Note 7 - Notes Payable - Mortgages and Mezzanine Note Payable (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Debt, gross		$ 925,613	$ 855,116
Unamortized debt issuance costs		(12,049)	(11,170)
Total debt, net of unamortized debt issuance costs		$ 913,564	843,946
Mortgages and Mezzanine Notes 1[Member] | Flatbush Gardens, Brooklyn, NY [Member]
Maturity date	[1]	Oct. 01, 2024
Interest rate	[1]	3.88%
Debt, gross	[1]		148,438
Mortgages and Mezzanine Notes 1[Member] | 250 Livingston Street in Brooklyn [Member]
Maturity date	[2]	May 06, 2023
Interest rate	[2]	4.00%
Debt, gross	[2]		34,294
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]	$ 77,333	78,792
Mortgages and Mezzanine Notes 1[Member] | Tribeca House Properties [Member]
Maturity date	[4]	Nov. 09, 2018
Debt, gross	[4]		410,000
Mortgages and Mezzanine Notes 1[Member] | Tribeca House Properties [Member] | London Interbank Offered Rate (LIBOR) [Member]
Interest rate	[4]	3.75%
Mortgages and Mezzanine Notes 1[Member] | Aspen [Member]
Maturity date	[5]	Jul. 01, 2028
Interest rate	[5]	3.68%
Debt, gross	[5]	$ 68,199	69,383
Mortgages and Mezzanine Notes 1[Member] | 107 Columbia Heights in Brooklyn, NY [Member]
Maturity date	[6]	May 09, 2020
Debt, gross	[6]	$ 64,731	60,067
Mortgages and Mezzanine Notes 1[Member] | 107 Columbia Heights in Brooklyn, NY [Member] | London Interbank Offered Rate (LIBOR) [Member]
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]	$ 34,350	34,350
Mortgages and Mezzanine Notes 2[Member] | Flatbush Gardens, Brooklyn, NY [Member]
Maturity date	[1]	Oct. 01, 2024
Interest rate	[1]	3.88%
Debt, gross	[1]		19,792
Mortgages and Mezzanine Notes 2[Member] | 250 Livingston Street in Brooklyn [Member]
Maturity date	[2]	Dec. 09, 2020
Debt, gross	[2]	$ 75,000
Interest rate	[2]	2.15%
Mortgages and Mezzanine Notes 2[Member] | Tribeca House Properties [Member]
Maturity date	[4]	Mar. 06, 2028
Interest rate	[4]	4.506%
Debt, gross	[4]	$ 360,000
Mortgages and Mezzanine Notes 3[Member] | Flatbush Gardens, Brooklyn, NY [Member]
Maturity date	[1]	Mar. 01, 2028
Interest rate	[1]	3.50%
Debt, gross	[1]	$ 246,000
Mortgages and Mezzanine Notes [Member]
Unamortized debt issuance costs		$ (12,049)	$ (11,170)

[1] On February 21, 2018, the Company repaid the debt secured by the Flatbush Gardens property that was scheduled to mature in 2024, from the proceeds of a $246,000 first mortgage loan with New York Community Bank ("NYCB"). The loan matures on March 1, 2028, and bears interest at 3.5% for the first five years and thereafter at the prime rate plus 2.75%, subject to an option to fix the rate. The loan requires interest-only payments through August 2020, and monthly principal and interest payments thereafter based on a 30-year amortization schedule.

[2] On December 6, 2018, the Company defeased the debt secured by the 250 Livingston Street property that was scheduled to mature in 2023, from the proceeds of a $75,000 first mortgage loan with Citibank, N.A.. The loan matures on December 9, 2020, is subject to three one-year extension options, requires interest-only payments and bears interest at one-month LIBOR plus 2.15% (4.7% as of December 31, 2018).

[3] The NYCB loan 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] On February 21, 2018, the Company repaid the $410,000 loan package secured by the Tribeca House property with the proceeds of a $360,000 loan with Deutsche Bank and cash on hand. The loan matures on March 6, 2028, bears interest at 4.506% and requires interest-only payments for the entire term.

[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.

[6] On May 9, 2017, the Company entered into a $59,000 mortgage note agreement with a unit of Blackstone Mortgage Trust, Inc., related to the 107 Columbia Heights acquisition. The Company also entered into a construction loan secured by the building with the same lender that will provide up to $14,700 for eligible capital improvements and carrying costs, of which $5,731 was drawn as of December 31, 2018. The notes mature on May 9, 2020, are subject to two one-year extension options, require interest-only payments and bear interest at one-month LIBOR plus 3.85% (6.4% as of December 31, 2018).

[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 requires interest-only payments through October 2019, and monthly principal and interest payments thereafter based on a 30-year amortization schedule.