Investments in Joint Ventures (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Mar. 31, 2016	Jun. 30, 2013	Oct. 04, 2006
Company's share of Net Loss of the Partnership	$ (13)	$ (12)		$ (36)	$ (1,589)
Revenue - Reimbursements	200	170		548	469
Total revenues	5,742	5,035		16,370	10,389
Operating expenses	983	875		2,951	1,312
Property taxes	663	647		1,949	1,384
Total cost of operations	4,074	5,294		15,061	9,471
Total operating profit	1,668	(259)		1,309	918
Interest expense	$ (768)	$ (783)		$ (2,418)	$ (783)
Brooksville Quarry, LLC
Ownership percent	50.00%			50.00%		50.00%			50.00%
Total Investment	$ 7,477			$ 7,477		$ 7,516
Total Assets of the Partnership	$ 14,404			14,404		14,411
Net Loss of the Partnership				(70)		(80)
Company's share of Net Loss of the Partnership				$ (35)		$ (40)
BC FRP Realty, LLC
Ownership percent	50.00%			50.00%		50.00%	50.00%
Total Investment	$ 5,966			$ 5,966		$ 5,890
Total Assets of the Partnership	$ 20,689			20,689		15,027
Net Loss of the Partnership				0		0
Company's share of Net Loss of the Partnership				$ 0		$ 0
RiverFront Holdings II, LLC
Ownership percent	80.00%			80.00%
Total Investment	$ 11,646			$ 11,646
Total Assets of the Partnership	20,793			20,793
Net Loss of the Partnership				(1)
Company's share of Net Loss of the Partnership				(1)
Riverfront Holdings I, LLC
Ownership percent						0.00%		77.14%
Total Investment			$ 8,583			$ 0
Total Assets of the Partnership						0
Net Loss of the Partnership						(2,019)
Company's share of Net Loss of the Partnership						(1,558)
Rental revenue			3,053
Revenue - Reimbursements			33
Total revenues			3,086
Depreciation and amortization			1,958
Operating expenses			1,096
Property taxes			459
Total cost of operations			3,513
Total operating profit			(427)
Interest expense			(1,592)
Net loss of the Partnership			$ (2,019)
Joint Ventures
Total Investment	25,089			25,089		13,406
Total Assets of the Partnership	$ 55,886			55,886		29,438
Net Loss of the Partnership				(71)		(2,099)
Company's share of Net Loss of the Partnership				$ (36)		$ (1,598)