Note 7 - Notes Payable - Mortgages and Mezzanine Note Payable (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Debt, gross		$ 1,009,431	$ 925,613
Total debt, net of unamortized debt issuance costs		$ 997,903	913,564
Mortgages and Mezzanine Notes 1[Member] | Flatbush Gardens, Brooklyn, NY [Member]
Maturity date	[1]	Mar. 01, 2028
Interest rate	[1]	3.50%
Debt, gross	[1]	$ 246,000	246,000
Interest rate	[1]	3.50%
Mortgages and Mezzanine Notes 1[Member] | 250 Livingston Street in Brooklyn [Member]
Maturity date	[2]	Dec. 09, 2020
Debt, gross	[2]		75,000
Mortgages and Mezzanine Notes 1[Member] | 250 Livingston Street in Brooklyn [Member] | London Interbank Offered Rate (LIBOR) [Member]
Interest rate	[2]	2.15%
Mortgages and Mezzanine Notes 1[Member] | 141 Livingston Street, Brooklyn [Member]
Maturity date	[3]	Jun. 01, 2028
Interest rate	[3]	3.875%
Debt, gross	[3]	$ 75,817	77,333
Interest rate	[3]	3.875%
Mortgages and Mezzanine Notes 1[Member] | Tribeca House Properties [Member]
Maturity date	[4]	Mar. 06, 2028
Interest rate	[4]	4.506%
Debt, gross	[4]	$ 360,000	360,000
Interest rate	[4]	4.506%
Mortgages and Mezzanine Notes 1[Member] | Aspen [Member]
Maturity date	[5]	Jul. 01, 2028
Interest rate	[5]	3.68%
Debt, gross	[5]	$ 66,862	68,199
Interest rate	[5]	3.68%
Mortgages and Mezzanine Notes 1[Member] | Clover House [Member]
Maturity date	[6]	May 09, 2020
Debt, gross	[6]		64,731
Mortgages and Mezzanine Notes 1[Member] | Clover House [Member] | London Interbank Offered Rate (LIBOR) [Member]
Interest rate	[6]	3.85%
Interest rate	[6]	3.85%
Mortgages and Mezzanine Notes 1[Member] | Property at 10 W 65th St. Manhattan, NY [Member]
Maturity date	[7]	Nov. 01, 2027
Interest rate	[7]	3.375%
Debt, gross	[7]	$ 34,295	34,350
Interest rate	[7]	3.375%
Mortgages and Mezzanine Notes 1[Member] | Residential Property At 1010 Pacific Street [Member]
Maturity date	[8]	Dec. 24, 2020
Interest rate	[8]	3.60%
Debt, gross	[8]	$ 19,457
Interest rate	[8]	3.60%
Mortgages and Mezzanine Notes 2 [Member] | 250 Livingston Street in Brooklyn [Member]
Maturity date	[2]	Jun. 06, 2029
Interest rate	[2]	3.63%
Debt, gross	[2]	$ 125,000
Interest rate	[2]	3.63%
Mortgages and Mezzanine Notes 2 [Member] | Clover House [Member]
Maturity date		Dec. 01, 2029
Interest rate		3.53%
Debt, gross		$ 82,000
Interest rate		3.53%
Mortgages and Mezzanine Notes [Member]
Unamortized debt issuance costs		$ (11,528)	$ (12,049)

[1] The $246,000 mortgage note agreement with New York Community Bank (“NYCB”), entered into on February 21, 2018, matures on March 1, 2028, and bears interest at 3.5% through February 2023 and thereafter at the prime rate plus 2.75%, with an option to fix the rate subject to the payment of a fee that fluctuates depending on the date the election is made. The note requires interest-only payments through August 2020, and monthly principal and interest payments thereafter based on a 30-year amortization schedule. The Company has the option to prepay all (but not less than all) of the unpaid balance of the note prior to the maturity date, subject to certain prepayment premiums, as defined.

[2] On May 31, 2019, the Company repaid the debt secured by the 250 Livingston Street property that was scheduled to mature in 2020, from the proceeds of a $125,000 first mortgage loan with Citi Real Estate Funding Inc. The loan matures on June 6, 2029, bears interest at 3.63% and requires interest-only payments for the entire term. The Company has the option to prepay all (but not less than all) of the unpaid balance of the note within three months of maturity, without a prepayment premium.

[3] The $79,500 mortgage note agreement with NYCB matures on June 1, 2028, and bears interest at 3.875%. The note required interest-only payments through June 2017, and monthly principal and interest payments of $374 thereafter based on a 30-year amortization schedule.

[4] The $360,000 loan with Deutsche Bank, entered into on February 21, 2018, matures on March 6, 2028, bears interest at 4.506% and requires interest-only payments for the entire term. The Company has the option to prepay all (but not less than all) of the unpaid balance of the loan prior to the maturity date, subject to a prepayment premium if it occurs prior to December 6, 2027.

[5] The $70,000 mortgage note agreement with Capital One Multifamily Finance LLC matures on July 1, 2028, and bears interest at 3.68%. The note required interest-only payments through July 2017, and monthly principal and interest payments of $321 thereafter based on a 30-year amortization schedule. The Company has the option to prepay the note prior to the maturity date, subject to a prepayment premium.

[6] On November 8, 2019, the Company repaid the debt secured by the Clover House property that was scheduled to mature in 2020, from the proceeds of a $82,000 first mortgage loan with MetLife Investment Management. The loan matures on December 1, 2029, bears interest at 3.53% and requires interest-only payments for the entire term. The Company has the option, commencing on January 1, 2024, to prepay the note prior to the maturity date, subject to a prepayment premium if it occurs prior to September 2, 2029.

[7] On October 27, 2017, the Company entered into a $34,350 mortgage note agreement with NYCB, related to the 10 West 65th Street acquisition. The note matures on November 1, 2027, and bears interest at 3.375% for the first five years and thereafter at the prime rate plus 2.75%, subject to an option to fix the rate. The note required interest-only payments through October 2019, and monthly principal and interest payments of $152 thereafter based on a 30-year amortization schedule. The Company has the option to prepay all (but not less than all) of the unpaid balance of the note prior to the maturity date, subject to certain prepayment premiums, as defined.

[8] On December 24, 2019, the Company entered into a $18,600 mortgage note agreement with CIT Bank, N.A., related to the 1010 Pacific Street acquisition. The Company also entered into a construction loan secured by the building with the same lender that will provide up to $2,987 for eligible pre-development and carrying costs, of which $857 was drawn as of December 31, 2019. The notes mature on December 24, 2020, are subject to a one-year extension option, require interest-only payments and bear interest at one-month LIBOR plus 3.60% (5.4% as of December 31, 2019).