Investment in Unconsolidated Ventures - Balance Sheet Information (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
ASSETS
Real estate properties, net of accumulated depreciation	$ 140,991	$ 160,192
Cash and cash equivalents	34,666	19,885	$ 16,874
Other assets	7,851	7,390
Total Assets	351,239	365,741
Liabilities:
Mortgages payable	114,745	130,434
Accounts payable and accrued liabilities	18,936	20,536
Total Liabilities	170,774	188,053
Commitments and contingencies
Equity:
Total unconsolidated joint venture equity	180,480	177,772
Total Liabilities and Equity	351,239	365,741
Deferred mortgage costs	740	880
Mortgages payable
Equity:
Deferred mortgage costs	433	563
Unconsolidated Joint Ventures
ASSETS
Real estate properties, net of accumulated depreciation	896,944	1,075,178
Cash and cash equivalents	15,249	16,939
Other assets	32,116	29,392
Real estate property held for sale	139,711	0
Total Assets	1,084,020	1,121,509
Liabilities:
Mortgages payable	814,067	829,646
Accounts payable and accrued liabilities	20,108	20,237
Total Liabilities	834,175	849,883
Equity:
Total unconsolidated joint venture equity	249,845	271,626
Total Liabilities and Equity	1,084,020	1,121,509
BRT's interest in joint venture equity	159,799	169,474
Real estate properties, net of accumulated depreciation	142,413	145,600
Unconsolidated Joint Ventures | Mortgages payable
Equity:
Deferred mortgage costs	$ 4,951	$ 5,537