Investments in Joint Ventures (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Jul. 31, 2019	Dec. 24, 2018	Sep. 30, 2016	Oct. 04, 2006
Total Investment	$ 103,822		$ 103,822		$ 88,884
Total Assets of the Partnership	258,989		258,989		152,700
Profit (Loss) of the Partnership			(1,888)		(149)
Company's share of Net Loss of the Partnership	(746)	$ (13)	(1,282)	$ (36)	(88)
Investments in real estate, net	243,182		243,182		116,859
Cash and cash equivalents	9,119		9,119		35,777
Deferred costs	6,584		6,584		64
Unrealized rents & receivable	104		104		0
Secured notes payable	68,966		68,966		9,549
Other liabilities	21,535		21,535		4,930
Capital - FRP	114,167		114,167		100,282
Capital - Third parties	54,321		54,321		37,939
Total liabilities and capital	$ 258,989		$ 258,989		$ 152,700
Brooksville Quarry, LLC
Ownership percent	50.00%		50.00%		50.00%				50.00%
Total Investment	$ 7,464		$ 7,464		$ 7,449
Total Assets of the Partnership	14,383		14,383		14,325
Profit (Loss) of the Partnership			(68)		(122)
Company's share of Net Loss of the Partnership			(34)		(61)
Investments in real estate, net	14,294		14,294		14,299
Cash and cash equivalents	89		89		20
Deferred costs	0		0		6
Unrealized rents & receivable	0		0		0
Secured notes payable	0		0		0
Other liabilities	141		141		119
Capital - FRP	7,465		7,465		7,449
Capital - Third parties	6,777		6,777		6,757
Total liabilities and capital	$ 14,383		$ 14,383		$ 14,325
BC FRP Realty, LLC
Ownership percent	50.00%		50.00%		50.00%			50.00%
Total Investment	$ 5,487		$ 5,487		$ 5,976
Total Assets of the Partnership	22,857		22,857		21,371
Profit (Loss) of the Partnership			(990)		0
Company's share of Net Loss of the Partnership			(495)		0
Investments in real estate, net	22,532		22,532		21,352
Cash and cash equivalents	18		18		11
Deferred costs	255		255		8
Unrealized rents & receivable	52		52		0
Secured notes payable	11,920		11,920		9,549
Other liabilities	75		75		38
Capital - FRP	5,431		5,431		5,892
Capital - Third parties	5,431		5,431		5,892
Total liabilities and capital	$ 22,857		$ 22,857		$ 21,371
RiverFront Holdings II, LLC
Ownership percent	80.00%		80.00%		80.00%
Total Investment	$ 25,726		$ 25,726		$ 19,865
Total Assets of the Partnership	78,282		78,282		38,869
Profit (Loss) of the Partnership			(602)		(66)
Company's share of Net Loss of the Partnership			(597)		(66)
Investments in real estate, net	77,713		77,713		38,793
Cash and cash equivalents	569		569		76
Deferred costs	0		0		0
Unrealized rents & receivable	0		0		0
Secured notes payable	27,671		27,671		0
Other liabilities	7,903		7,903		1,887
Capital - FRP	37,077		37,077		31,347
Capital - Third parties	5,631		5,631		5,635
Total liabilities and capital	$ 78,282		$ 78,282		$ 38,869
Bryant Street Partnerships
Ownership percent	61.36%		61.36%		61.36%		61.36%
Total Investment	$ 57,827		$ 57,827		$ 55,000
Total Assets of the Partnership	90,441		90,441		77,541
Profit (Loss) of the Partnership			(130)		0
Company's share of Net Loss of the Partnership			(130)		0
Investments in real estate, net	78,176		78,176		41,821
Cash and cash equivalents	5,884		5,884		35,670
Deferred costs	6,329		6,329		50
Unrealized rents & receivable	52		52		0
Secured notes payable	0		0		0
Other liabilities	13,416		13,416		2,886
Capital - FRP	56,876		56,876		55,000
Capital - Third parties	20,149		20,149		19,655
Total liabilities and capital	90,441		90,441		77,541
Hyde Park
Total Investment	1,067		1,067		594
Total Assets of the Partnership	$ 1,067		1,067		594
Profit (Loss) of the Partnership			0		39
Company's share of Net Loss of the Partnership			$ 0		39
Investments in real estate, net					594
Cash and cash equivalents					0
Deferred costs					0
Unrealized rents & receivable					0
Secured notes payable					0
Other liabilities					0
Capital - FRP					594
Capital - Third parties					0
Total liabilities and capital					$ 594
DST Hickory Creek
Ownership percent	26.65%		26.65%			26.65%
Total Investment	$ 5,934		$ 5,934
Total Assets of the Partnership	51,642		51,642
Profit (Loss) of the Partnership			(98)
Company's share of Net Loss of the Partnership			(26)
Amber Ridge
Total Investment	317		317
Total Assets of the Partnership	317		317
Profit (Loss) of the Partnership			0
Company's share of Net Loss of the Partnership			0
Others
Investments in real estate, net	50,467		50,467
Cash and cash equivalents	2,559		2,559
Deferred costs	0		0
Unrealized rents & receivable	0		0
Secured notes payable	29,375		29,375
Other liabilities	0		0
Capital - FRP	7,318		7,318
Capital - Third parties	16,333		16,333
Total liabilities and capital	$ 53,026		$ 53,026