Investments in Joint Ventures (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Mar. 31, 2016	Oct. 04, 2006
Total Investment	$ 94,294		$ 88,884
Total Assets of the Partnership	173,556		152,700
Net Loss of the Partnership	(448)		(149)
Company's share of Net Loss of the Partnership	(264)	$ (12)	(88)
Investments in real estate, net	142,486		116,859
Cash and cash equivalents	30,888		35,777
Deferred costs	182		64
Secured notes payable	12,585		9,549
Other liabilities	17,483		4,930
Capital - FRP	105,651		100,282
Capital - Third parties	37,837		37,939
Total liabilities and capital	$ 173,556		$ 152,700
Brooksville Quarry, LLC
Ownership percent	50.00%		50.00%		50.00%
Total Investment	$ 7,492		$ 7,449
Total Assets of the Partnership	14,334		14,325
Net Loss of the Partnership	(20)		(122)
Company's share of Net Loss of the Partnership	(10)		(61)
Investments in real estate, net	14,298		14,299
Cash and cash equivalents	32		20
Deferred costs	4		6
Secured notes payable	0		0
Other liabilities	42		119
Capital - FRP	7,492		7,449
Capital - Third parties	6,800		6,757
Total liabilities and capital	$ 14,334		$ 14,325
BC FRP Realty, LLC
Ownership percent	50.00%		50.00%	50.00%
Total Investment	$ 5,812		$ 5,976
Total Assets of the Partnership	21,950		21,371
Net Loss of the Partnership	(340)		0
Company's share of Net Loss of the Partnership	(170)		0
Investments in real estate, net	21,820		21,352
Cash and cash equivalents	2		11
Deferred costs	128		8
Secured notes payable	10,355		9,549
Other liabilities	81		38
Capital - FRP	5,757		5,892
Capital - Third parties	5,757		5,892
Total liabilities and capital	21,950		21,371
Essexshire Loan
Total Investment	755		594
Total Assets of the Partnership	755		594
Net Loss of the Partnership	0		39
Company's share of Net Loss of the Partnership	0		39
Investments in real estate, net	755		594
Cash and cash equivalents	0		0
Deferred costs	0		0
Secured notes payable	0		0
Other liabilities	0		0
Capital - FRP	755		594
Capital - Third parties	0		0
Total liabilities and capital	$ 755		$ 594
RiverFront Holdings II, LLC
Ownership percent	80.00%		80.00%
Total Investment	$ 25,141		$ 19,865
Total Assets of the Partnership	53,499		38,869
Net Loss of the Partnership	(182)		(66)
Company's share of Net Loss of the Partnership	(178)		(66)
Investments in real estate, net	49,733		38,793
Cash and cash equivalents	3,766		76
Deferred costs	0		0
Secured notes payable	2,230		0
Other liabilities	9,085		1,887
Capital - FRP	36,553		31,347
Capital - Third parties	5,631		5,635
Total liabilities and capital	$ 53,499		$ 38,869
Bryant Street Partnerships
Ownership percent	61.36%		61.36%
Total Investment	$ 55,094		$ 55,000
Total Assets of the Partnership	83,018		77,541
Net Loss of the Partnership	94		0
Company's share of Net Loss of the Partnership	94		0
Investments in real estate, net	55,880		41,821
Cash and cash equivalents	27,088		35,670
Deferred costs	50		50
Secured notes payable	0		0
Other liabilities	8,275		2,886
Capital - FRP	55,094		55,000
Capital - Third parties	19,649		19,655
Total liabilities and capital	$ 83,018		$ 77,541