Investments in Joint Ventures (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Jul. 31, 2019	Dec. 24, 2018	May 04, 2018	Apr. 26, 2016	Oct. 04, 2006
Total Investment	$ 167,586		$ 167,586		$ 160,452
Total Assets of the Partnership	456,652		456,652		334,742
Profit (Loss) of the Partnership			(3,551)		(1,201)
Company's share of Net Loss of the Partnership	(1,788)	$ (746)	(3,773)	$ (1,282)	(1,954)
Investments in real estate, net	418,495		418,495		287,106
Cash and cash equivalents	32,965		32,965		45,909
Deferred costs	4,069		4,069		821
Unrealized rents & receivable	1,123		1,123		906
Secured notes payable	162,421		162,421		81,573
Other liabilities	31,243		31,243		27,524
Capital - FRP	175,728		175,728		170,832
Capital - Third parties	87,260		87,260		54,813
Total liabilities and capital	$ 456,652		$ 456,652		$ 334,742
Brooksville Quarry, LLC
Ownership percent	50.00%		50.00%		50.00%					50.00%
Total Investment	$ 7,463		$ 7,463		$ 7,499
Total Assets of the Partnership	14,306		14,306		14,316
Profit (Loss) of the Partnership			(66)		(84)
Company's share of Net Loss of the Partnership			(33)		(42)
Investments in real estate, net	14,289		14,289		14,293
Cash and cash equivalents	17		17		18
Deferred costs	0		0		5
Unrealized rents & receivable	0		0		0
Secured notes payable	0		0		0
Other liabilities	62		62		2
Capital - FRP	7,463		7,463		7,500
Capital - Third parties	6,781		6,781		6,814
Total liabilities and capital	$ 14,306		$ 14,306		$ 14,316
BC FRP Realty, LLC
Ownership percent	50.00%		50.00%		50.00%				50.00%
Total Investment	$ 5,233		$ 5,233		$ 5,391
Total Assets of the Partnership	22,726		22,726		22,969
Profit (Loss) of the Partnership			(311)		(1,114)
Company's share of Net Loss of the Partnership			(157)		(591)
Investments in real estate, net	22,063		22,063		22,423
Cash and cash equivalents	82		82		15
Deferred costs	346		346		311
Unrealized rents & receivable	235		235		220
Secured notes payable	12,268		12,268		12,103
Other liabilities	104		104		196
Capital - FRP	5,177		5,177		5,335
Capital - Third parties	5,177		5,177		5,335
Total liabilities and capital	$ 22,726		$ 22,726		$ 22,969
RiverFront Holdings II, LLC
Ownership percent	80.00%		80.00%		80.00%			80.00%
Total Investment	$ 24,429		$ 24,429		$ 25,975
Total Assets of the Partnership	106,289		106,289		88,235
Profit (Loss) of the Partnership			(3,116)		(95)
Company's share of Net Loss of the Partnership			(2,749)		(871)
Investments in real estate, net	104,647		104,647		87,521
Cash and cash equivalents	1,330		1,330		630
Deferred costs	231		231		2
Unrealized rents & receivable	81		81		82
Secured notes payable	63,082		63,082		38,564
Other liabilities	2,670		2,670		6,771
Capital - FRP	35,550		35,550		37,284
Capital - Third parties	4,987		4,987		5,616
Total liabilities and capital	$ 106,289		$ 106,289		$ 88,235
Bryant Street Partnerships
Ownership percent	61.36%		61.36%		61.36%		61.36%
Total Investment	$ 60,059		$ 60,059		$ 58,353
Total Assets of the Partnership	156,638		156,638		96,477
Profit (Loss) of the Partnership			(126)		260
Company's share of Net Loss of the Partnership			(1,317)		(573)
Investments in real estate, net	156,022		156,022		95,903
Cash and cash equivalents	483		483		387
Deferred costs	23		23		29
Unrealized rents & receivable	110		110		158
Secured notes payable	57,792		57,792		1,660
Other liabilities	20,213		20,213		17,183
Capital - FRP	58,527		58,527		57,479
Capital - Third parties	20,106		20,106		20,155
Total liabilities and capital	156,638		156,638		96,477
Hyde Park
Total Investment	591		591		3,492
Total Assets of the Partnership	591		591		3,492
Profit (Loss) of the Partnership			0		0
Company's share of Net Loss of the Partnership			0		0
Investments in real estate, net	591		591		3,492
Cash and cash equivalents	0		0		0
Deferred costs	0		0		0
Unrealized rents & receivable	0		0		0
Secured notes payable	0		0		0
Other liabilities	0		0		0
Capital - FRP	591		591		3,492
Capital - Third parties	0		0		0
Total liabilities and capital	$ 591		$ 591		$ 3,492
DST Hickory Creek
Ownership percent	26.65%		26.65%		26.65%	26.65%
Total Investment	$ 6,000		$ 6,000		$ 6,000
Total Assets of the Partnership	48,303		48,303		49,369
Profit (Loss) of the Partnership			(255)		(168)
Company's share of Net Loss of the Partnership			254		123
Investments in real estate, net	45,787		45,787		46,685
Cash and cash equivalents	1,397		1,397		1,764
Deferred costs	422		422		474
Unrealized rents & receivable	697		697		446
Secured notes payable	29,279		29,279		29,246
Other liabilities	229		229		120
Capital - FRP	5,009		5,009		6,000
Capital - Third parties	13,786		13,786		14,003
Total liabilities and capital	48,303		48,303		49,369
Amber Ridge
Total Investment	9,970		9,970		509
Total Assets of the Partnership	9,970		9,970		509
Profit (Loss) of the Partnership			0		0
Company's share of Net Loss of the Partnership			0		0
Investments in real estate, net	9,970		9,970		509
Cash and cash equivalents	0		0		0
Deferred costs	0		0		0
Unrealized rents & receivable	0		0		0
Secured notes payable	0		0		0
Other liabilities	0		0		0
Capital - FRP	9,970		9,970		509
Capital - Third parties	0		0		0
Total liabilities and capital	$ 9,970		$ 9,970		$ 509
1800 Half Street
Ownership percent	61.37%		61.37%		59.73%
Total Investment	$ 37,748		$ 37,748		$ 37,314
Total Assets of the Partnership	52,933		52,933		40,161
Profit (Loss) of the Partnership			147		0
Company's share of Net Loss of the Partnership			141		0
Investments in real estate, net	32,358		32,358		14,391
Cash and cash equivalents	17,765		17,765		25,770
Deferred costs	2,810		2,810		0
Unrealized rents & receivable	0		0		0
Secured notes payable	0		0		0
Other liabilities	2,969		2,969		1,363
Capital - FRP	37,481		37,481		37,314
Capital - Third parties	12,483		12,483		1,484
Total liabilities and capital	$ 52,933		$ 52,933		$ 40,161
Woodfield Partnerships
Ownership percent	40.00%		40.00%		40.00%
Total Investment	$ 16,093		$ 16,093		$ 15,919
Total Assets of the Partnership	44,896		44,896		19,214
Profit (Loss) of the Partnership			176		0
Company's share of Net Loss of the Partnership			88		0
Investments in real estate, net	32,768		32,768		1,889
Cash and cash equivalents	11,754		11,754		17,325
Deferred costs	374		374		0
Unrealized rents & receivable	0		0		0
Secured notes payable	0		0		0
Other liabilities	4,996		4,996		1,889
Capital - FRP	15,960		15,960		15,919
Capital - Third parties	23,940		23,940		1,406
Total liabilities and capital	44,896		44,896		19,214
Apartment Mixed Use Totals
Total Assets of the Partnership	409,059		409,059		293,456
Investments in real estate, net	371,582		371,582		246,389
Cash and cash equivalents	32,729		32,729		45,876
Deferred costs	3,860		3,860		505
Unrealized rents & receivable	888		888		686
Secured notes payable	150,153		150,153		69,470
Other liabilities	31,077		31,077		27,326
Capital - FRP	152,527		152,527		153,996
Capital - Third parties	75,302		75,302		42,664
Total liabilities and capital	$ 409,059		$ 409,059		$ 293,456