,102) ​ $ (1,634) ​ 2019 BMO Interest Rate Swap (1) ​ $ 220,000 2.39 % Aug-20 Jan-24 ​ $ (12,262) ​ $ (5,107) ​ 2013 BMO Interest Rate Swap ​ $ 220,000 2.32 % Aug-13 Aug-20 ​ $ — ​ $ (963) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (1) The Notional Value will decrease to $165 million on November 30, 2021. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (2) Classified within Level 2 of the fair value hierarchy. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ On December 31, 2020, the 2017 Interest Rate Swap, 2019 JPM Interest Rate Swap and 2019 BMO Interest Rate Swap were reported as liabilities with an aggregate fair value of approximately $17.3 million and are included in other liabilities: derivative liabilities in the consolidated balance sheet at December 31, 2020. ​ The gain/(loss) on the Company’s Interest Rate Swaps that was recorded in OCI and the accompanying consolidated statements of income as a component of interest expense for the years ended December 31, 2020, 2019 and 2018, respectively, was as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ Year Ended December 31, Interest Rate Swaps in Cash Flow Hedging Relationships: 2020 2019 2018 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Amounts of gain (loss) recognized in OCI ​ $ (20,380) ​ $ (15,119) ​ $ 5,321 Amounts of previously recorded gain/(loss) reclassified from OCI into Interest Expense ​ $ (7,751) ​ $ 4,328 ​ $ 2,722 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total amount of Interest Expense presented in the consolidated statements of operations ​ $ 36,026 ​ $ 36,757 ​ $ 38,374 ​ Over time, the unrealized gains and losses held in accumulated other comprehensive income will be reclassified into earnings as an increase or reduction to interest expense in the same periods in which the hedged interest payments affect earnings. The Company estimates that approximately ​ The Company is hedging the exposure to variability in anticipated future interest payments on existing debt. ​ The BMO Term Loan, BAML Term Loan and JPM Term Loan hedging transactions used derivative instruments that involve certain additional risks such as counterparty credit risk, the enforceability of hedging contracts and the risk that unanticipated and significant changes in interest rates will cause a significant loss of basis in either or both of the contracts. The Company requires its derivatives contracts to be with counterparties that have investment grade ratings. As a result, the Company does not anticipate that any counterparty will fail to meet its obligations. However, there can be no assurance that the Company will be able to adequately protect against the foregoing risks or that it will ultimately realize an economic benefit that exceeds the related amounts incurred in connection with engaging in such hedging strategies. ​ The fair value of the Company’s derivative instruments are determined using the net discounted cash flows of the expected cash flows of the derivative based on the market based interest rate curve and are adjusted to reflect credit or nonperformance risk. The risk is estimated by the Company using credit spreads and risk premiums that are observable in the market. These financial instruments were classified within Level 2 of the fair value hierarchy and were classified as an asset or liability on the consolidated balance sheets. ​ The Company’s derivatives are recorded at fair value in other assets: derivative asset and other liabilities: derivative liability in the consolidated balance sheets and the effective portion of the derivatives’ fair value is recorded to other comprehensive income in the consolidated statements of other comprehensive income (loss) and prior to January 1, 2019, the ineffective portion of the derivatives’ fair value was recognized directly into earnings as other in the consolidated statements of income. ​

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2020
Stockholders' Equity
Stockholders' Equity	6. Stockholders’ Equity ​ Equity-Based Compensation ​ On May 20, 2002, the stockholders of the Company approved the 2002 Stock Incentive Plan (the “Plan”). The Plan is an equity-based incentive compensation plan, and provides for the grants of up to a maximum of 2,000,000 shares of the Company’s common stock (“Awards”). All of the Company’s employees, officers, directors, consultants and advisors are eligible to be granted Awards. Awards under the Plan are made at the discretion of the Company’s Board of Directors, and have no vesting requirements. Upon granting an Award, the Company will recognize compensation cost equal to the fair value of the Company’s common stock, as determined by the Company’s Board of Directors, on the date of the grant. The Company granted 55,572 shares under the Plan between 2002 and 2005 and made no grants between 2006 and 2018. ​ On June 4, 2020 and December 10, 2019, the Company granted 58,998 and 38,046 shares, respectively, under the Plan to non-employee directors at a compensation cost of approximately $337,000 at each grant date, which is included in general and administrative expenses in the consolidated statements of income. Such shares were fully vested on the date of issuance. There are currently shares available for grant under the Plan. ​ ​ ​ ​ ​ ​ ​ ​ ​ Shares Available ​ Compensation (in thousands) ​ for Grant ​ Cost ​ ​ ​ ​ ​ ​ ​ Balance, December 31, 2016, 2017 and 2018 ​ ​ 1,944,428 ​ ​ ​ Shares granted 2019 ​ ​ (38,046) ​ $ 337,000 Balance December 31, 2019 ​ ​ 1,906,382 ​ ​ 337,000 Shares granted 2020 ​ ​ (58,998) ​ ​ 337,000 Balance December 31, 2020 ​ ​ 1,847,384 ​ $ 674,000 ​

Federal Income Tax Reporting

Federal Income Tax Reporting	12 Months Ended
	Dec. 31, 2020
Federal Income Tax Reporting
Federal Income Tax Reporting	7. Federal Income Tax Reporting ​ General ​ The Company has elected to be taxed as a REIT under the Internal Revenue Code of 1986, as amended (the “Code”). As a REIT, the Company generally is entitled to a tax deduction for distributions paid to its shareholders, thereby effectively subjecting the distributed net income of the Company to taxation at the shareholder level only. The Company must comply with a variety of restrictions to maintain its status as a REIT. These restrictions include the type of income it can earn, the type of assets it can hold, the number of shareholders it can have and the concentration of their ownership, and the amount of the Company’s taxable income that must be distributed annually. ​ One such restriction is that the Company generally cannot own more than 10% of the voting power or value of the securities of any one issuer unless the issuer is itself a REIT or a taxable REIT subsidiary (“TRS”). In the case of TRSs, the Company’s ownership of securities in all TRSs generally cannot exceed of the value of all of the Company’s assets. FSP Investments LLC and FSP Protective TRS Corp. are the Company’s taxable REIT subsidiaries operating as taxable corporations under the Code. The TRSs have gross amounts of net operating losses (“NOLs”) available to those taxable corporations of million and million as of each of December 31, 2020 and 2019, respectively. The NOLs created prior to 2018 will expire between 2030 and 2047 and the NOLs generated after 2017 will not expire. A valuation allowance is provided for the full amount of the NOLs as the realization of any tax benefits from such NOLs is not assured. ​ Income taxes are recorded based on the future tax effects of the difference between the tax and financial reporting bases of the Company’s assets and liabilities. In estimating future tax consequences, potential future events are considered except for potential changes in income tax law or in rates. ​ The Company adopted an accounting pronouncement related to uncertainty in income taxes effective January 1, 2007, which did not result in recording a liability, nor was any accrued interest and penalties recognized with the adoption. Accrued interest and penalties will be recorded as income tax expense if the Company records a liability in the future. The Company’s effective tax rate was not affected by the adoption. The Company and one or more of its subsidiaries files income tax returns in the U.S. federal jurisdiction and various state jurisdictions. The statute of limitations for the Company’s income tax returns is generally three years and as such, the Company’s returns that remain subject to examination would be primarily from 2017 and thereafter. ​ The Company is subject to a business tax known as the Revised Texas Franchise Tax. Some of the Company’s leases allow reimbursement by tenants for these amounts because the Revised Texas Franchise Tax replaces a portion of the property tax for school districts. Because the tax base on the Revised Texas Franchise Tax is derived from an income based measure, it is considered an income tax. The Company recorded a provision for the Revised Texas Franchise Tax of million for the years ended December 31, 2020, 2019 and 2018, respectively. ​ Net operating losses ​ Section 382 of the Code restricts a corporation’s ability to use net operating losses (“NOLs”) to offset future taxable income following certain “ownership changes.” Such ownership changes occurred with past mergers and accordingly a portion of the NOLs incurred by the Sponsored REITs available for use by the Company in any particular future taxable year will be limited. To the extent that the Company does not utilize the full amount of the annual NOLs limit, the unused amount may be carried forward to offset taxable income in future years. NOLs expire 20 years after the year in which they arise, and the last of the Company’s NOLs will expire in 2027. A valuation allowance is provided for the full amount of the NOLs as the realization of any tax benefits from such NOLs is not assured. The gross amount of NOLs available to the Company was $13.0 million as of each of December 31, 2020, 2019 and 2018. ​ Income Tax Expense ​ The income tax expense reflected in the consolidated statements of income relates primarily the Revised Texas Franchise Tax. FSP Protective TRS Corp. provides taxable services to tenants at some of the Company’s properties and the tax expense associated with these activities are reported as Other Taxes in the table below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Year Ended December 31, (Dollars in thousands) 2020 2019 2018 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revised Texas Franchise Tax ​ $ 250 ​ $ 394 ​ $ 319 ​ Other Taxes ​ — ​ (125) ​ 41 ​ Tax expense ​ $ 250 ​ $ 269 ​ $ 360 ​ ​ Taxes on income are a current tax expense. No deferred income taxes were provided as there were no material temporary differences between the financial reporting basis and the tax basis of the TRSs. ​ At December 31, 2020, the Company’s net tax basis of its real estate assets is more than the amount set forth in the Company’s consolidated balance sheets by $253.0 million and at December 31, 2019, the Company’s net tax basis of its real estate assets is more than the amount set forth in the Company’s consolidated balance sheets by $195.0 million. ​ Reconciliation Between GAAP Net Income and Taxable Income ​ The following reconciles GAAP net income to taxable income for the years ended December 31, 2020, 2019 and 2018. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the year ended December 31, (in thousands) 2020 2019 2018 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income per GAAP ​ $ 32,615 ​ $ 6,475 ​ $ 13,069 ​ Adjustments to GAAP net income: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ GAAP depreciation and amortization ​ 88,244 ​ 90,507 ​ 93,675 ​ Tax depreciation and amortization ​ (79,542) ​ (66,376) ​ (62,657) ​ Tax basis more than GAAP basis on assets sold ​ (11,450) ​ — ​ — ​ Straight line rent adjustment, net ​ (1,685) ​ (10,462) ​ (1,350) ​ Deferred rent, net ​ 1,956 ​ 535 ​ 210 ​ Non-taxable distributions ​ — ​ — ​ (710) ​ Other, net ​ 390 ​ 4,099 ​ (6,651) ​ Taxable income ​ 30,528 ​ 24,778 ​ 35,586 ​ Less: Capital gains recognized ​ 7,576 ​ — ​ — ​ Taxable income subject to distribution requirement ​ $ 22,952 ​ $ 24,778 ​ $ 35,586 ​ ​ Tax Components ​ The following summarizes the tax components of the Company’s common distributions paid per share for the years ended December 31, 2020, 2019 and 2018: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ 2019 ​ 2018 ​ Per Share % Per Share % Per Share % Ordinary income (1) ​ $ 0.28 77.51 % $ 0.25 69.96 % $ 0.35 76.39 % Capital gain ​ 0.06 16.72 % — — % — — % Return of capital ​ 0.02 5.77 % 0.11 30.04 % 0.11 23.61 % Total ​ $ 0.36 100 % $ 0.36 100 % $ 0.46 100 % ​ (1) The 2019 Ordinary income amount includes a qualified distribution, which is a subset of, and included in, the ordinary income amount and is $0.009 per share or 2.52% of total distributions.

Leases

Leases	12 Months Ended
	Dec. 31, 2020
Leases
Leases	8. Leases ​ Leases as a Lessee: ​ The Company entered into a noncancelable contract with a third party to obtain office space that commenced on September 1, 2010. The contract was amended on October 25, 2016 to extend the contract through September 30, 2024. As of December 31, 2020, the Company’s right-of-use asset was $1.4 million, which is included in prepaid and other assets on the consolidated balance sheet as of December 31, 2020. ​ The Company has an option to extend the terms of its office space lease with one 5-year extension option. As of December 31, 2020, the exercise of the extension option was not reasonably certain. Therefore, the extension option is not recognized as part of the Company’s right-of-use asset and lease liability. ​ A discount rate equal to the Company’s incremental borrowing rate was applied to the future monthly contractual lease payments remaining as of December 31, 2020 to compute the lease liability. The incremental borrowing rate is the rate equal to the closest borrowing under the BAML Revolver at the time of the Company’s adoption of ASU 2016-02. ​ ​ ​ ​ ​ ​ ​ Lease Costs ​ ​ ​ ​ ​ Year Ended (in thousands) ​ December 31, 2020 ​ December 31, 2019 Operating lease cost $ 419 ​ $ 419 ​ $ 419 ​ $ 419 ​ ​ ​ ​ ​ ​ Other information ​ ​ ​ ​ ​ Cash paid for amounts included in the measurement of lease liabilities ​ 421 ​ ​ 412 Weighted average remaining lease terms in years - operating leases ​ 3.75 ​ ​ 4.75 Weighted average discount rate - operating leases ​ 3.86% ​ ​ 3.86% ​ ​ ​ ​ ​ ​ Maturity analysis for liabilities Total ​ ​ ​ Undiscounted ​ ​ ​ (in thousands) Cash Flows ​ ​ ​ Discount rate at commencement ​ 3.86% ​ ​ ​ 2021 $ 429 ​ ​ ​ 2022 ​ 438 ​ ​ ​ 2023 ​ 447 ​ ​ ​ 2024 ​ 340 ​ ​ ​ ​ $ 1,654 ​ ​ ​ ​ ​ ​ ​ ​ ​ Present value lease liability $ 1,536 ​ ​ ​ ​ ​ ​ ​ ​ ​ Difference between undiscounted cash flows and discounted cash flows $ 118 ​ ​ ​ ​ Leases as a Lessor: ​ The Company is a lessor of commercial real estate with operations that include the leasing of office and industrial properties. Many of the leases with customers contain options to extend leases at a fair market rate and may also include options to terminate leases. The Company considers several inputs when evaluating the amount it expects to derive from its leased assets at the end of the lease terms, such as the remaining useful life, expected market conditions, fair value of lease payments, expected fair values of underlying assets, and expected deployment of the underlying assets. The Company’s strategy to address its risk for the residual value in its commercial real estate is to re-lease the commercial space. ​ The Company has elected to apply the practical expedient to not separate non-lease components from the related lease component of real estate leases. This combined component is primarily comprised of fixed lease payments, early termination fees, common area maintenance cost reimbursements, and parking lease payments. The Company applies ASC 842-Leases to the combined lease and non-lease components. ​ A minority of the Company’s leases are subject to annual changes in the Consumer Price Index (“CPI”). Although increases in the CPI are not estimated as part of the Company’s measurement of straight-line rent revenue, to the extent that the actual CPI is greater or less than the CPI at lease commencement, there could be changes to realized income or loss. ​ For the year ended December 31, 2020 and 2019, the Company recognized the following amounts of income relating to lease payments: ​ ​ ​ ​ ​ ​ ​ ​ Income relating to lease payments: ​ ​ ​ ​ Year Ended (in thousands) December 31, 2020 December 31, 2019 Income from leases (1) ​ $ 242,209 ​ $ 256,250 ​ ​ $ 242,209 ​ $ 256,250 ​ ​ ​ ​ ​ ​ ​ Undiscounted Cash Flows Year ending ​ ​ ​ (in thousands) ​ December 31, ​ ​ ​ 2021 ​ ​ 162,676 ​ ​ ​ 2022 ​ ​ 146,031 ​ ​ ​ 2023 ​ ​ 138,363 ​ ​ ​ 2024 ​ ​ 127,269 ​ ​ ​ 2025 ​ ​ 107,596 ​ ​ ​ 2026 and thereafter ​ 361,423 ​ ​ ​ ​ ​ $ 1,043,358 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (1) Amounts recognized from variable lease payments were variable lease payments $61,310 and $64,421 for the years ended December 31, 2020 and 2019, respectively. ​ ​ ​ ​ ​ ​ ​

Retirement Plan

Retirement Plan	12 Months Ended
	Dec. 31, 2020
Retirement Plan
Retirement Plan	9. Retirement Plan ​ In 2006, the Company established a 401(k) plan to cover eligible employees, which permitted deferral of up to $17,000 per year (indexed for inflation) into the 401(k) plan, subject to certain limitations imposed by the Internal Revenue Code. An employee’s elective deferrals are immediately vested upon contribution to the 401(k) plan. The Company matches employee contributions to the 401(k) plan dollar for dollar up to 3% of each employee’s annual compensation up to $200,000. In addition, we may elect to make an annual discretionary profit-sharing contribution. The Company’s total contribution under the 401(k) plan amounted to $0.1 million, $0.2 million and $0.1 million for the years ended December 31, 2020, 2019 and 2018, respectively.

Dispositions of Property

Dispositions of Property	12 Months Ended
	Dec. 31, 2020
Dispositions of property
Dispositions of properties	10. Dispositions of Property ​ The Company sold an office property located in Durham, North Carolina on December 23, 2020 with a sales price of approximately $89.7 million, at a gain of approximately $41.9 million. ​ ​ ​

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2020
Subsequent Events
Subsequent Events	11. Subsequent Events ​ On January 15, 2021, the Board of Directors of the Company declared a cash distribution of $0.09 per share of common stock payable on February 18, 2021 to stockholders of record on January 29, 2021. ​

Selected Unaudited Quarterly In

Selected Unaudited Quarterly Information	12 Months Ended
	Dec. 31, 2020
Selected Unaudited Quarterly Information
Selected Unaudited Quarterly Information	12. Selected Unaudited Quarterly Information ​ Selected unaudited quarterly information is shown in the following table: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ First Second Third Fourth ​ ​ Quarter ​ Quarter ​ Quarter ​ Quarter ​ ​ (in thousands, except per share data) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenue ​ $ 62,983 ​ $ 60,808 ​ $ 62,247 ​ $ 59,810 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) ​ $ (1,071) ​ $ (2,075) ​ $ (1,679) ​ $ 37,440 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basic and diluted net income (loss) per share ​ $ (0.01) ​ $ (0.02) ​ $ (0.02) ​ $ 0.35 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average number of shares outstanding ​ 107,269 ​ 107,287 ​ 107,328 ​ 107,328 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 ​ First Second Third Fourth ​ ​ Quarter ​ Quarter ​ Quarter ​ Quarter ​ ​ (in thousands, except per share data) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenue ​ $ 64,716 ​ $ 66,813 ​ $ 68,539 ​ $ 68,997 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) ​ $ (1,205) ​ $ 1,633 ​ $ 2,399 ​ $ 3,648 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basic and diluted net income (loss) per share ​ $ (0.01) ​ $ 0.02 ​ $ 0.02 ​ $ 0.03 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average number of shares outstanding ​ 107,231 ​ 107,231 ​ 107,231 ​ 107,240 ​ ​

Schedule II Valuation and quali

Schedule II Valuation and qualifying accounts	12 Months Ended
	Dec. 31, 2020
Schedule II Valuation and qualifying accounts:
Schedule II Valuation and qualifying accounts:	Schedule II ​ Franklin Street Properties Corp. Valuation and qualifying accounts: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Additions ​ ​ ​ ​ ​ ​ ​ (Decreases) ​ ​ ​ ​ ​ ​ ​ ​ Balance at ​ charged to ​ ​ ​ ​ Balance (in thousands) ​ beginning ​ costs and ​ ​ ​ ​ at end Classification ​ of year ​ expenses ​ Deductions ​ of year ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Allowance for doubtful accounts ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2018 ​ $ 250 ​ $ 128 ​ $ (178) ​ $ 200 ​ 2019 ​ 200 ​ 213 ​ (113) ​ 300 ​ 2020 ​ 300 ​ 340 ​ (135) ​ 505 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Straight-line rent allowance for doubtful accounts ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2018 ​ $ 50 ​ $ — ​ $ — ​ $ 50 ​ 2019 ​ 50 ​ — ​ — ​ 50 ​ 2020 ​ 50 ​ — ​ (50) ​ — ​ ​

SCHEDULE III REAL ESTATE AND AC

SCHEDULE III REAL ESTATE AND ACCUMULATED DEPRECIATION	12 Months Ended
	Dec. 31, 2020
SCHEDULE III REAL ESTATE AND ACCUMULATED DEPRECIATION
SCHEDULE III REAL ESTATE AND ACCUMULATED DEPRECIATION	SCHEDULE III FRANKLIN STREET PROPERTIES CORP. REAL ESTATE AND ACCUMULATED DEPRECIATION December 31, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Initial Cost ​ Historical Cost ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Costs ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Capitalized ​ ​ ​ ​ Buildings ​ ​ ​ ​ ​ ​ ​ Total Costs, ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Buildings ​ (Disposals) ​ ​ ​ ​ Improvements ​ ​ ​ ​ ​ ​ ​ Net of ​ Depreciable ​ ​ ​ Date of ​ ​ Encumbrances ​ ​ ​ ​ Improvements ​ Subsequent to ​ ​ ​ ​ and ​ ​ ​ ​ Accumulated ​ Accumulated ​ Life ​ Year ​ Acquisition Description ​ (1) ​ Land ​ and Equipment ​ Acquisition ​ Land ​ Equipment ​ Total (2) ​ Depreciation ​ Depreciation ​ Years ​ Built ​ (3) ​ ​ (in thousands) Commercial Properties: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Forest Park, Charlotte, NC ​ — ​ $ 1,559 ​ $ 5,672 ​ $ 843 ​ $ 1,559 ​ $ 6,515 ​ $ 8,074 ​ 2,197 ​ $ 5,877 5 - 39 1999 1999 ​ Meadow Point, Chantilly, VA ​ — ​ 2,634 ​ 18,911 ​ 8,214 ​ 2,634 ​ 27,125 ​ 29,759 ​ 14,512 ​ 15,247 5 - 39 1999 2001 ​ Timberlake, Chesterfield, MO — ​ 2,984 ​ 38,661 ​ 10,549 ​ 2,984 ​ 49,210 ​ 52,194 ​ 23,645 ​ 28,549 5 - 39 1999 2001 ​ Northwest Point, Elk Grove Village, IL — ​ 2,914 ​ 26,295 ​ 12,401 ​ 2,914 ​ 38,696 ​ 41,610 ​ 19,497 ​ 22,113 5 - 39 1999 2001 ​ Timberlake East, Chesterfield, MO — ​ 2,626 ​ 17,608 ​ 5,377 ​ 2,626 ​ 22,985 ​ 25,611 ​ 11,052 ​ 14,559 5 - 39 2000 2002 ​ Park Ten, Houston, TX — ​ 1,061 ​ 21,303 ​ 6,899 ​ 567 ​ 28,696 ​ 29,263 ​ 13,225 ​ 16,038 5 - 39 1999 2002 ​ Addison, Addison, TX — ​ 4,325 ​ 48,040 ​ 12,106 ​ 4,325 ​ 60,146 ​ 64,471 ​ 23,625 ​ 40,846 5 - 39 1999 2002 ​ Collins, Richardson, TX — ​ 4,000 ​ 42,598 ​ 8,497 ​ 4,000 ​ 51,095 ​ 55,095 ​ 23,307 ​ 31,788 5 - 39 1999 2003 ​ Greenwood, Englewood, CO — ​ 3,100 ​ 30,201 ​ 11,770 ​ 3,100 ​ 41,971 ​ 45,071 ​ 18,663 ​ 26,408 5 - 39 2000 2005 ​ River Crossing, Indianapolis, IN — ​ 3,000 ​ 36,926 ​ 6,448 ​ 3,000 ​ 43,374 ​ 46,374 ​ 16,740 ​ 29,634 5 - 39 1998 2005 ​ Innsbrook, Glenn Allen, VA — ​ 5,000 ​ 40,216 ​ 8,945 ​ 5,000 ​ 49,161 ​ 54,161 ​ 19,141 ​ 35,020 5 - 39 1999 2003 ​ 380 Interlocken, Bloomfield, CO — ​ 8,275 ​ 34,462 ​ 12,624 ​ 8,275 ​ 47,086 ​ 55,361 ​ 17,122 ​ 38,239 5 - 39 2000 2003 ​ Blue Lagoon, Miami, FL — ​ 6,306 ​ 46,124 ​ 18,068 ​ 6,306 ​ 64,192 ​ 70,498 ​ 14,998 ​ 55,500 5 - 39 2002 2003 ​ Eldridge Green, Houston, TX — ​ 3,900 ​ 43,791 ​ 5,548 ​ 3,900 ​ 49,339 ​ 53,239 ​ 19,925 ​ 33,314 5 - 39 1999 2004 ​ Liberty Plaza, Addison, TX — ​ 4,374 ​ 21,146 ​ 8,976 ​ 4,374 ​ 30,122 ​ 34,496 ​ 12,090 ​ 22,406 5 - 39 1985 2006 ​ One Overton, Atlanta, GA — ​ 3,900 ​ 77,229 ​ 17,781 ​ 3,900 ​ 95,010 ​ 98,910 ​ 37,025 ​ 61,885 5 - 39 2002 2006 ​ 390 Interlocken, Broomfield, CO — ​ 7,013 ​ 37,751 ​ 14,197 ​ 7,013 ​ 51,948 ​ 58,961 ​ 18,480 ​ 40,481 5 - 39 2002 2006 ​ Park Ten II, Houston, TX — ​ 1,300 ​ 31,712 ​ 6,979 ​ 1,300 ​ 38,691 ​ 39,991 ​ 11,764 ​ 28,227 5 - 39 2006 2006 ​ Dulles Virginia, Sterling, VA — ​ 4,813 ​ 13,285 ​ 6,714 ​ 4,813 ​ 19,999 ​ 24,812 ​ 7,295 ​ 17,517 5 - 39 1999 2008 ​ Stonecroft, Chantilly, VA — ​ 2,102 ​ 18,003 ​ 1,814 ​ 2,102 ​ 19,817 ​ 21,919 ​ 5,116 ​ 16,803 5 - 39 2008 2009 ​ 121 South Eight Street, Minneapolis, MN — ​ 4,444 ​ 15,214 ​ 24,592 ​ 4,444 ​ 39,806 ​ 44,250 ​ 10,917 ​ 33,333 5 - 39 1974 2010 ​ 801 Marquette Ave South, Minneapolis, MN ​ — ​ 4,184 ​ — ​ 22,295 ​ 4,184 ​ 22,295 ​ 26,479 ​ 1,836 ​ 24,643 5 - 39 1923 2010 ​ 909 Davis, Evanston, IL — ​ 4,912 ​ 18,229 ​ 8,112 ​ 4,912 ​ 26,341 ​ 31,253 ​ 6,985 ​ 24,268 5 - 39 2002 2011 ​ Legacy Tennyson Center, Plano, TX — ​ 3,067 ​ 22,064 ​ 3,411 ​ 3,067 ​ 25,475 ​ 28,542 ​ 6,390 ​ 22,152 5 - 39 2008 2011 ​ One Legacy Circle, Plano, TX — ​ 2,590 ​ 36,608 ​ 3,783 ​ 2,590 ​ 40,391 ​ 42,981 ​ 10,600 ​ 32,381 5 - 39 2008 2011 ​ One Ravinia Drive, Atlanta, GA — ​ 2,686 ​ 35,125 ​ 12,471 ​ 2,686 ​ 47,596 ​ 50,282 ​ 10,821 ​ 39,461 5 - 39 1985 2012 ​ Two Ravinia Drive, Atlanta, GA — ​ 7,375 ​ 58,726 ​ 12,259 ​ 7,375 ​ 70,985 ​ 78,360 ​ 11,630 ​ 66,730 5 - 39 1987 2015 ​ Westchase I & II, Houston, TX — ​ 8,491 ​ 121,508 ​ 14,548 ​ 8,491 ​ 136,056 ​ 144,547 ​ 29,975 ​ 114,572 5 - 39 2008 2012 ​ 1999 Broadway, Denver CO — ​ 16,334 ​ 137,726 ​ 38,338 ​ 16,334 ​ 176,064 ​ 192,398 ​ 34,199 ​ 158,199 5 - 39 1986 2013 ​ 999 Peachtree, Atlanta, GA — ​ 10,187 ​ 107,727 ​ 23,820 ​ 10,187 ​ 131,547 ​ 141,734 ​ 25,096 ​ 116,638 5 - 39 1987 2013 ​ 1001 17th Street, Denver, CO — ​ 17,413 ​ 165,058 ​ 22,284 ​ 17,413 ​ 187,342 ​ 204,755 ​ 35,495 ​ 169,260 5 - 39 2006 2013 ​ Plaza Seven, Minneapolis, MN ​ — ​ 6,604 ​ 54,240 ​ 11,073 ​ 6,604 ​ 65,313 ​ 71,917 ​ 9,175 ​ 62,742 5 - 39 1987 2016 ​ Pershing Plaza, Atlanta, GA ​ — ​ 5,300 ​ 34,158 ​ 2,040 ​ 5,300 ​ 36,198 ​ 41,498 ​ 4,110 ​ 37,388 5 - 39 1989 2016 ​ 600 17th Street, Denver, CO ​ — ​ 20,876 ​ 99,941 ​ 11,050 ​ 20,876 ​ 110,991 ​ 131,867 ​ 12,069 ​ 119,798 5 - 39 1982 2016 ​ Balance — Real Estate — ​ $ 189,649 ​ $ 1,556,258 ​ $ 394,826 ​ $ 189,155 ​ $ 1,951,578 ​ $ 2,140,733 ​ $ 538,717 ​ $ 1,602,016 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (1) There are no encumbrances on the above properties. (2) The aggregate cost for Federal Income Tax purposes is $2,419,780 . (3) Original date of acquisition by Sponsored Entity. ​ ​ ​ The following table summarizes the changes in the Company’s real estate investments and accumulated depreciation: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, (in thousands) 2020 2019 2018 Real estate investments, at cost: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance, beginning of year ​ $ 2,127,907 ​ $ 2,058,352 ​ $ 2,008,823 ​ Improvements ​ 75,472 ​ 74,324 ​ 53,279 ​ Dispositions ​ (62,646) ​ (4,769) ​ (3,750) ​ Balance, end of year - Real Estate ​ $ 2,140,733 ​ $ 2,127,907 ​ $ 2,058,352 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Accumulated depreciation: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance, beginning of year ​ $ 490,697 ​ $ 432,579 ​ $ 376,131 ​ Depreciation ​ 67,001 ​ 62,887 ​ 60,198 ​ Dispositions ​ (18,981) ​ (4,769) ​ (3,750) ​ Balance, end of year - Accumulated Depreciation ​ $ 538,717 ​ $ 490,697 ​ $ 432,579 ​ ​

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Significant Accounting Policies
Basis of Presentation	Basis of Presentation ​ The accompanying consolidated financial statements include all of the accounts of the Company and its majority-owned subsidiaries. All significant intercompany accounts and transactions have been eliminated in consolidation.
Estimates and Assumptions	Estimates and Assumptions ​ The Company prepares its financial statements and related notes in conformity with generally accepted accounting principles in the United States of America (“GAAP”). These principles require management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Actual results could differ from those estimates. Significant estimates in the consolidated financial statements include the allowance for doubtful accounts, purchase price allocations, impairment considerations, useful lives of fixed assets and the valuation of derivatives.
Investments in non-consolidated REITs	​ Investments in non-consolidated REITs ​ As of December 31, 2020, the Company has a non-controlling common stock interest in two Sponsored REITs in which the Company no longer shares in economic benefit or risk. The Company had a non-controlling common stock interest in another Sponsored REIT and a non-controlling preferred stock interest in additional Sponsored REITs, each of which were liquidated during 2019 or 2018. The Company exercised influence over, but did not control these entities and investments were accounted for using the equity method. Under the equity method of accounting, the Company's cost basis was adjusted by its share of the Sponsored REITs' earnings or losses. ​ The equity investments in Sponsored REITS were reviewed for impairment each reporting period. The Company recorded impairment charges when events or circumstances indicated a decline in the fair value below the carrying value of the investment had occurred and such decline was other-than-temporary. ​ On December 27, 2007, the Company purchased 965.75 preferred shares (approximately 43.7%) of a Sponsored REIT, FSP 303 East Wacker Drive Corp. (“East Wacker”), for $82.8 million. The Company agreed to vote its shares in any matter presented to a vote by the stockholders of East Wacker in the same proportion as shares voted by other stockholders of East Wacker. The investment in East Wacker was accounted for under the equity method. On September 24, 2018, the property owned by East Wacker was sold and, thereafter, East Wacker declared and issued a liquidating distribution to its preferred shareholders. ​ On May 29, 2009, the Company purchased 175.5 preferred shares (approximately 27.0%) of a Sponsored REIT, FSP Grand Boulevard Corp. (“Grand Boulevard”), for $15.0 million. The Company agreed to vote its shares in any matter presented to a vote by the stockholders of Grand Boulevard in the same proportion as shares voted by other stockholders of Grand Boulevard. The investment in Grand Boulevard was accounted for under the equity method. On July 19, 2018, the property owned by Grand Boulevard was sold and, thereafter, Grand Boulevard declared and issued a liquidating distribution for its preferred shareholders.
Real Estate and Depreciation	Real Estate and Depreciation ​ Real estate assets are stated at cost less accumulated depreciation. ​ The Company allocates the value of real estate acquired among land, buildings and identified intangible assets or liabilities. Costs related to land, building and improvements are capitalized. Typical capital items include new roofs, site improvements, various exterior building improvements and major interior renovations. Costs incurred in connection with leasing (primarily tenant improvements and leasing commissions) are capitalized and amortized over the lease period. Routine replacements and ordinary maintenance and repairs that do not extend the life of the asset are expensed as incurred. Depreciation is computed using the straight-line method over the assets’ estimated useful lives as follows: ​ ​ ​ ​ ​ ​ ​ Category Years Commercial buildings ​ 39 ​ ​ Building improvements 15 - 39 ​ Fixtures and equipment 3 - 7 ​ ​ The Company reviews its properties to determine if their carrying amounts will be recovered from future operating cash flows if certain indicators of impairment are identified at those properties. These indicators may include declining tenant occupancy, weak or declining tenant profitability, cash flows or liquidity, the Company’s decision to dispose of an asset before the end of its estimated useful life or legislative, economic, or market changes that permanently reduce the value of the Company’s investment. If indicators of impairment are present, the Company evaluates the carrying value of the property by comparing it to its expected future undiscounted cash flow. If the Company determines that impairment has occurred, the affected assets are reduced to their fair value. The evaluation of anticipated cash flows is highly subjective and is based in part on assumptions regarding future occupancy, rental rates and capital requirements that could differ materially from actual results in future periods. Since cash flows are considered on an undiscounted basis in the analysis that the Company conducts to determine whether an asset has been impaired, the Company’s strategy of holding properties over the long term directly decreases the likelihood of recording an impairment loss. If the Company’s strategy changes or market conditions otherwise dictate an earlier sale date, an impairment loss may be recognized. The Company did not recognize any impairment losses for the years ended December 31, 2020, 2019 or 2018.
Acquired Real Estate Leases and Amortization	Acquired Real Estate Leases and Amortization ​ Acquired real estate leases represent costs associated with acquiring an in-place lease (i.e., the market cost to execute a similar lease, including leasing commission, tenant improvements, legal, vacancy and other related costs) and the value relating to leases with rents above the market rate. Amortization is computed using the straight-line method over the term of the leases, which range from 47 months to 176 months . Amortization of these combined components was approximately $12.5 million, $18.9 million and $26.9 million for the years ended December 31, 2020, 2019 and 2018, respectively. ​ ​ Amortization related to costs associated with acquiring an in-place lease is included in depreciation and amortization on the consolidated statements of income. Amortization related to leases with rents above the market rate is offset against the rental revenue in the consolidated statements of income. The estimated annual amortization expense for the five years and thereafter following December 31, 2020 is as follows: ​ ​ ​ ​ ​ ​ (in thousands) December 31, 2021 ​ $ 8,975 ​ 2022 ​ 5,400 ​ 2023 ​ 4,268 ​ 2024 ​ 3,550 ​ 2025 ​ 2,797 ​ 2026 and thereafter ​ 3,216 ​
Acquired Unfavorable Real Estate Leases and Amortization	Acquired Unfavorable Real Estate Leases and Amortization ​ Acquired unfavorable real estate leases represent the value relating to leases with rents below the market rate. Amortization is computed using the straight-line method over the term of the leases, which range from 50 months to 176 months . Amortization expense was approximately $0.9 million, $1.3 million and $2.0 million for the years ended December 31, 2020, 2019 and 2018, respectively. ​ Amortization related to leases with rents below the market rate is included with rental revenue in the consolidated statements of income. The estimated annual amortization for the five years and thereafter following December 31, 2020 is as follows: ​ ​ ​ ​ ​ ​ (in thousands) December 31, 2021 ​ $ 597 ​ 2022 ​ 323 ​ 2023 ​ 218 ​ 2024 ​ 144 ​ 2025 ​ 92 ​ 2026 and thereafter ​ 218 ​
Assets held for sale	Asset Held For Sale ​ Classification of a property as held for sale typically occurs upon the execution of a purchase and sale agreement and belief by management that the sale or disposition is probable of occurrence within one year . Upon determining that a property was held for sale, the Company discontinues depreciating the property and reflects the property in its consolidated balance sheet at the lower of its carrying amount or fair value less the cost to sell. The Company presents the property held for sale on its consolidated balance sheet as “Asset held for sale”. The Company reports the results of operations of its properties sold or held for sale in its consolidated statements of income through the date of sale.
Cash and Cash Equivalents	Cash and Cash Equivalents ​ The Company considers all highly liquid instruments purchased with an original maturity of three months or less to be cash equivalents. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the consolidated balance sheets that sum to the total of the same such amounts shown in the consolidated statement of cash flows. ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, December 31, (in thousands) ​ 2020 ​ 2019 Cash and cash equivalents ​ $ 2,650 ​ $ 9,790 Restricted cash ​ 1,500 ​ — Total cash, cash equivalents and restricted cash ​ $ 4,150 ​ $ 9,790
Cash, Cash Equivalents and Restricted Cash	Restricted Cash ​ Restricted cash consists of tenant security deposits, which are required by law in some states or by contractual agreement to be kept in a segregated account, and escrows arising from property sales. Tenant security deposits are refunded when tenants vacate, provided that the tenant has not damaged the property. ​ Cash held in escrow is paid when the related issue is resolved. Restricted cash also may include funds segregated for specific tenant improvements per lease agreements.
Tenant Rent Receivables	Tenant Rent Receivables ​ Tenant rent receivables are expected to be collected within one year . The Company provided an allowance for doubtful accounts based on collectability. Lessors recognize the effect of a change in their assessment of whether the collectability of operating lease receivables are probable as an adjustment to lease income rather than bad debt expense.
Related Party Mortgage Loan Receivable	Related Party Mortgage Loan Receivable ​ Management monitors and evaluates the secured loans compared to the expected performance, cash flow and value of the underlying real estate and has not experienced a loss on these loans to date.
Concentration of Credit Risks	Concentration of Credit Risks ​ Financial instruments that potentially subject the Company to concentrations of credit risk consist primarily of cash investments, derivatives, related party mortgage loan receivable and accounts receivable. The Company maintains its cash balances principally in banks which the Company believes to be creditworthy. The Company periodically assesses the financial condition of the banks and believes that the risk of loss is minimal. Cash balances held with various financial institutions frequently exceed the insurance limit of provided by the Federal Deposit Insurance Corporation. The derivatives that the Company has are from interest rate swap agreements that are discussed in Note 5. The related party mortgage loan receivable is held with one Sponsored REIT. The Company performs regular evaluations on the extent and impact of any credit deterioration that could affect the performance and value of the secured property, as well as the financial and operating capability of the borrower. The Company performs ongoing credit evaluations of its tenants and requires certain tenants to provide security deposits or letters of credit. Though these security deposits and letters of credit are insufficient to meet the total value of a tenant’s lease obligation, they are a measure of good faith and a source of funds to offset the economic costs associated with lost rent and the costs associated with re-tenanting the space. The Company has no single tenant which accounts for more than
Financial Instruments	Financial Instruments ​ The Company estimates that the carrying values of cash and cash equivalents, restricted cash, receivables, prepaid expenses, accounts payable and accrued expenses, accrued compensation, and tenant security deposits approximate their fair values based on their short-term maturity and the bank note and term loans payable approximate their fair values as they bear interest at variable interest rates.
Straight-line Rent Receivable	Straight-line Rent Receivable ​ Certain leases provide for fixed rent increases over the term of the lease. Rental revenue is recognized on a straight-line basis over the related lease term; however, billings by the Company are based on the lease agreements. Straight-line rent receivable, which is the cumulative revenue recognized in excess of amounts billed by the Company, was 31, 2020 and 2019, respectively. Prior to 2020, the Company provided an allowance for doubtful accounts based on collectability. Lessors recognized the effect of a change in their assessment of whether the collectability of operating lease receivables are probable as an adjustment to lease income rather than bad debt expense. The reserve was eliminated during 2020 and no changes occurred during 2019 or 2018 based on such assessment.
Deferred Leasing Commissions	Deferred Leasing Commissions ​ Deferred leasing commissions represent direct and incremental external leasing costs incurred in the leasing of commercial space. These costs are capitalized and are amortized on a straight-line basis over the terms of the related lease agreements. Amortization expense was approximately ​ The estimated annual amortization for the five years and thereafter following December 31, 2020 is as follows: ​ ​ ​ ​ ​ ​ (in thousands) December 31, 2021 $ 9,957 ​ 2022 9,167 ​ 2023 8,041 ​ 2024 6,797 ​ 2025 5,621 ​ 2026 and thereafter 16,869 ​
Common Share Repurchases	Common Share Repurchases ​ The Company recognizes the gross cost of the common shares it repurchases as a reduction in stockholders’ equity using the treasury stock method. Maryland law does not recognize a separate treasury stock account but provides that shares repurchased are classified as authorized but unissued shares. Accordingly, the Company reduces common stock for the par value and the excess of the purchase price over the par value is a reduction to additional paid-in capital.
Revenue Recognition	Revenue Recognition ​ Rental Revenue - The Company has retained substantially all of the risks and benefits of ownership of the Company’s commercial properties and accounts for its leases as operating leases. Rental revenue includes income from leases, certain reimbursable expenses, straight-line rent adjustments and other income associated with renting the property. Rental income from leases, which includes rent concessions (including free rent and other lease inducements) and scheduled increases in rental rates during the lease term, is recognized on a straight-line basis. The Company does not have any significant percentage rent arrangements with its commercial property tenants. Reimbursable expenses are included in rental income in the period earned. A summary of rental revenue is shown in the following table: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, (in thousands) 2020 2019 2018 Income from leases ​ $ 180,899 ​ $ 191,828 ​ $ 202,127 ​ Reimbursable expenses ​ 61,310 ​ 64,421 ​ 61,475 ​ Straight-line rent adjustment ​ 1,685 ​ 8,876 ​ (381) ​ Amortization of favorable and unfavorable leases ​ 313 ​ 402 ​ 556 ​ ​ ​ $ 244,207 ​ $ 265,527 ​ $ 263,777 ​
Rental Revenue	Rental Revenue - The Company has retained substantially all of the risks and benefits of ownership of the Company’s commercial properties and accounts for its leases as operating leases. Rental revenue includes income from leases, certain reimbursable expenses, straight-line rent adjustments and other income associated with renting the property. Rental income from leases, which includes rent concessions (including free rent and other lease inducements) and scheduled increases in rental rates during the lease term, is recognized on a straight-line basis. The Company does not have any significant percentage rent arrangements with its commercial property tenants. Reimbursable expenses are included in rental income in the period earned. A summary of rental revenue is shown in the following table: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, (in thousands) 2020 2019 2018 Income from leases ​ $ 180,899 ​ $ 191,828 ​ $ 202,127 ​ Reimbursable expenses ​ 61,310 ​ 64,421 ​ 61,475 ​ Straight-line rent adjustment ​ 1,685 ​ 8,876 ​ (381) ​ Amortization of favorable and unfavorable leases ​ 313 ​ 402 ​ 556 ​ ​ ​ $ 244,207 ​ $ 265,527 ​ $ 263,777 ​
Related Party and Other Revenue	Related Party and Other Revenue -
Segment Reporting	Segment Reporting ​ The Company is a REIT focused on real estate investments primarily in the office market and currently operates in only one segment: real estate operations.
Income Taxes	Income Taxes ​ Taxes on income for the years ended December 31, 2020, 2019 and 2018 represent taxes incurred by FSP Protective TRS Corp, which is a taxable REIT subsidiary, and the State of Texas franchise tax applicable to FSP Corp., which is classified as an income tax for reporting purposes.
Net Income Per Share	Net Income Per Share ​ Basic net income per share is computed by dividing net income by the weighted average number of shares outstanding during the period. Diluted net income per share reflects the potential dilution that could occur if securities or other contracts to issue shares were exercised or converted into shares. There were
Derivative Instruments	Derivative Instruments ​ The Company recognizes derivatives on the consolidated balance sheets at fair value. Derivatives that do not qualify, or are not designated as hedge relationships, must be adjusted to fair value through income. Derivative instruments designated in a hedge relationship to mitigate exposure to variability in expected future cash flows, or other types of forecasted transactions, are considered cash flow hedges. Cash flow hedges are accounted for by recording the fair value of the derivative instrument on the consolidated balance sheets as either an asset or liability. To the extent hedges are effective, a corresponding amount, adjusted for swap payments, is recorded in accumulated other comprehensive income within stockholders’ equity. Amounts are then reclassified from accumulated other comprehensive income to the income statement in the period or periods the hedged forecasted transaction affects earnings. Ineffectiveness, if any, is recognized in other comprehensive income (“OCI”) and reclassified into the income statement. The Company reviews the effectiveness of each hedging transaction, which involves estimating future cash flows, at least quarterly. Derivative instruments designated in a hedge relationship to mitigate exposure to changes in the fair value of an asset, liability, or firm commitment attributable to a particular risk, such as interest rate risk, are considered fair value hedges. The Company currently has
Fair Value Measurements	Fair Value Measurements ​ Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. There is also an established fair value hierarchy which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The standard describes three levels of inputs that may be used to measure fair value. Financial assets and liabilities recorded on the consolidated balance sheets at fair value are categorized based on the inputs to the valuation techniques as follows: ​ Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access. Level 2 inputs are inputs other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. Level 2 inputs may include quoted prices for similar assets and liabilities in active markets, as well as inputs that are observable for the asset or liability (other than quoted prices), such as interest rates and yield curves that are observable at commonly quoted intervals. Level 3 inputs are unobservable inputs for the asset or liability, which is typically based on an entity’s own assumptions, as there is little, if any, related market activity or information. In instances where the determination of the fair value measurement is based on inputs from different levels of the fair value hierarchy, the level in the fair value hierarchy within which the entire fair value measurement falls is based on the lowest level input that is significant to the fair value measurement in its entirety. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment, and considers factors specific to the asset or liability including credit risk, which was not significant to the overall value. These inputs (See Notes 3 and 5) were considered and applied to the Company’s derivative instruments and Sponsored REIT Loan. Level 2 inputs were used to value the interest rate swaps and Level 3 inputs were used to value the Sponsored REIT Loan.
Subsequent Events	Subsequent Events ​ In preparing these consolidated financial statements the Company evaluated events that occurred through the date of issuance of these financial statements for potential recognition or disclosure.
Recent Accounting Standards	Recent Accounting Standards ​ In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13” or “CECL”), which requires that entities use a new forward looking “expected loss” model that generally will result in the earlier recognition of allowance for credit losses. The measurement of expected credit losses is based upon historical experience, current conditions, and reasonable and supportable forecasts that affect the collectability of the reported amount. ASU 2016-13 is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. The Company’s Sponsored REIT Loan (as defined in Note 3 below) receivables are within the scope of this standard and the Company’s analysis was completed using a Probability of Default / Loss Given Default Model. The Company’s receivables associated with its real estate operating leases are not within the scope of this standard. The Company adopted this standard on January 1, 2020. The adoption of this standard did not have a material impact on the Company’s consolidated financial statements. ​ In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”). The ASU is intended to improve the effectiveness of fair value measurement disclosures. ASU 2018-13 is effective for all entities for annual periods beginning after December 15, 2019, and interim periods within those fiscal years. This ASU amends existing fair value measurement disclosure requirements by adding, changing, or removing certain disclosures. The Company adopted this standard on January 1, 2020. The adoption of this standard did not have a material impact on the Company’s consolidated financial statements. ​ In April 2019, the FASB issued ASU No. 2019-04, Codification Improvements to Topics 326, Financial Instruments - Credit Losses, Topic 815 Derivatives and Hedging and Topic 825, Financial Instruments (“ASU 2019-04”). The ASU clarifies areas of guidance related to the recently issued standards on credit losses (Topic 326), derivatives and hedging (Topic 815), and recognition and measurement of financial instruments (Topic 825). ASU 2019-04 is effective for fiscal years beginning after December 15, 2019. The Company adopted this standard on January 1, 2020. The adoption of this standard did not have a material impact on the Company’s consolidated financial statements. ​ In March 2020, the FASB issued ASU No. 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting (“ASU 2020-04”). The ASU contains practical expedients for reference rate reform related activities that impact debt, leases, derivatives and other contracts. The guidance in ASU 2020-04 is optional and may be elected over time as reference rate reform activities occur. The Company is currently assessing the potential impact that the adoption of ASU 2020-04 may have on its consolidated financial statements.

Significant Accounting Polici_3

Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2020
Significant Accounting Policies
Schedule of estimated useful lives of real estate assets	​ ​ ​ ​ ​ ​ ​ Category Years Commercial buildings ​ 39 ​ ​ Building improvements 15 - 39 ​ Fixtures and equipment 3 - 7 ​
Schedule of estimated annual amortization expense for succeeding five years for acquired in-place lease and above-market leases	​ ​ ​ ​ ​ ​ (in thousands) December 31, 2021 ​ $ 8,975 ​ 2022 ​ 5,400 ​ 2023 ​ 4,268 ​ 2024 ​ 3,550 ​ 2025 ​ 2,797 ​ 2026 and thereafter ​ 3,216 ​
Schedule of estimated annual amortization for unfavorable leases	​ ​ ​ ​ ​ ​ (in thousands) December 31, 2021 ​ $ 597 ​ 2022 ​ 323 ​ 2023 ​ 218 ​ 2024 ​ 144 ​ 2025 ​ 92 ​ 2026 and thereafter ​ 218 ​
Schedule of Cash and cash equivalents	​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, December 31, (in thousands) ​ 2020 ​ 2019 Cash and cash equivalents ​ $ 2,650 ​ $ 9,790 Restricted cash ​ 1,500 ​ — Total cash, cash equivalents and restricted cash ​ $ 4,150 ​ $ 9,790
Schedule of estimated annual amortization for deferred leasing commissions	​ ​ ​ ​ ​ ​ (in thousands) December 31, 2021 $ 9,957 ​ 2022 9,167 ​ 2023 8,041 ​ 2024 6,797 ​ 2025 5,621 ​ 2026 and thereafter 16,869 ​
Summary of rental revenue	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, (in thousands) 2020 2019 2018 Income from leases ​ $ 180,899 ​ $ 191,828 ​ $ 202,127 ​ Reimbursable expenses ​ 61,310 ​ 64,421 ​ 61,475 ​ Straight-line rent adjustment ​ 1,685 ​ 8,876 ​ (381) ​ Amortization of favorable and unfavorable leases ​ 313 ​ 402 ​ 556 ​ ​ ​ $ 244,207 ​ $ 265,527 ​ $ 263,777 ​

Related Party Transactions an_2

Related Party Transactions and Investments in Non-Consolidated Entities (Tables)	12 Months Ended
	Dec. 31, 2020
Related Party Transactions and Investments in Non-Consolidated Entities
Schedule of equity in losses of investments in non-consolidated REITs	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ ​ ​ December 31, ​ (in thousands) 2018 ​ ​ ​ ​ Equity in income of East Wacker ​ $ 7,209 ​ Equity in loss of Grand Boulevard ​ ​ (107) ​ Impairment charge ​ (309) ​ Total ​ $ 6,793 ​
Schedule of distributions received from non-consolidated REITs	​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ ​ ​ December 31, ​ (in thousands) 2018 ​ ​ ​ ​ ​ Distributions from East Wacker ​ $ 657 ​ Distributions from Grand Boulevard ​ 53 ​ ​ ​ $ 710 ​
Summary of financial information of Sponsored REITs	​ ​ ​ ​ ​ ​ ​ December 31, (in thousands) ​ 2018 ​ ​ ​ ​ Balance Sheet Data (unaudited): ​ ​ ​ ​ Real estate, net ​ $ 97,034 ​ Other assets ​ 18,532 ​ Total liabilities ​ (75,382) ​ Shareholders’ equity ​ $ 40,184 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ ​ ​ December 31, ​ (in thousands) 2018 ​ ​ ​ ​ Operating Data (unaudited): ​ ​ ​ ​ Rental revenues ​ $ 40,382 ​ Other revenues ​ 1 ​ Operating and maintenance expenses ​ (20,584) ​ Depreciation and amortization ​ (13,077) ​ Interest expense ​ (6,869) ​ Gain on sale ​ 17,095 ​ Net income ​ $ 16,948 ​
Summary of the Sponsored REIT Loans outstanding	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Maximum Amount Interest (dollars in thousands, except footnotes) ​ ​ Maturity ​ Amount ​ Outstanding Rate at Sponsored REIT Location ​ Date ​ of Loan ​ 31-Dec-20 31-Dec-20 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Mortgage loan secured by property ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ FSP Monument Circle LLC (1) ​ Indianapolis, IN ​ 6-Dec-22 ​ $ 21,000 ​ $ 21,000 7.51 % ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 21,000 ​ $ 21,000 ​ ​ (1) This mortgage loan includes an origination fee of $164,000 and an exit fee of $38,000 when repaid by the borrower.

Bank Note Payable, Term Note Pa

Bank Note Payable, Term Note Payable and Private Placements (Tables)	12 Months Ended
	Dec. 31, 2020
BAML Revolver
Debt Instrument [Line Items]
Schedule of actual amount of applicable facility fee, LIBOR rate or base rate determined based on total leverage ratio	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Base ​ ​ ​ ​ ​ LIBOR Rate ​ Facility ​ Rate ​ Level Credit Rating Margin Fee Margin I A- / A3 (or higher) 0.825 % 0.125 % 0.000 % II BBB+ / Baa1 ​ 0.875 % 0.150 % 0.000 % III BBB / Baa2 ​ 1.000 % 0.200 % 0.000 % IV BBB- / Baa3 ​ 1.200 % 0.250 % 0.200 % V <BBB- / Baa3 ​ 1.550 % 0.300 % 0.550 %
BAML Term Loan
Debt Instrument [Line Items]
Schedule of actual amount of applicable facility fee, LIBOR rate or base rate determined based on total leverage ratio	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ LIBOR Rate ​ Base Rate ​ Level Credit Rating Margin Margin I A- / A3 (or higher) 0.900 % 0.000 % II BBB+ / Baa1 ​ 0.950 % 0.000 % III BBB / Baa2 ​ 1.100 % 0.100 % IV BBB- / Baa3 ​ 1.350 % 0.350 % V <BBB- / Baa3 ​ 1.750 % 0.750 %
JPM Term Loan
Debt Instrument [Line Items]
Schedule of actual amount of applicable facility fee, LIBOR rate or base rate determined based on total leverage ratio	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ LIBOR-BASED ​ ​ ​ CREDIT ​ RATE ​ BASE RATE LEVEL ​ RATING ​ MARGIN ​ MARGIN I A- / A3 (or higher) 85.0 bps — bps II ​ BBB+ / Baa1 ​ 90.0 bps — bps III ​ BBB / Baa2 ​ 100.0 bps — bps IV ​ BBB- / Baa3 ​ 125.0 bps 25.0 bps V ​ <BBB- / Baa3 ​ 165.0 bps 65.0 bps
BMO Term Loan
Debt Instrument [Line Items]
Schedule of actual amount of applicable facility fee, LIBOR rate or base rate determined based on total leverage ratio	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Credit ​ LIBOR Rate ​ Base Rate ​ Level Rating Margin Margin I ​ A- / A3 (or higher) ​ 85.0 bps — bps II ​ BBB+ / Baa1 ​ ​ 90.0 bps — bps III ​ BBB / Baa2 ​ ​ 100.0 bps — bps IV ​ BBB- / Baa3 ​ ​ 125.0 bps 25.0 bps V ​ <BBB- / Baa3 ​ ​ 165.0 bps 65.0 bps

Financial Instruments_ Deriva_2

Financial Instruments: Derivatives and Hedging (Tables)	12 Months Ended
	Dec. 31, 2020
Financial Instruments: Derivatives and Hedging
Schedule of notional and fair value of derivative financial instruments	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Notional Strike Effective Expiration Fair Value (2) at December 31, (in thousands) ​ Value ​ Rate ​ Date ​ Date ​ 2020 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2017 Interest Rate Swap ​ $ 400,000 1.12 % Sep-17 Sep-21 ​ $ (2,947) ​ $ 3,022 ​ 2019 JPM Interest Rate Swap ​ $ 100,000 2.44 % Mar-19 Nov-21 ​ $ (2,102) ​ $ (1,634) ​ 2019 BMO Interest Rate Swap (1) ​ $ 220,000 2.39 % Aug-20 Jan-24 ​ $ (12,262) ​ $ (5,107) ​ 2013 BMO Interest Rate Swap ​ $ 220,000 2.32 % Aug-13 Aug-20 ​ $ — ​ $ (963) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (1) The Notional Value will decrease to $165 million on November 30, 2021. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (2) Classified within Level 2 of the fair value hierarchy. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Summary of Interest Rate Swaps that was recorded in OCI	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ Year Ended December 31, Interest Rate Swaps in Cash Flow Hedging Relationships: 2020 2019 2018 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Amounts of gain (loss) recognized in OCI ​ $ (20,380) ​ $ (15,119) ​ $ 5,321 Amounts of previously recorded gain/(loss) reclassified from OCI into Interest Expense ​ $ (7,751) ​ $ 4,328 ​ $ 2,722 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total amount of Interest Expense presented in the consolidated statements of operations ​ $ 36,026 ​ $ 36,757 ​ $ 38,374

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2020
Stockholders' Equity
Schedule of Share-based Payment Arrangement, Nonemployee Director Award Plan, Activity	​ ​ ​ ​ ​ ​ ​ ​ ​ Shares Available ​ Compensation (in thousands) ​ for Grant ​ Cost ​ ​ ​ ​ ​ ​ ​ Balance, December 31, 2016, 2017 and 2018 ​ ​ 1,944,428 ​ ​ ​ Shares granted 2019 ​ ​ (38,046) ​ $ 337,000 Balance December 31, 2019 ​ ​ 1,906,382 ​ ​ 337,000 Shares granted 2020 ​ ​ (58,998) ​ ​ 337,000 Balance December 31, 2020 ​ ​ 1,847,384 ​ $ 674,000

Federal Income Tax Reporting (T

Federal Income Tax Reporting (Tables)	12 Months Ended
	Dec. 31, 2020
Federal Income Tax Reporting
Schedule of income tax expense reflected in the condensed consolidated statements of income	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Year Ended December 31, (Dollars in thousands) 2020 2019 2018 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revised Texas Franchise Tax ​ $ 250 ​ $ 394 ​ $ 319 ​ Other Taxes ​ — ​ (125) ​ 41 ​ Tax expense ​ $ 250 ​ $ 269 ​ $ 360 ​
Schedule of reconciliation of book net income to taxable income	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the year ended December 31, (in thousands) 2020 2019 2018 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income per GAAP ​ $ 32,615 ​ $ 6,475 ​ $ 13,069 ​ Adjustments to GAAP net income: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ GAAP depreciation and amortization ​ 88,244 ​ 90,507 ​ 93,675 ​ Tax depreciation and amortization ​ (79,542) ​ (66,376) ​ (62,657) ​ Tax basis more than GAAP basis on assets sold ​ (11,450) ​ — ​ — ​ Straight line rent adjustment, net ​ (1,685) ​ (10,462) ​ (1,350) ​ Deferred rent, net ​ 1,956 ​ 535 ​ 210 ​ Non-taxable distributions ​ — ​ — ​ (710) ​ Other, net ​ 390 ​ 4,099 ​ (6,651) ​ Taxable income ​ 30,528 ​ 24,778 ​ 35,586 ​ Less: Capital gains recognized ​ 7,576 ​ — ​ — ​ Taxable income subject to distribution requirement ​ $ 22,952 ​ $ 24,778 ​ $ 35,586 ​
Summary of tax components of Company's common distribution paid per share	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ 2019 ​ 2018 ​ Per Share % Per Share % Per Share % Ordinary income (1) ​ $ 0.28 77.51 % $ 0.25 69.96 % $ 0.35 76.39 % Capital gain ​ 0.06 16.72 % — — % — — % Return of capital ​ 0.02 5.77 % 0.11 30.04 % 0.11 23.61 % Total ​ $ 0.36 100 % $ 0.36 100 % $ 0.46 100 %

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2020
Leases
Summary of lease costs and maturity analysis for liabilities	​ ​ ​ ​ ​ ​ ​ Lease Costs ​ ​ ​ ​ ​ Year Ended (in thousands) ​ December 31, 2020 ​ December 31, 2019 Operating lease cost $ 419 ​ $ 419 ​ $ 419 ​ $ 419 ​ ​ ​ ​ ​ ​ Other information ​ ​ ​ ​ ​ Cash paid for amounts included in the measurement of lease liabilities ​ 421 ​ ​ 412 Weighted average remaining lease terms in years - operating leases ​ 3.75 ​ ​ 4.75 Weighted average discount rate - operating leases ​ 3.86% ​ ​ 3.86% ​ ​ ​ ​ ​ ​ Maturity analysis for liabilities Total ​ ​ ​ Undiscounted ​ ​ ​ (in thousands) Cash Flows ​ ​ ​ Discount rate at commencement ​ 3.86% ​ ​ ​ 2021 $ 429 ​ ​ ​ 2022 ​ 438 ​ ​ ​ 2023 ​ 447 ​ ​ ​ 2024 ​ 340 ​ ​ ​ ​ $ 1,654 ​ ​ ​ ​ ​ ​ ​ ​ ​ Present value lease liability $ 1,536 ​ ​ ​ ​ ​ ​ ​ ​ ​ Difference between undiscounted cash flows and discounted cash flows $ 118 ​ ​ ​
Summary of income relating to lease payments and undiscounted cash flows	​ ​ ​ ​ ​ ​ ​ ​ Income relating to lease payments: ​ ​ ​ ​ Year Ended (in thousands) December 31, 2020 December 31, 2019 Income from leases (1) ​ $ 242,209 ​ $ 256,250 ​ ​ $ 242,209 ​ $ 256,250 ​ ​ ​ ​ ​ ​ ​ Undiscounted Cash Flows Year ending ​ ​ ​ (in thousands) ​ December 31, ​ ​ ​ 2021 ​ ​ 162,676 ​ ​ ​ 2022 ​ ​ 146,031 ​ ​ ​ 2023 ​ ​ 138,363 ​ ​ ​ 2024 ​ ​ 127,269 ​ ​ ​ 2025 ​ ​ 107,596 ​ ​ ​ 2026 and thereafter ​ 361,423 ​ ​ ​ ​ ​ $ 1,043,358 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (1) Amounts recognized from variable lease payments were variable lease payments $61,310 and $64,421 for the years ended December 31, 2020 and 2019, respectively. ​ ​ ​ ​ ​ ​

Selected Unaudited Quarterly _2

Selected Unaudited Quarterly Information (Tables)	12 Months Ended
	Dec. 31, 2020
Selected Unaudited Quarterly Information
Schedule of selected unaudited quarterly information	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ First Second Third Fourth ​ ​ Quarter ​ Quarter ​ Quarter ​ Quarter ​ ​ (in thousands, except per share data) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenue ​ $ 62,983 ​ $ 60,808 ​ $ 62,247 ​ $ 59,810 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) ​ $ (1,071) ​ $ (2,075) ​ $ (1,679) ​ $ 37,440 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basic and diluted net income (loss) per share ​ $ (0.01) ​ $ (0.02) ​ $ (0.02) ​ $ 0.35 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average number of shares outstanding ​ 107,269 ​ 107,287 ​ 107,328 ​ 107,328 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 ​ First Second Third Fourth ​ ​ Quarter ​ Quarter ​ Quarter ​ Quarter ​ ​ (in thousands, except per share data) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenue ​ $ 64,716 ​ $ 66,813 ​ $ 68,539 ​ $ 68,997 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) ​ $ (1,205) ​ $ 1,633 ​ $ 2,399 ​ $ 3,648 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basic and diluted net income (loss) per share ​ $ (0.01) ​ $ 0.02 ​ $ 0.02 ​ $ 0.03 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average number of shares outstanding ​ 107,231 ​ 107,231 ​ 107,231 ​ 107,240 ​

Organization (Details)

Organization (Details)	12 Months Ended
	Dec. 31, 2020propertyentity	Dec. 31, 2019entity	Dec. 31, 2018entity
Organization
Number of REITs in which the entity holds non-controlling common stock interest	2	2	3
Number of Sponsored REITs	2		3
Number of properties in redevelopment | property	2
Number of promissory notes secured by mortgages on real estate owned by Sponsored REITs	1
Properties
Number of properties | property	32
FSP Investments LLC
Organization
Ownership interest (as a percent)	100.00%
FSP Property Management LLC
Organization
Ownership interest (as a percent)	100.00%
FSP Holdings LLC
Organization
Ownership interest (as a percent)	100.00%
FSP Protective TRS Corp.
Organization
Ownership interest (as a percent)	100.00%

Significant Accounting Polici_4

Significant Accounting Policies - Basis, Estimates and Inv in non-consolidated REITs (Detail) - entity	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Significant Accounting Policies
Number of corporations organized to operate as real estate investment trusts (REITs)	2	2	3
Number of REITs in which the entity holds non-controlling preferred stock interest	2	2

Significant Accounting Polici_5

Significant Accounting Policies - Inv in non-consolidated REITs (Details) - USD ($) $ in Millions	May 29, 2009	Dec. 27, 2007	May 31, 2009	Dec. 31, 2007
East Wacker
Investment in Sponsored REITs
Preferred shares purchased		965.75		965.75
Percentage of outstanding preferred shares purchased		43.70%		43.70%
Net cost of preferred shares purchased		$ 82.8
Grand Boulevard
Investment in Sponsored REITs
Preferred shares purchased	175.5		175.5
Percentage of outstanding preferred shares purchased	27.00%		27.00%
Net cost of preferred shares purchased	$ 15

Significant Accounting Polici_6

Significant Accounting Policies - Estimated Useful Lives (Details)	12 Months Ended
	Dec. 31, 2020
Commercial buildings
Real Estate and Depreciation
Estimated useful life	39 years
Building improvements | Minimum
Real Estate and Depreciation
Estimated useful life	15 years
Building improvements | Maximum
Real Estate and Depreciation
Estimated useful life	39 years
Fixtures and equipment | Minimum
Real Estate and Depreciation
Estimated useful life	3 years
Fixtures and equipment | Maximum
Real Estate and Depreciation
Estimated useful life	7 years

Significant Accounting Polici_7

Significant Accounting Policies - Acquired Real Estate Leases and Amortization (Details) - Acquired in-place and above market real estate leases - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Acquired real estate leases and amortization
Amortization expense	$ 12,500	$ 18,900	$ 26,900
Estimated annual amortization for succeeding five years
2021	8,975
2022	5,400
2023	4,268
2024	3,550
2025	2,797
2026 and thereafter	$ 3,216
Minimum
Acquired real estate leases and amortization
Term of lease	47 months
Maximum
Acquired real estate leases and amortization
Term of lease	176 months

Significant Accounting Polici_8

Significant Accounting Policies - Acquired Unfavorable Real Estate Leases and Amortization (Details) - Acquired unfavorable real estate leases - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Acquired Unfavorable Real Estate Leases and Amortization
Amortization	$ 900	$ 1,300	$ 2,000
Estimated annual amortization for succeeding five years
2021	597
2022	323
2023	218
2024	144
2025	92
2026 and thereafter	$ 218
Minimum
Acquired Unfavorable Real Estate Leases and Amortization
Term of lease	50 months
Maximum
Acquired Unfavorable Real Estate Leases and Amortization
Term of lease	176 months

Significant Accounting Polici_9

Significant Accounting Policies - Asset Held For Sale, Cash (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Discontinued Operations
Time period within which sale or disposition of properties held for sale is probable	1 year
Cash, Cash Equivalents and Restricted Cash
Cash and cash equivalents	$ 2,650	$ 9,790
Restricted cash	1,500
Total cash, cash equivalents and restricted cash	$ 4,150	$ 9,790	$ 11,177	$ 9,819

Significant Accounting Polic_10

Significant Accounting Policies - Rent Receivables (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Tenant Rent Receivables and Straight-line Rent Receivable
Period within which tenant rent receivables are expected to be collected	1 year
Straight-line rent receivable	$ 67.8	$ 66.9

Significant Accounting Polic_11

Significant Accounting Policies - Concentration of Credit Risks (Details)	12 Months Ended
	Dec. 31, 2020USD ($)item
Concentration of Credit Risks
Number of banks in which the entity maintains cash balances	2
Number of interest rate swap agreements	3
Cash balances with financial institutions | Credit concentration risk | Minimum
Concentration of Credit Risks
Insurance limit provided by Federal Deposit Insurance Corporation | $	$ 250,000
Annualized rental revenues | Single tenant rental revenues
Concentration of Credit Risks
Percentage of annualized rental revenues required for qualification as major tenant	10.00%

Significant Accounting Polic_12

Significant Accounting Policies - Deferred Leasing Commissions and Revenue Recognition (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020USD ($)shares	Sep. 30, 2020shares	Jun. 30, 2020shares	Mar. 31, 2020shares	Dec. 31, 2019shares	Sep. 30, 2019shares	Jun. 30, 2019shares	Mar. 31, 2019shares	Dec. 31, 2020USD ($)itemshares	Dec. 31, 2019USD ($)shares	Dec. 31, 2018USD ($)shares
Deferred Leasing Commissions
Amortization of deferred leasing commissions											$ 8,500
Amortization of deferred leasing commissions									$ 9,600	$ 9,900
Estimated annual amortization of deferred leasing commissions for the succeeding five years
2021									9,957
2022									9,167
2023									8,041
2024									6,797
2025									5,621
2026 and thereafter									16,869
Summary of rental revenue
Income from leases									180,899	191,828	202,127
Reimbursable expenses									61,310	64,421	61,475
Straight Line Rent Adjustments									1,685	8,876	(381)
Amortization of favorable and unfavorable leases									313	402	556
Total											$ 263,777
Total									$ 244,207	$ 265,527
Segment Reporting
Number of reporting segments | item									1
Net Income Per Share
Potential dilutive shares outstanding | shares									0	0	0
Denominator used for calculating basic and diluted net income per share (in shares) | shares	107,328,000	107,328,000	107,287,000	107,269,000	107,240,000	107,231,000	107,231,000	107,231,000	107,303,000	107,233,000	107,231,000
Derivative instruments
Fair value hedges outstanding	$ 0								$ 0
Rental
Summary of rental revenue
Total											$ 263,777
Total									$ 244,207	$ 265,527

Related Party Transactions an_3

Related Party Transactions and Investments in Non-Consolidated Entities - Investment in Sponsored REITs (Details) - entity	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Related Party Transactions and Investments in Non-Consolidated Entities
Number of REITs in which the entity holds non-controlling common stock interest	2	2	3
Number of REITs in which the entity holds non-controlling preferred stock interest	2	2

Related Party Transactions an_4

Related Party Transactions and Investments in Non-Consolidated Entities - Investment in Sponsored REITs - Property Sold (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)
FSP Energy Tower I Corp.
Investment in Sponsored REITs
Repayment of principal	$ 51

Related Party Transactions an_5

Related Party Transactions and Investments in Non-Consolidated Entities - Equity in losses of investment in non-consolidated REITs (Details) - USD ($) $ in Thousands

Apr. 03, 2019

Feb. 02, 2019

Sep. 27, 2018

Sep. 24, 2018

Aug. 17, 2018

Jul. 19, 2018

May 29, 2009

Dec. 27, 2007

Jun. 30, 2018

May 31, 2009

Dec. 31, 2007

Dec. 31, 2019

Dec. 31, 2018

Sponsored REITs

Equity in income (loss)

$ 6,793

Impairment charge

$ (300)

(309)

Proceeds received from liquidating trust

$ 1,470

Amount received

74,931

Distributions received from non-consolidated REITs

Distributions from non-consolidated REITs

710

East Wacker

Sponsored REITs

Equity in income (loss)

7,209

Preferred shares purchased

965.75

965.75

Percentage of outstanding preferred shares purchased

43.70%

43.70%

Liquidating distribution receivable

$ 70,000

Gain (loss) on liquidation

$ 7,100

Proceeds received from liquidating trust

$ 1,000

Amount received

$ 69,000

Distributions received from non-consolidated REITs

Distributions from non-consolidated REITs

657

Grand Boulevard

Sponsored REITs

Equity in income (loss)

(107)

Preferred shares purchased

175.5

175.5

Percentage of outstanding preferred shares purchased

27.00%

27.00%

Liquidating distribution receivable

$ 6,200

Gain (loss) on liquidation

$ (100)

Proceeds received from liquidating trust

$ 200

Amount received

$ 5,900

Beneficial interest

$ 100

Distributions received from non-consolidated REITs

Distributions from non-consolidated REITs

$ 53

Related Party Transactions an_6

Related Party Transactions and Investments in Non-Consolidated Entities - Summarized financial information for Sponsored REITs (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020USD ($)entity	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2020USD ($)entity	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)entity	Dec. 31, 2017USD ($)
Schedule of Equity Method Investments [Line Items]
Number of Sponsored REITs the Company held an interest in at period end | entity	2								2		3
Number of REITs in which are included in the operations data | entity											6
Balance Sheet Data (unaudited):
Real Estate Investment Property, Net	$ 1,602,016				$ 1,637,210				$ 1,602,016	$ 1,637,210
Total liabilities	(1,025,093)				(1,056,258)				(1,025,093)	(1,056,258)
Total stockholders' equity	768,091				786,396				768,091	786,396	$ 837,634	$ 871,292
Operating Data (unaudited):
Rental revenues											263,777
Other revenues	59,810	$ 62,247	$ 60,808	$ 62,983	68,997	$ 68,539	$ 66,813	$ 64,716
Depreciation and amortization									(91,581)	(93,787)	(97,171)
Interest expense									(36,026)	(36,757)	(38,374)
Net income	$ 37,440	$ (1,679)	$ (2,075)	$ (1,071)	$ 3,648	$ 2,399	$ 1,633	$ (1,205)	32,615	6,475	13,069
Sponsored REITs
Balance Sheet Data (unaudited):
Real Estate Investment Property, Net											97,034
Other assets											18,532
Total liabilities											(75,382)
Total stockholders' equity											40,184
Operating Data (unaudited):
Rental revenues											40,382
Operating and maintenance expenses											(20,584)
Depreciation and amortization											(13,077)
Interest expense											(6,869)
Gain (Loss) on Sale of Properties, Net of Applicable Income Taxes											17,095
Net income											16,948
Related party revenue: Other
Operating Data (unaudited):
Other revenues									$ 31	$ 21	32
Related party revenue: Other | Sponsored REITs
Operating Data (unaudited):
Other revenues											$ 1

Related Party Transactions an_7

Related Party Transactions and Investments in Non-Consolidated Entities - Management fees and interest income from loans (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Asset management fees, low end of range (as a percent)									1.00%
Asset management fees, high end of range (as a percent)									5.00%
Notice period for cancellation of applicable contracts									30 days
Revenue	$ 59,810,000	$ 62,247,000	$ 60,808,000	$ 62,983,000	$ 68,997,000	$ 68,539,000	$ 66,813,000	$ 64,716,000
Revenue, Product and Service [Extensible List]									Asset management fees	Asset management fees	Asset management fees
Impairment of Sponsored REIT	$ 0								$ 0
Asset management fees
Schedule of Equity Method Investments [Line Items]
Revenue									$ 100,000	$ 200,000	$ 500,000

Related Party Transactions an_8

Related Party Transactions and Investments in Non-Consolidated Entities - Sponsored REIT Loans outstanding (Details) - USD ($)	Dec. 06, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 05, 2020
Sponsored REITs
Maximum amount of loan		$ 21,000,000
Amount Drawn		21,000,000	$ 21,000,000
Interest income and fees from the Sponsored REIT Loans		1,500,000	3,300,000	$ 4,600,000
Related party mortgage loan receivable		$ 21,000,000	$ 21,000,000
Sponsored REITs
Sponsored REITs
Term of sponsored REIT loan secured by mortgage, minimum		1 year
Term of sponsored REIT loan secured by mortgage, maximum		3 years
Mortgage loan secured by property | Sponsored REITs
Sponsored REITs
Interest rate (as a percent)	7.51%				7.19%
Mortgage Loan On Real Estate, Extended Term	2 years
Mortgage loan secured by property | Sponsored REITs | Fair Value, Inputs, Level 3 [Member]
Sponsored REITs
Amount Drawn		$ 20,400,000
Related party mortgage loan receivable		20,400,000
Mortgage loan secured by property | FSP Monument Circle LLC
Sponsored REITs
Maximum amount of loan		21,000,000
Amount Drawn		$ 21,000,000
Interest rate (as a percent)		7.51%
Origination fee		$ 164,000
Exit fee		38,000
Related party mortgage loan receivable		$ 21,000,000

Bank Note Payable, Term Loans_2

Bank Note Payable, Term Loans Payable and Senior Notes (Details)	Dec. 24, 2020USD ($)	Oct. 24, 2017USD ($)	Sep. 27, 2012USD ($)	Dec. 31, 2020USD ($)period	Dec. 23, 2020USD ($)	Dec. 31, 2019USD ($)	Aug. 02, 2018USD ($)
Debt Instrument [Line Items]
Repayments of Unsecured Debt				$ 50,000,000
Unsecured term loan				717,323,000		$ 765,733,000
Portion of future LIBOR-based rate risk				17,300,000
Borrowings outstanding				$ 3,500,000
Senior Notes
Debt Instrument [Line Items]
Principal amount of loan		$ 200,000,000
Fixed charge coverage ratio		1.50
Series A Notes
Debt Instrument [Line Items]
Principal amount of loan		$ 116,000,000
Interest rate (as a percent)		3.99%
Series B Notes
Debt Instrument [Line Items]
Principal amount of loan		$ 84,000,000
Interest rate (as a percent)		4.26%
Maximum | Senior Notes
Debt Instrument [Line Items]
Unsecured leverage ratio		60.00%
Unsecured leverage ratio for significant acquisition		65.00%
BAML Credit Facility | Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				0.50%
BAML Credit Facility | One month LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				1.00%
BAML Revolver
Debt Instrument [Line Items]
Weighted average interest rate (as a percent)				1.65%		3.67%
Effective interest rate (as a percent)				1.34%
Total available				$ 600,000,000
Number of periods of extension | period				2
Length of extension period				6 months
Additional borrowing capacity allowed by exercising an accordion feature				$ 500,000,000
Borrowings outstanding				$ 3,500,000		$ 0
Facility fee at period end (as a percent)				0.25%
BAML Revolver | A- | A3 | Minimum
Debt Instrument [Line Items]
Facility fee (as a percent)				0.125%
BAML Revolver | BBB+ | Baa1
Debt Instrument [Line Items]
Facility fee (as a percent)				0.15%
BAML Revolver | BBB | Baa2
Debt Instrument [Line Items]
Facility fee (as a percent)				0.20%
BAML Revolver | BBB- | Baa3
Debt Instrument [Line Items]
Facility fee (as a percent)				0.25%
BAML Revolver | BBB- | Baa3 | Maximum
Debt Instrument [Line Items]
Facility fee (as a percent)				0.30%
BAML Revolver | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate at period end (as a percent)				1.20%
BAML Revolver | LIBOR | A- | A3 | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				0.825%
BAML Revolver | LIBOR | BBB+ | Baa1
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				0.875%
BAML Revolver | LIBOR | BBB | Baa2
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				1.00%
BAML Revolver | LIBOR | BBB- | Baa3
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				1.20%
BAML Revolver | LIBOR | BBB- | Baa3 | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				1.55%
BAML Revolver | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate at period end (as a percent)				0.20%
BAML Revolver | Base Rate | A- | A3 | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				0.00%
BAML Revolver | Base Rate | BBB+ | Baa1
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				0.00%
BAML Revolver | Base Rate | BBB | Baa2
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				0.00%
BAML Revolver | Base Rate | BBB- | Baa3
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				0.20%
BAML Revolver | Base Rate | BBB- | Baa3 | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				0.55%
BAML Term Loan
Debt Instrument [Line Items]
Principal amount of loan				$ 400,000,000
Effective interest rate (as a percent)				2.47%
Additional borrowing capacity allowed by exercising an accordion feature				$ 500,000,000
Amount drawn down			$ 400,000,000
BAML Term Loan | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate at period end (as a percent)				1.35%
Fixed rate (as a percent)				1.12%
BAML Term Loan | LIBOR | A- | A3 | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				0.90%
BAML Term Loan | LIBOR | BBB+ | Baa1
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				0.95%
BAML Term Loan | LIBOR | BBB | Baa2
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				1.10%
BAML Term Loan | LIBOR | BBB- | Baa3
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				1.35%
BAML Term Loan | LIBOR | BBB- | Baa3 | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				1.75%
BAML Term Loan | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate at period end (as a percent)				0.35%
BAML Term Loan | Base Rate | A- | A3 | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				0.00%
BAML Term Loan | Base Rate | BBB+ | Baa1
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				0.00%
BAML Term Loan | Base Rate | BBB | Baa2
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				0.10%
BAML Term Loan | Base Rate | BBB- | Baa3
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				0.35%
BAML Term Loan | Base Rate | BBB- | Baa3 | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				0.75%
JPM Term Loan
Debt Instrument [Line Items]
Principal amount of loan							$ 150,000,000
Repayments of Unsecured Debt	$ 50,000,000
Unsecured term loan					$ 100,000,000
Portion of future LIBOR-based rate risk				$ 100,000,000
Number of periods of extension				2
Length of extension period				6 months
JPM Term Loan | Hedged portion
Debt Instrument [Line Items]
Portion of future LIBOR-based rate risk				$ 100,000,000
Effective interest rate (as a percent)				3.69%
JPM Term Loan | Unhedged portion
Debt Instrument [Line Items]
Weighted average interest rate (as a percent)				1.90%		3.54%
Portion of future LIBOR-based rate risk				$ 50,000,000
JPM Term Loan | Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				0.50%
JPM Term Loan | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				1.00%
Basis spread on variable rate at period end (as a percent)				1.25%
JPM Term Loan | LIBOR | Hedged portion
Debt Instrument [Line Items]
Fixed rate (as a percent)				2.44%
JPM Term Loan | LIBOR | A- | A3 | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				85.00%
JPM Term Loan | LIBOR | BBB+ | Baa1
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				90.00%
JPM Term Loan | LIBOR | BBB | Baa2
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				100.00%
JPM Term Loan | LIBOR | BBB- | Baa3
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				125.00%
JPM Term Loan | LIBOR | BBB- | Baa3 | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				165.00%
JPM Term Loan | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate at period end (as a percent)				0.25%
JPM Term Loan | Base Rate | BBB- | Baa3
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				25.00%
JPM Term Loan | Base Rate | BBB- | Baa3 | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				65.00%
BMO Term Loan
Debt Instrument [Line Items]
Principal amount of loan				$ 220,000,000
Additional loans allowed by exercising an accordion feature				$ 100,000,000
Effective interest rate (as a percent)				3.64%
BMO Term Loan | Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				0.50%
BMO Term Loan | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate at period end (as a percent)				1.25%
Fixed rate (as a percent)				2.32%
BMO Term Loan | LIBOR | Hedged portion
Debt Instrument [Line Items]
Fixed rate (as a percent)				2.39%
BMO Term Loan | LIBOR | A- | A3 | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				85.00%
BMO Term Loan | LIBOR | BBB+ | Baa1
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				90.00%
BMO Term Loan | LIBOR | BBB | Baa2
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				100.00%
BMO Term Loan | LIBOR | BBB- | Baa3
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				125.00%
BMO Term Loan | LIBOR | BBB- | Baa3 | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				165.00%
BMO Term Loan | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate at period end (as a percent)				0.25%
BMO Term Loan | Base Rate | BBB- | Baa3
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				25.00%
BMO Term Loan | Base Rate | BBB- | Baa3 | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				65.00%
BMO Term Loan | One month LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				1.00%
Tranche A Term Loan
Debt Instrument [Line Items]
Principal amount of loan				$ 55,000,000
Tranche B Term Loan
Debt Instrument [Line Items]
Principal amount of loan				$ 165,000,000

Financial Instruments_ Deriva_3

Financial Instruments: Derivatives and Hedging (Details) - USD ($) $ in Thousands	Nov. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Financial Instruments: Derivatives and Hedging
Hedged amount of portion of the future LIBOR-based rate risk		$ 17,300
Amount estimated to be reclassified into earnings within next 12 months		9,000
JPM Term Loan
Financial Instruments: Derivatives and Hedging
Hedged amount of portion of the future LIBOR-based rate risk		100,000
2017 Interest Rate Swap | Cash flow hedges
Financial Instruments: Derivatives and Hedging
Notional Value		$ 400,000
Strike Rate (as a percent)		1.12%
Fair Value		$ (2,947)	$ 3,022
2013 BMO Interest Rate Swap | Cash flow hedges
Financial Instruments: Derivatives and Hedging
Notional Value		$ 220,000
Strike Rate (as a percent)		2.32%
Fair Value			(963)
2019 JPM Interest Rate Swap | Cash flow hedges
Financial Instruments: Derivatives and Hedging
Notional Value		$ 100,000
Strike Rate (as a percent)		2.44%
Fair Value		$ (2,102)	(1,634)
2019 BMO Interest Rate Swap | Cash flow hedges
Financial Instruments: Derivatives and Hedging
Notional Value		$ 220,000
Strike Rate (as a percent)		2.39%
Fair Value		$ (12,262)	$ (5,107)
2019 BMO Interest Rate Swap | Cash flow hedges | Forecast
Financial Instruments: Derivatives and Hedging
Notional Value	$ 165,000

Financial Instruments_ Deriva_4

Financial Instruments: Derivatives and Hedging - Interest Rate Swaps (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total amount of Interest Expense presented in the consolidated statements of operations	$ 36,026	$ 36,757	$ 38,374
Interest rate swap
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total amount of Interest Expense presented in the consolidated statements of operations	36,026	36,757	38,374
Interest rate swap | Amounts of previously recorded gain/(loss) reclassified from OCI into Interest Expense
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total amount of Interest Expense presented in the consolidated statements of operations	(7,751)	4,328	2,722
Interest rate swap | Amounts of gain (loss) recognized in OCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total amount of Interest Expense presented in the consolidated statements of operations	$ (20,380)	$ (15,119)	$ 5,321

Stockholders' Equity (Details)

Stockholders' Equity (Details)	Jun. 04, 2020shares	Dec. 10, 2019shares	Jun. 04, 2020USD ($)	Dec. 31, 2020USD ($)itemshares	Dec. 31, 2019USD ($)shares	Dec. 31, 2005shares	Dec. 31, 2018shares
Stockholders' Equity
Common Stock, Shares, Outstanding				107,328,199	107,269,201
General and Administrative Expense [Member]
Equity-Based Compensation
Compensation cost | $			$ 337,000
2002 Stock Incentive Plan
Equity-Based Compensation
Maximum number of shares provided for grant under equity-based incentive compensation plan				2,000,000
Number of vesting requirements | item				0
Number of shares available for grant under the plan, Beginning				1,906,382	1,944,428
Shares Granted				(58,998)	(38,046)	(55,572)	0
Number of shares available for grant under the plan, Ending				1,847,384	1,906,382		1,944,428
Compensation Cost, Beginning | $				$ 337,000
Compensation cost | $				337,000	$ 337,000
Compensation Cost, Ending | $				$ 674,000	$ 337,000
2002 Stock Incentive Plan | Non Employee Director
Equity-Based Compensation
Shares Granted	(58,998)	(38,046)

Federal Income Tax Reporting (D

Federal Income Tax Reporting (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Federal Income Tax Reporting
Maximum ownership as a percentage of the voting power or value of the securities of each issuer other than REIT or "TRS"	10.00%
Maximum ownership of securities in all TRS (as a percent)	20.00%			25.00%
Maximum ownership of securities in all TRS when considered together with other non-real estate assets (as a percent)	25.00%
Gross amount of NOL of TRS	$ 4,600	$ 4,400
Period of statute of limitations applicable to the entity's income tax returns	3 years
Net operating losses
NOLs expiration period	20 years
Gross amount of NOLs available to company	$ 13,000	13,000	$ 13,000
Income Tax Expense
Revised Texas Franchise Tax	250	394	319
Other Taxes		(125)	41
Tax expense	250	269	$ 360
Deferred income taxes	0
Real estate assets net tax basis more (less) than book basis	$ 253,000	$ 195,000

Federal Income Tax Reporting -

Federal Income Tax Reporting - Reconciliation Between GAAP Net Income and Taxable Income, Tax Components of Distributions (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation Between GAAP Net Income and Taxable Income
Net income per GAAP	$ 37,440	$ (1,679)	$ (2,075)	$ (1,071)	$ 3,648	$ 2,399	$ 1,633	$ (1,205)	$ 32,615	$ 6,475	$ 13,069
Adjustments to GAAP net income (loss):
GAAP depreciation and amortization									88,244	90,507	93,675
Tax depreciation and amortization									(79,542)	(66,376)	(62,657)
Tax basis more than GAAP basis on assets sold									(11,450)
Straight line rent adjustment, net									(1,685)	(10,462)	(1,350)
Deferred rent, net									1,956	535	210
Non-taxable distributions											(710)
Other, net									390	4,099	(6,651)
Taxable income									30,528	24,778	35,586
Less: Capital gains recognized									7,576
Taxable income subject to distribution requirement									$ 22,952	$ 24,778	$ 35,586
Tax components of the Company's common distributions paid per share
Ordinary income (in dollars per share)									$ 0.28	$ 0.25	$ 0.35
Capital gain (in dollars per share)									0.06
Return of capital (in dollars per share)									0.02	0.11	0.11
Total (in dollars per share)									$ 0.36	$ 0.36	$ 0.46
Ordinary income (as a percent)									77.51%	69.96%	76.39%
Capital gain (as a percent)									16.72%
Return of capital (as a percent)									5.77%	30.04%	23.61%
Total (as a percent)									100.00%	100.00%	100.00%
Common Stock Dividends Per Share Cash Paid Qualified Distribution										$ 0.009
Qualified distribution as a percentage of total distribution										2.52%

Leases - Lease Costs and Maturi

Leases - Lease Costs and Maturity Analysis for Liabilities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)Option	Dec. 31, 2019USD ($)
Leases
Right-of-use asset	$ 1,400
Option to extend the terms	true
Number of options to extend | Option	1
Extension term	5 years
Lease Costs
Operating lease cost	$ 419	$ 419
Lease cost	419	419
Cash paid for amounts included in the measurement of lease liabilities	$ 421	$ 412
Weighted average remaining lease terms in years - operating leases	3 years 9 months	4 years 9 months
Weighted average discount rate - operating leases	3.86%	3.86%
Maturity analysis for liabilities
Discount rate at commencement	3.86%
2021	$ 429
2022	438
2023	447
2024	340
Total undiscounted cash flows	1,654
Present value lease liability	1,536	$ 1,890
Difference between undiscounted cash flows and discounted cash flows	$ 118

Leases - Income Relating to Lea

Leases - Income Relating to Lease Payments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income relating to lease payments:
Income from leases	$ 242,209	$ 256,250
Undiscounted Cash Flows
2021	162,676
2022	146,031
2023	138,363
2024	127,269
2025	107,596
2026 and thereafter	361,423
Income relating to lease payments	1,043,358
Variable lease payments	$ 61,310	$ 64,421

Retirement Plan (Details)

Retirement Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retirement Plan
Maximum employee compensation to be deferred per year	$ 17,000
Maximum employer matching contribution as a percentage of annual compensation	3.00%
Maximum employee salary that the employer will match	$ 200,000
Company's total contribution under 401 (k) plan	$ 100,000	$ 200,000	$ 100,000

Dispositions of Property (Detai

Dispositions of Property (Details) - USD ($) $ in Thousands	Dec. 23, 2020	Dec. 31, 2020
Dispositions of properties
Gain (loss) on sale of property		$ 41,928
Disposal group disposed of by sale, not classified as discontinued operations | Office Property In Durham North California
Dispositions of properties
Gain (loss) on sale of property	$ 41,900
Net Proceeds	$ 89,700

Subsequent Events (Details)

Subsequent Events (Details)	Jan. 15, 2021$ / shares
Cash distribution declared | Subsequent Events.
Subsequent Events
Cash dividend declared per share (in dollars per share)	$ 0.09

Selected Unaudited Quarterly _3

Selected Unaudited Quarterly Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Selected Unaudited Quarterly Information
Revenue	$ 59,810	$ 62,247	$ 60,808	$ 62,983	$ 68,997	$ 68,539	$ 66,813	$ 64,716
Net income	$ 37,440	$ (1,679)	$ (2,075)	$ (1,071)	$ 3,648	$ 2,399	$ 1,633	$ (1,205)	$ 32,615	$ 6,475	$ 13,069
Basic and diluted net income (loss) per share	$ 0.35	$ (0.02)	$ (0.02)	$ (0.01)	$ 0.03	$ 0.02	$ 0.02	$ (0.01)	$ 0.30	$ 0.06	$ 0.12
Weighted average number of shares outstanding	107,328,000	107,328,000	107,287,000	107,269,000	107,240,000	107,231,000	107,231,000	107,231,000	107,303,000	107,233,000	107,231,000

Schedule II Valuation and qua_2

Schedule II Valuation and qualifying accounts (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for doubtful accounts - Tenant rent receivables
Movement in valuation and qualifying accounts
Balance at beginning of year	$ 300,000	$ 200,000	$ 250,000
Additions (Decreases) charged to costs and expenses	340,000	213,000	128,000
Deductions	(135,000)	(113,000)	(178,000)
Balance at end of year	505,000	300,000	200,000
Allowance for doubtful accounts - Straight-line rent receivable
Movement in valuation and qualifying accounts
Balance at beginning of year	50,000	50,000	50,000
Deductions	$ (50,000)
Balance at end of year		$ 50,000	$ 50,000

SCHEDULE III REAL ESTATE AND _2

SCHEDULE III REAL ESTATE AND ACCUMULATED DEPRECIATION (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
REAL ESTATE AND ACCUMULATED DEPRECIATION
Encumbrances	$ 0
Accumulated Depreciation	538,717,000	$ 490,697,000	$ 432,579,000	$ 376,131,000
Aggregate cost for Federal Income Tax purposes	2,419,780
Real Estate Excluding Assets Held For Sale
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	189,649,000
Initial cost of Buildings Improvements and Equipment	1,556,258,000
Costs Capitalized (Disposals) Subsequent to Acquisition	394,826,000
Historical Cost of Land	189,155,000
Historical Cost of Buildings Improvements and Equipment	1,951,578,000
Total	2,140,733,000
Accumulated Depreciation	538,717,000
Total Costs, Net of Accumulated Depreciation	1,602,016,000
Forest Park, Charlotte, NC
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	1,559,000
Initial cost of Buildings Improvements and Equipment	5,672,000
Costs Capitalized (Disposals) Subsequent to Acquisition	843,000
Historical Cost of Land	1,559,000
Historical Cost of Buildings Improvements and Equipment	6,515,000
Total	8,074,000
Accumulated Depreciation	2,197,000
Total Costs, Net of Accumulated Depreciation	$ 5,877,000
Forest Park, Charlotte, NC | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Forest Park, Charlotte, NC | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Meadow Point, Chantilly, VA
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 2,634,000
Initial cost of Buildings Improvements and Equipment	18,911,000
Costs Capitalized (Disposals) Subsequent to Acquisition	8,214,000
Historical Cost of Land	2,634,000
Historical Cost of Buildings Improvements and Equipment	27,125,000
Total	29,759,000
Accumulated Depreciation	14,512,000
Total Costs, Net of Accumulated Depreciation	$ 15,247,000
Meadow Point, Chantilly, VA | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Meadow Point, Chantilly, VA | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Timberlake, Chesterfield, MO
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 2,984,000
Initial cost of Buildings Improvements and Equipment	38,661,000
Costs Capitalized (Disposals) Subsequent to Acquisition	10,549,000
Historical Cost of Land	2,984,000
Historical Cost of Buildings Improvements and Equipment	49,210,000
Total	52,194,000
Accumulated Depreciation	23,645,000
Total Costs, Net of Accumulated Depreciation	$ 28,549,000
Timberlake, Chesterfield, MO | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Timberlake, Chesterfield, MO | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Northwest Point, Elk Grove Village, IL
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 2,914,000
Initial cost of Buildings Improvements and Equipment	26,295,000
Costs Capitalized (Disposals) Subsequent to Acquisition	12,401,000
Historical Cost of Land	2,914,000
Historical Cost of Buildings Improvements and Equipment	38,696,000
Total	41,610,000
Accumulated Depreciation	19,497,000
Total Costs, Net of Accumulated Depreciation	$ 22,113,000
Northwest Point, Elk Grove Village, IL | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Northwest Point, Elk Grove Village, IL | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Timberlake East, Chesterfield, MO
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 2,626,000
Initial cost of Buildings Improvements and Equipment	17,608,000
Costs Capitalized (Disposals) Subsequent to Acquisition	5,377,000
Historical Cost of Land	2,626,000
Historical Cost of Buildings Improvements and Equipment	22,985,000
Total	25,611,000
Accumulated Depreciation	11,052,000
Total Costs, Net of Accumulated Depreciation	$ 14,559,000
Timberlake East, Chesterfield, MO | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Timberlake East, Chesterfield, MO | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Park Ten, Houston, TX
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 1,061,000
Initial cost of Buildings Improvements and Equipment	21,303,000
Costs Capitalized (Disposals) Subsequent to Acquisition	6,899,000
Historical Cost of Land	567,000
Historical Cost of Buildings Improvements and Equipment	28,696,000
Total	29,263,000
Accumulated Depreciation	13,225,000
Total Costs, Net of Accumulated Depreciation	$ 16,038,000
Park Ten, Houston, TX | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Park Ten, Houston, TX | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Addison, Addison, TX
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 4,325,000
Initial cost of Buildings Improvements and Equipment	48,040,000
Costs Capitalized (Disposals) Subsequent to Acquisition	12,106,000
Historical Cost of Land	4,325,000
Historical Cost of Buildings Improvements and Equipment	60,146,000
Total	64,471,000
Accumulated Depreciation	23,625,000
Total Costs, Net of Accumulated Depreciation	$ 40,846,000
Addison, Addison, TX | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Addison, Addison, TX | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Collins, Richardson, TX
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 4,000,000
Initial cost of Buildings Improvements and Equipment	42,598,000
Costs Capitalized (Disposals) Subsequent to Acquisition	8,497,000
Historical Cost of Land	4,000,000
Historical Cost of Buildings Improvements and Equipment	51,095,000
Total	55,095,000
Accumulated Depreciation	23,307,000
Total Costs, Net of Accumulated Depreciation	$ 31,788,000
Collins, Richardson, TX | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Collins, Richardson, TX | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Greenwood, Englewood, CO
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 3,100,000
Initial cost of Buildings Improvements and Equipment	30,201,000
Costs Capitalized (Disposals) Subsequent to Acquisition	11,770,000
Historical Cost of Land	3,100,000
Historical Cost of Buildings Improvements and Equipment	41,971,000
Total	45,071,000
Accumulated Depreciation	18,663,000
Total Costs, Net of Accumulated Depreciation	$ 26,408,000
Greenwood, Englewood, CO | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Greenwood, Englewood, CO | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
River Crossing, Indianapolis, IN
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 3,000,000
Initial cost of Buildings Improvements and Equipment	36,926,000
Costs Capitalized (Disposals) Subsequent to Acquisition	6,448,000
Historical Cost of Land	3,000,000
Historical Cost of Buildings Improvements and Equipment	43,374,000
Total	46,374,000
Accumulated Depreciation	16,740,000
Total Costs, Net of Accumulated Depreciation	$ 29,634,000
River Crossing, Indianapolis, IN | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
River Crossing, Indianapolis, IN | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Innsbrook, Glenn Allen, VA
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 5,000,000
Initial cost of Buildings Improvements and Equipment	40,216,000
Costs Capitalized (Disposals) Subsequent to Acquisition	8,945,000
Historical Cost of Land	5,000,000
Historical Cost of Buildings Improvements and Equipment	49,161,000
Total	54,161,000
Accumulated Depreciation	19,141,000
Total Costs, Net of Accumulated Depreciation	$ 35,020,000
Innsbrook, Glenn Allen, VA | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Innsbrook, Glenn Allen, VA | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
380 Interlocken, Bloomfield, CO
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 8,275,000
Initial cost of Buildings Improvements and Equipment	34,462,000
Costs Capitalized (Disposals) Subsequent to Acquisition	12,624,000
Historical Cost of Land	8,275,000
Historical Cost of Buildings Improvements and Equipment	47,086,000
Total	55,361,000
Accumulated Depreciation	17,122,000
Total Costs, Net of Accumulated Depreciation	$ 38,239,000
380 Interlocken, Bloomfield, CO | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
380 Interlocken, Bloomfield, CO | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Blue Lagoon, Miami, FL
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 6,306,000
Initial cost of Buildings Improvements and Equipment	46,124,000
Costs Capitalized (Disposals) Subsequent to Acquisition	18,068,000
Historical Cost of Land	6,306,000
Historical Cost of Buildings Improvements and Equipment	64,192,000
Total	70,498,000
Accumulated Depreciation	14,998,000
Total Costs, Net of Accumulated Depreciation	$ 55,500,000
Blue Lagoon, Miami, FL | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Blue Lagoon, Miami, FL | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Eldridge Green, Houston, TX
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 3,900,000
Initial cost of Buildings Improvements and Equipment	43,791,000
Costs Capitalized (Disposals) Subsequent to Acquisition	5,548,000
Historical Cost of Land	3,900,000
Historical Cost of Buildings Improvements and Equipment	49,339,000
Total	53,239,000
Accumulated Depreciation	19,925,000
Total Costs, Net of Accumulated Depreciation	$ 33,314,000
Eldridge Green, Houston, TX | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Eldridge Green, Houston, TX | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Liberty Plaza, Addison, TX
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 4,374,000
Initial cost of Buildings Improvements and Equipment	21,146,000
Costs Capitalized (Disposals) Subsequent to Acquisition	8,976,000
Historical Cost of Land	4,374,000
Historical Cost of Buildings Improvements and Equipment	30,122,000
Total	34,496,000
Accumulated Depreciation	12,090,000
Total Costs, Net of Accumulated Depreciation	$ 22,406,000
Liberty Plaza, Addison, TX | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Liberty Plaza, Addison, TX | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
One Overton, Atlanta, GA
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 3,900,000
Initial cost of Buildings Improvements and Equipment	77,229,000
Costs Capitalized (Disposals) Subsequent to Acquisition	17,781,000
Historical Cost of Land	3,900,000
Historical Cost of Buildings Improvements and Equipment	95,010,000
Total	98,910,000
Accumulated Depreciation	37,025,000
Total Costs, Net of Accumulated Depreciation	$ 61,885,000
One Overton, Atlanta, GA | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
One Overton, Atlanta, GA | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
FSP 390 Interlocken, Broomfield, CO
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 7,013,000
Initial cost of Buildings Improvements and Equipment	37,751,000
Costs Capitalized (Disposals) Subsequent to Acquisition	14,197,000
Historical Cost of Land	7,013,000
Historical Cost of Buildings Improvements and Equipment	51,948,000
Total	58,961,000
Accumulated Depreciation	18,480,000
Total Costs, Net of Accumulated Depreciation	$ 40,481,000
FSP 390 Interlocken, Broomfield, CO | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
FSP 390 Interlocken, Broomfield, CO | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Park Ten II, Houston, TX
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 1,300,000
Initial cost of Buildings Improvements and Equipment	31,712,000
Costs Capitalized (Disposals) Subsequent to Acquisition	6,979,000
Historical Cost of Land	1,300,000
Historical Cost of Buildings Improvements and Equipment	38,691,000
Total	39,991,000
Accumulated Depreciation	11,764,000
Total Costs, Net of Accumulated Depreciation	$ 28,227,000
Park Ten II, Houston, TX | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Park Ten II, Houston, TX | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Dulles Virginia, Sterling, VA
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 4,813,000
Initial cost of Buildings Improvements and Equipment	13,285,000
Costs Capitalized (Disposals) Subsequent to Acquisition	6,714,000
Historical Cost of Land	4,813,000
Historical Cost of Buildings Improvements and Equipment	19,999,000
Total	24,812,000
Accumulated Depreciation	7,295,000
Total Costs, Net of Accumulated Depreciation	$ 17,517,000
Dulles Virginia, Sterling, VA | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Dulles Virginia, Sterling, VA | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Stonecroft, Chantilly, VA
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 2,102,000
Initial cost of Buildings Improvements and Equipment	18,003,000
Costs Capitalized (Disposals) Subsequent to Acquisition	1,814,000
Historical Cost of Land	2,102,000
Historical Cost of Buildings Improvements and Equipment	19,817,000
Total	21,919,000
Accumulated Depreciation	5,116,000
Total Costs, Net of Accumulated Depreciation	$ 16,803,000
Stonecroft, Chantilly, VA | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Stonecroft, Chantilly, VA | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
121 South Eight Street, Minneapolis, MN
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 4,444,000
Initial cost of Buildings Improvements and Equipment	15,214,000
Costs Capitalized (Disposals) Subsequent to Acquisition	24,592,000
Historical Cost of Land	4,444,000
Historical Cost of Buildings Improvements and Equipment	39,806,000
Total	44,250,000
Accumulated Depreciation	10,917,000
Total Costs, Net of Accumulated Depreciation	$ 33,333,000
121 South Eight Street, Minneapolis, MN | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
121 South Eight Street, Minneapolis, MN | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
801 Marquette Avenue South, Minneapolis, MN
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 4,184,000
Costs Capitalized (Disposals) Subsequent to Acquisition	22,295,000
Historical Cost of Land	4,184,000
Historical Cost of Buildings Improvements and Equipment	22,295,000
Total	26,479,000
Accumulated Depreciation	1,836,000
Total Costs, Net of Accumulated Depreciation	$ 24,643,000
801 Marquette Avenue South, Minneapolis, MN | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
801 Marquette Avenue South, Minneapolis, MN | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
909 Davis, Evanston, IL
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 4,912,000
Initial cost of Buildings Improvements and Equipment	18,229,000
Costs Capitalized (Disposals) Subsequent to Acquisition	8,112,000
Historical Cost of Land	4,912,000
Historical Cost of Buildings Improvements and Equipment	26,341,000
Total	31,253,000
Accumulated Depreciation	6,985,000
Total Costs, Net of Accumulated Depreciation	$ 24,268,000
909 Davis, Evanston, IL | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
909 Davis, Evanston, IL | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Legacy Tennyson Center, Plano, TX
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 3,067,000
Initial cost of Buildings Improvements and Equipment	22,064,000
Costs Capitalized (Disposals) Subsequent to Acquisition	3,411,000
Historical Cost of Land	3,067,000
Historical Cost of Buildings Improvements and Equipment	25,475,000
Total	28,542,000
Accumulated Depreciation	6,390,000
Total Costs, Net of Accumulated Depreciation	$ 22,152,000
Legacy Tennyson Center, Plano, TX | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Legacy Tennyson Center, Plano, TX | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
One Legacy Circle, Plano, TX
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 2,590,000
Initial cost of Buildings Improvements and Equipment	36,608,000
Costs Capitalized (Disposals) Subsequent to Acquisition	3,783,000
Historical Cost of Land	2,590,000
Historical Cost of Buildings Improvements and Equipment	40,391,000
Total	42,981,000
Accumulated Depreciation	10,600,000
Total Costs, Net of Accumulated Depreciation	$ 32,381,000
One Legacy Circle, Plano, TX | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
One Legacy Circle, Plano, TX | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
One Ravinia Drive, Atlanta, GA
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 2,686,000
Initial cost of Buildings Improvements and Equipment	35,125,000
Costs Capitalized (Disposals) Subsequent to Acquisition	12,471,000
Historical Cost of Land	2,686,000
Historical Cost of Buildings Improvements and Equipment	47,596,000
Total	50,282,000
Accumulated Depreciation	10,821,000
Total Costs, Net of Accumulated Depreciation	$ 39,461,000
One Ravinia Drive, Atlanta, GA | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
One Ravinia Drive, Atlanta, GA | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Two Ravinia Drive, Atlanta, GA
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 7,375,000
Initial cost of Buildings Improvements and Equipment	58,726,000
Costs Capitalized (Disposals) Subsequent to Acquisition	12,259,000
Historical Cost of Land	7,375,000
Historical Cost of Buildings Improvements and Equipment	70,985,000
Total	78,360,000
Accumulated Depreciation	11,630,000
Total Costs, Net of Accumulated Depreciation	$ 66,730,000
Two Ravinia Drive, Atlanta, GA | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Two Ravinia Drive, Atlanta, GA | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Westchase I & II, Houston, TX
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 8,491,000
Initial cost of Buildings Improvements and Equipment	121,508,000
Costs Capitalized (Disposals) Subsequent to Acquisition	14,548,000
Historical Cost of Land	8,491,000
Historical Cost of Buildings Improvements and Equipment	136,056,000
Total	144,547,000
Accumulated Depreciation	29,975,000
Total Costs, Net of Accumulated Depreciation	$ 114,572,000
Westchase I & II, Houston, TX | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Westchase I & II, Houston, TX | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
1999 Broadway, Denver, CO
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 16,334,000
Initial cost of Buildings Improvements and Equipment	137,726,000
Costs Capitalized (Disposals) Subsequent to Acquisition	38,338,000
Historical Cost of Land	16,334,000
Historical Cost of Buildings Improvements and Equipment	176,064,000
Total	192,398,000
Accumulated Depreciation	34,199,000
Total Costs, Net of Accumulated Depreciation	$ 158,199,000
1999 Broadway, Denver, CO | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
1999 Broadway, Denver, CO | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
999 Peachtree, Atlanta, GA
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 10,187,000
Initial cost of Buildings Improvements and Equipment	107,727,000
Costs Capitalized (Disposals) Subsequent to Acquisition	23,820,000
Historical Cost of Land	10,187,000
Historical Cost of Buildings Improvements and Equipment	131,547,000
Total	141,734,000
Accumulated Depreciation	25,096,000
Total Costs, Net of Accumulated Depreciation	$ 116,638,000
999 Peachtree, Atlanta, GA | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
999 Peachtree, Atlanta, GA | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
1001 17th Street, Denver, CO
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 17,413,000
Initial cost of Buildings Improvements and Equipment	165,058,000
Costs Capitalized (Disposals) Subsequent to Acquisition	22,284,000
Historical Cost of Land	17,413,000
Historical Cost of Buildings Improvements and Equipment	187,342,000
Total	204,755,000
Accumulated Depreciation	35,495,000
Total Costs, Net of Accumulated Depreciation	$ 169,260,000
1001 17th Street, Denver, CO | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
1001 17th Street, Denver, CO | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Plaza Seven, Minneapolis, MN
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 6,604,000
Initial cost of Buildings Improvements and Equipment	54,240,000
Costs Capitalized (Disposals) Subsequent to Acquisition	11,073,000
Historical Cost of Land	6,604,000
Historical Cost of Buildings Improvements and Equipment	65,313,000
Total	71,917,000
Accumulated Depreciation	9,175,000
Total Costs, Net of Accumulated Depreciation	$ 62,742,000
Plaza Seven, Minneapolis, MN | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Plaza Seven, Minneapolis, MN | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
Pershing Plaza, Atlanta, GA
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 5,300,000
Initial cost of Buildings Improvements and Equipment	34,158,000
Costs Capitalized (Disposals) Subsequent to Acquisition	2,040,000
Historical Cost of Land	5,300,000
Historical Cost of Buildings Improvements and Equipment	36,198,000
Total	41,498,000
Accumulated Depreciation	4,110,000
Total Costs, Net of Accumulated Depreciation	$ 37,388,000
Pershing Plaza, Atlanta, GA | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
Pershing Plaza, Atlanta, GA | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years
600 17th Street, Denver, Co
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	$ 20,876,000
Initial cost of Buildings Improvements and Equipment	99,941,000
Costs Capitalized (Disposals) Subsequent to Acquisition	11,050,000
Historical Cost of Land	20,876,000
Historical Cost of Buildings Improvements and Equipment	110,991,000
Total	131,867,000
Accumulated Depreciation	12,069,000
Total Costs, Net of Accumulated Depreciation	$ 119,798,000
600 17th Street, Denver, Co | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	5 years
600 17th Street, Denver, Co | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Depreciable Life Years	39 years

SCHEDULE III REAL ESTATE AND _3

SCHEDULE III REAL ESTATE AND ACCUMULATED DEPRECIATION - Changes in real estate investments and accumulated depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Real estate investments, at cost:
Balance, beginning of year	$ 2,127,907	$ 2,058,352	$ 2,008,823
Improvements	75,472	74,324	53,279
Dispositions	(62,646)	(4,769)	(3,750)
Balance, end of year	2,140,733	2,127,907	2,058,352
Accumulated depreciation:
Balance, beginning of year	490,697	432,579	376,131
Depreciation	67,001	62,887	60,198
Dispositions	(18,981)	(4,769)	(3,750)
Balance, end of year	$ 538,717	$ 490,697	$ 432,579