Joint Ventures - Unconsolidated JV - Sea Sound Apartments JV (Details) $ in Thousands	1 Months Ended	3 Months Ended		12 Months Ended
	Jan. 31, 2020 USD ($)	Mar. 31, 2021 USD ($) item	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Investments
Net income		$ 2,957	$ (1,335)
Outstanding debt		172,309		$ 161,418
Summarized financial information
Investment in real estate		569,201		551,653
Cash and cash equivalents		52,313	106,427	106,794
Other assets		62,315		63,243
Total assets		1,053,393		1,037,324
Debt, net		169,730		158,915
Other liabilities		76,930		72,035
Equity		568,104	520,910	568,170	$ 529,670
Total liabilities and equity		1,053,393		1,037,324
Total expenses		35,766	19,899
Net income (loss)		$ 2,957	$ (1,335)
Sea Sound Apartments JV
Investments
Value of land contributed	$ 5,100
Mitigation bank credits contributed				400
Cash contributed				4,900
Cash contributed by JV partner				$ 6,900
Ownership percentage		60.00%		60.00%
Unconsolidated joint ventures
Investments
Outstanding debt		$ 44,126		$ 33,088
Sea Sound Apartments JV
Investments
Net income		(3)
Outstanding debt		15,648		8,789
Summarized financial information
Investment in real estate		38,339		29,085
Cash and cash equivalents		14		15
Other assets		20
Total assets		38,373		29,100
Debt, net		15,286		8,378
Other liabilities		5,807		3,439
Equity		17,280		17,283
Total liabilities and equity		38,373		29,100
Total expenses		3
Net income (loss)		(3)
Sea Sound Apartments JV | Sea Sound Apartments JV Loan
Investments
Loan amount	$ 40,300
Outstanding debt		$ 15,600		$ 8,800
Sea Sound Apartments JV | LIBOR | Sea Sound Apartments JV Loan
Investments
Basis spread on variable rate (as a percent)	2.15%
Sea Sound Apartments JV | Apartment
Investments
Number of units to be developed | item		300