Investment in Unconsolidated Ventures - Balance Sheet Information (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
ASSETS
Real estate properties, net of accumulated depreciation of $144,299 and $145,600	$ 224,620	$ 160,192
Cash and cash equivalents	29,598	19,885	$ 15,650
Other assets	7,792	7,390
Total Assets	398,048	365,741
Liabilities:
Mortgages payable, net of deferred costs of $3,954 and $5,537	134,193	130,434
Accounts payable and accrued liabilities	20,464	20,536
Total Liabilities	191,755	188,053
Commitments and contingencies
Equity:
Total unconsolidated joint venture equity	206,272	177,772
Total Liabilities and Equity	398,048	365,741
Deferred mortgage costs	787	880
Mortgages payable
Equity:
Deferred mortgage costs	485	563
Unconsolidated Joint Ventures
ASSETS
Real estate properties, net of accumulated depreciation of $144,299 and $145,600	824,624	1,075,178
Cash and cash equivalents	13,328	16,939
Other assets	34,415	29,392
Total Assets	872,367	1,121,509
Liabilities:
Mortgages payable, net of deferred costs of $3,954 and $5,537	659,148	829,646
Accounts payable and accrued liabilities	21,046	20,237
Total Liabilities	680,194	849,883
Commitments and contingencies
Equity:
Total unconsolidated joint venture equity	192,173	271,626
Total Liabilities and Equity	872,367	1,121,509
BRT's interest in joint venture equity	128,478	169,474
Real estate properties, net of accumulated depreciation	144,299	145,600
Unconsolidated Joint Ventures | Mortgages payable
Equity:
Deferred mortgage costs	$ 3,954	$ 5,537