Represents the period from the maturity date of the debt for which the debt facility can be extended.

No definition available.

Name:	fsp_DebtInstrumentExtensionPeriod
Namespace Prefix:	fsp_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the leverage ratio that is calculated by dividing consolidated funded debt (including financial letters of credit) by consolidated earnings before interest, taxes, depreciation, and amortization (EBITDA) as of the reporting period date.

+ References

No definition available.

+ Details

Name:	fsp_DebtInstrumentLeverageRatio
Namespace Prefix:	fsp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the amount of maximum borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	fsp_DebtInstrumentMaximumBorrowingCapacity
Namespace Prefix:	fsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The increase in the maximum borrowing capacity under the long-term financing arrangement, upon exercise of the accordion feature which is subject to receipt of lender commitments and satisfaction of certain customary conditions.

+ References

No definition available.

+ Details

Name:	fsp_DebtInstrumentMaximumBorrowingCapacityIncreaseAfterAccordionFeature
Namespace Prefix:	fsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The increase in the maximum borrowing capacity under the credit facility upon exercise of the accordion feature which is subject to receipt of lender commitments and satisfaction of certain customary conditions.

+ References

No definition available.

+ Details

Name:	fsp_LineOfCreditFacilityMaximumBorrowingCapacityIncreaseAfterAccordionFeature
Namespace Prefix:	fsp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentDescriptionOfVariableRateBasis
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The effective interest rate at the end of the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateAtPeriodEnd
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Fixed interest rate related to the interest rate derivative.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeFixedInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.16)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 20, 22

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The effective interest rate at the end of the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

Name:	us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The effective interest rate during the reporting period.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityInterestRateDuringPeriod
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash inflow from the issuance of long-term debt that is not secured by collateral. Excludes proceeds from tax exempt unsecured debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 14

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3255-108585

+ Details

Name:	us-gaap_ProceedsFromIssuanceOfUnsecuredDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Bank note payable (Details) (USD $)	9 Months Ended			0 Months Ended		9 Months Ended																																																													9 Months Ended		9 Months Ended
Bank note payable (Details) (USD $)	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Aug. 26, 2013 2013 Term Loan	Sep. 30, 2013 2013 Term Loan	Sep. 30, 2013 2013 Term Loan Minimum Greater than 25% to less than or equal to 35%	Sep. 30, 2013 2013 Term Loan Minimum Greater than 35% to less than or equal to 45%	Sep. 30, 2013 2013 Term Loan Minimum Greater than 45% to less than or equal to 55%	Sep. 30, 2013 2013 Term Loan Minimum Greater than 55%	Sep. 30, 2013 2013 Term Loan Maximum Less than or equal to 25%	Sep. 30, 2013 2013 Term Loan Maximum Greater than 25% to less than or equal to 35%	Sep. 30, 2013 2013 Term Loan Maximum Greater than 35% to less than or equal to 45%	Sep. 30, 2013 2013 Term Loan Maximum Greater than 45% to less than or equal to 55%	Sep. 30, 2013 2013 Term Loan LIBOR	Sep. 30, 2013 2013 Term Loan LIBOR Less than or equal to 25%	Sep. 30, 2013 2013 Term Loan LIBOR Greater than 25% to less than or equal to 35%	Sep. 30, 2013 2013 Term Loan LIBOR Greater than 35% to less than or equal to 45%	Sep. 30, 2013 2013 Term Loan LIBOR Greater than 45% to less than or equal to 55%	Sep. 30, 2013 2013 Term Loan LIBOR Greater than 55%	Sep. 30, 2013 2013 Term Loan LIBOR Minimum	Sep. 30, 2013 2013 Term Loan LIBOR Maximum	Sep. 30, 2013 2013 Term Loan Bank's base rate	Sep. 30, 2013 2013 Term Loan Bank's base rate Less than or equal to 25%	Sep. 30, 2013 2013 Term Loan Bank's base rate Greater than 25% to less than or equal to 35%	Sep. 30, 2013 2013 Term Loan Bank's base rate Greater than 35% to less than or equal to 45%	Sep. 30, 2013 2013 Term Loan Bank's base rate Greater than 45% to less than or equal to 55%	Sep. 30, 2013 2013 Term Loan Bank's base rate Greater than 55%	Sep. 30, 2013 2013 Term Loan Bank's base rate Minimum	Sep. 30, 2013 2013 Term Loan Bank's base rate Maximum	Sep. 30, 2013 2012 Credit Facility	Sep. 30, 2013 2012 Credit Facility Less than or equal to 25%	Sep. 30, 2013 2012 Credit Facility Greater than 25% to less than or equal to 35%	Sep. 30, 2013 2012 Credit Facility Greater than 35% to less than or equal to 45%	Sep. 30, 2013 2012 Credit Facility Greater than 45% to less than or equal to 55%	Sep. 30, 2013 2012 Credit Facility Greater than 55%	Sep. 30, 2013 2012 Credit Facility Minimum	Sep. 30, 2013 2012 Credit Facility Minimum Greater than 25% to less than or equal to 35%	Sep. 30, 2013 2012 Credit Facility Minimum Greater than 35% to less than or equal to 45%	Sep. 30, 2013 2012 Credit Facility Minimum Greater than 45% to less than or equal to 55%	Sep. 30, 2013 2012 Credit Facility Minimum Greater than 55%	Sep. 30, 2013 2012 Credit Facility Maximum	Sep. 30, 2013 2012 Credit Facility Maximum Less than or equal to 25%	Sep. 30, 2013 2012 Credit Facility Maximum Greater than 25% to less than or equal to 35%	Sep. 30, 2013 2012 Credit Facility Maximum Greater than 35% to less than or equal to 45%	Sep. 30, 2013 2012 Credit Facility Maximum Greater than 45% to less than or equal to 55%	Sep. 30, 2013 2012 Credit Facility LIBOR	Sep. 30, 2013 2012 Credit Facility LIBOR Less than or equal to 25%	Sep. 30, 2013 2012 Credit Facility LIBOR Greater than 25% to less than or equal to 35%	Sep. 30, 2013 2012 Credit Facility LIBOR Greater than 35% to less than or equal to 45%	Sep. 30, 2013 2012 Credit Facility LIBOR Greater than 45% to less than or equal to 55%	Sep. 30, 2013 2012 Credit Facility LIBOR Greater than 55%	Sep. 30, 2013 2012 Credit Facility LIBOR Minimum	Sep. 30, 2013 2012 Credit Facility LIBOR Maximum	Sep. 30, 2013 2012 Credit Facility Bank's base rate	Sep. 30, 2013 2012 Credit Facility Bank's base rate Less than or equal to 25%	Sep. 30, 2013 2012 Credit Facility Bank's base rate Greater than 25% to less than or equal to 35%	Sep. 30, 2013 2012 Credit Facility Bank's base rate Greater than 35% to less than or equal to 45%	Sep. 30, 2013 2012 Credit Facility Bank's base rate Greater than 45% to less than or equal to 55%	Sep. 30, 2013 2012 Credit Facility Bank's base rate Greater than 55%	Sep. 30, 2013 2012 Credit Facility Bank's base rate Minimum	Sep. 30, 2013 2012 Credit Facility Bank's base rate Maximum	Sep. 30, 2013 2012 Credit Facility Federal funds rate	Sep. 30, 2013 2012 Credit Facility One month LIBOR	Sep. 30, 2013 2012 Revolver	Dec. 31, 2012 2012 Revolver	Sep. 27, 2012 2012 Revolver	Sep. 30, 2013 2012 Term Loan	Sep. 27, 2012 2012 Term Loan	Sep. 30, 2013 2012 Term Loan LIBOR	Sep. 27, 2012 2011 Revolver
Bank note and term note payable
Maximum borrowing capacity				$ 220,000,000
Amount drawn down	220,000,000	400,000,000		220,000,000
Term of the borrowing				7 years																																																												4 years			5 years
Additional loans allowed by exercising an accordion feature				50,000,000
Variable base rate														LIBOR								Bank's base rate																								LIBOR								Bank's base rate								Federal Funds Rate	One month LIBOR						LIBOR
Debt instrument overall rate (basis spread plus variable rate), end of period (as a percent)					3.77%									1.63%								3.70%
Total available																														900,000,000																																		500,000,000			400,000,000			600,000,000
Borrowings outstanding	331,500,000		216,750,000																																																													331,500,000	216,750,000	82,000,000		400,000,000		482,000,000
Additional borrowing capacity allowed by exercising an accordion feature																																																																$ 250,000,000
Extension available on debt																																																																12 months
Basis spread on variable rate (as a percent)														1.45%	1.45%	1.55%	1.65%	1.90%	2.20%	1.45%	2.20%	0.45%	0.45%	0.55%	0.65%	0.90%	1.20%	0.45%	1.20%																	1.40%	1.35%	1.40%	1.45%	1.65%	1.90%	1.35%	1.90%	0.40%	0.35%	0.40%	0.45%	0.65%	0.90%	0.35%	0.90%	0.50%	1.00%
Fixed rate (as a percent)														2.32%																																																							0.75%
Overall rate (basis spread plus variable rate), end of period (as a percent)																																														1.58%								3.65%										1.65%	2.23%		2.20%
Weighted average rate interest rate, during period (as a percent)																																																																1.63%
Leverage Ratio (as a percent)						25.00%	35.00%	45.00%	55.00%	25.00%	35.00%	45.00%	55.00%																								25.00%	35.00%	45.00%	55.00%		25.00%	35.00%	45.00%	55.00%
Facility fee (as a percent)																														0.25%	0.20%	0.25%	0.30%	0.35%	0.40%	0.20%					0.40%