Note 4 - Real Estate Under Development (Details Textual)	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Real Estate Under Development, Capitalized Costs of Interest, Real Estate Taxes, Insurance, Legal Costs and Payroll	$ 21,300,000	$ 24,900,000
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Cost of Investment in Real Estate Sold	190,859,948	767,246,512	$ 315,954,464
Total Net Gain Loss on Sale of Operating Properties	79,218,000	229,840,000	$ 93,538,000
Real Estate Investment Property, Net, Total	9,209,053,000	9,250,519,000
Impairment of Real Estate	48,700,000	79,200,000
Real Estate Inventory, Capitalized Interest Costs Incurred	9,400,000	13,900,000
Real Estate Development Projects, Real Estate Taxes and Insurance Capitalized	1,300,000	2,600,000
Real Estate Development Projects, Payroll Costs Capitalized	1,200,000	$ 1,900,000
Dania Pointe [Member]
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Cost of Investment in Real Estate Sold	32,500,000
Total Net Gain Loss on Sale of Operating Properties	4,300,000
Mill Station [Member]
Real Estate Investment Property, Net, Total	80,500,000
Real Estate Inventory, Capitalized Interest Costs, Ending Balance	9,200,000
Promenade at Christiana [Member]
Impairment of Real Estate	$ 11,500,000
Real Estate Under Development [Member]
Number of Real Estate Properties	2,018