Investments in Joint Ventures as of December 31, 2020 (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Investments in real estate, net.	$ 412,178	$ 451,767
Cash and cash equivalents	9,478	21,649
Unrealized rents & receivables	1,612	1,102
Deferred costs	3,448	4,038
Total Assets	681,252	536,360
Secured notes payable	169,372	180,890
Other liabilities	29,646	34,126
Capital - Third Parties	396,561	367,654
Total Liabilities and Capital	681,252	536,360
Real Estate Total Assets [Member]
Schedule of Equity Method Investments [Line Items]
Total Assets	426,716	478,556
Real Estate Partnership F R P [Member]
Schedule of Equity Method Investments [Line Items]
Capital - FRP	140,639	174,792
Real Estate Partnership Third Parties [Member]
Schedule of Equity Method Investments [Line Items]
Capital - Third Parties	87,059	88,748
Real Estate Partnership Total Liabilities And Capital [Member]
Schedule of Equity Method Investments [Line Items]
Total Liabilities and Capital	426,716	478,556
Brooksville Quarry L L C [Member]
Schedule of Equity Method Investments [Line Items]
Investments in real estate, net.	14,284	14,287
Cash and cash equivalents	55	55
Unrealized rents & receivables	0	0
Deferred costs	1	5
Secured notes payable	0	0
Other liabilities	68	28
Brooksville Quarry L L C [Member] | Real Estate Total Assets [Member]
Schedule of Equity Method Investments [Line Items]
Total Assets	14,340	14,347
Brooksville Quarry L L C [Member] | Real Estate Partnership F R P [Member]
Schedule of Equity Method Investments [Line Items]
Capital - FRP	7,474	7,499
Brooksville Quarry L L C [Member] | Real Estate Partnership Third Parties [Member]
Schedule of Equity Method Investments [Line Items]
Capital - Third Parties	6,798	6,820
Brooksville Quarry L L C [Member] | Real Estate Partnership Total Liabilities And Capital [Member]
Schedule of Equity Method Investments [Line Items]
Total Liabilities and Capital	14,340	14,347
B C F R P Realty L L C [Member]
Schedule of Equity Method Investments [Line Items]
Investments in real estate, net.	21,754	22,067
Cash and cash equivalents	310	90
Unrealized rents & receivables	444	254
Deferred costs	238	336
Secured notes payable	11,764	12,370
Other liabilities	126	123
B C F R P Realty L L C [Member] | Real Estate Total Assets [Member]
Schedule of Equity Method Investments [Line Items]
Total Assets	22,746	22,747
B C F R P Realty L L C [Member] | Real Estate Partnership F R P [Member]
Schedule of Equity Method Investments [Line Items]
Capital - FRP	5,428	5,127
B C F R P Realty L L C [Member] | Real Estate Partnership Third Parties [Member]
Schedule of Equity Method Investments [Line Items]
Capital - Third Parties	5,428	5,127
B C F R P Realty L L C [Member] | Real Estate Partnership Total Liabilities And Capital [Member]
Schedule of Equity Method Investments [Line Items]
Total Liabilities and Capital	22,746	22,747
Hyde Park [Member]
Schedule of Equity Method Investments [Line Items]
Investments in real estate, net.	4	591
Cash and cash equivalents	0	0
Unrealized rents & receivables	0	0
Deferred costs	0	0
Secured notes payable	0	0
Other liabilities	0	0
Hyde Park [Member] | Real Estate Total Assets [Member]
Schedule of Equity Method Investments [Line Items]
Total Assets	4	591
Hyde Park [Member] | Real Estate Partnership F R P [Member]
Schedule of Equity Method Investments [Line Items]
Capital - FRP	4	591
Hyde Park [Member] | Real Estate Partnership Third Parties [Member]
Schedule of Equity Method Investments [Line Items]
Capital - Third Parties	0	0
Hyde Park [Member] | Real Estate Partnership Total Liabilities And Capital [Member]
Schedule of Equity Method Investments [Line Items]
Total Liabilities and Capital	4	591
Amber Ridge Loan [Member]
Schedule of Equity Method Investments [Line Items]
Investments in real estate, net.	11,859	10,026
Cash and cash equivalents	0	0
Unrealized rents & receivables	0	0
Deferred costs	0	0
Secured notes payable	0	0
Other liabilities	0	0
Amber Ridge Loan [Member] | Real Estate Total Assets [Member]
Schedule of Equity Method Investments [Line Items]
Total Assets	11,859	10,026
Amber Ridge Loan [Member] | Real Estate Partnership F R P [Member]
Schedule of Equity Method Investments [Line Items]
Capital - FRP	11,859	10,026
Amber Ridge Loan [Member] | Real Estate Partnership Third Parties [Member]
Schedule of Equity Method Investments [Line Items]
Capital - Third Parties	0	0
Amber Ridge Loan [Member] | Real Estate Partnership Total Liabilities And Capital [Member]
Schedule of Equity Method Investments [Line Items]
Total Liabilities and Capital	11,859	10,026
Apartment Mixed Use [Member]
Schedule of Equity Method Investments [Line Items]
Investments in real estate, net.	364,277	404,796
Cash and cash equivalents	9,113	21,504
Unrealized rents & receivables	1,168	848
Deferred costs	3,209	3,697
Secured notes payable	157,608	168,520
Other liabilities	29,452	33,975
Apartment Mixed Use [Member] | Real Estate Total Assets [Member]
Schedule of Equity Method Investments [Line Items]
Total Assets	377,767	430,845
Apartment Mixed Use [Member] | Real Estate Partnership F R P [Member]
Schedule of Equity Method Investments [Line Items]
Capital - FRP	115,874	151,549
Apartment Mixed Use [Member] | Real Estate Partnership Third Parties [Member]
Schedule of Equity Method Investments [Line Items]
Capital - Third Parties	74,833	76,801
Apartment Mixed Use [Member] | Real Estate Partnership Total Liabilities And Capital [Member]
Schedule of Equity Method Investments [Line Items]
Total Liabilities and Capital	$ 377,767	$ 430,845