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Related Party Transactions and Investments in Non-Consolidated Entities - Investment in Sponsored REITs - Property Sold (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2017 USD ($) entity
Investment in Sponsored REITs
Number of properties sold | entity		1
FSP 1441 Main Street Corp.
Investment in Sponsored REITs
Repayment of principal		$ 9.0
FSP Energy Tower I Corp.
Investment in Sponsored REITs
Repayment of principal	$ 51.0

X

- Definition

Represents the number of properties owned by sponsored REITs which were sold during the period.

+ References

No definition available.

+ Details

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- Definition

The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3291-108585

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Details

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