Segment Information (Details)	12 Months Ended
	Dec. 31, 2021 USD ($) segment	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of Operating Segments | segment	4
Assets	$ 3,563,368,000	$ 4,281,079,000
capitalized expenditures for long lived assets	27,654,000	49,426,000	$ 43,185,000
Operating Leases, Income Statement, Lease Revenue	404,581,000	445,815,000	406,916,000
adjusted funds from operations	305,984,000	340,007,000	317,828,000
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest	20,532,000	(181,603,000)	(7,458,000)
Interest Expense	102,414,000	118,558,000	111,964,000
Depreciation	139,951,000	163,876,000	149,884,000
Share-based Compensation	(3,289,000)	(1,644,000)	(1,223,000)
Gain (Loss) on Condemnation	12,000	(517,000)	(954,000)
Gains (Losses) on Sales of Investment Real Estate	(21,109,000)	(23,456,000)	(1,567,000)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	0	0	(1,831,000)
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions	665,000	314,000	0
Gain (Loss) on Extinguishment of Debt	0	6,674,000	84,000
Management fees net of deferrals	0	1,963,000	21,752,000
noncash loan interest income	970,000	180,116,000	2,987,000
Allowance for Loan and Lease Losses, Loans Acquired	874,000	6,103,000	2,038,000
rental and other property revenues	405,562,000	450,389,000	410,677,000
interest revenues loans and notes	45,496,000	50,723,000	59,750,000
miscellaneous revenues	84,000	73,000	0
Revenues	451,142,000	501,185,000	470,427,000
Contract with Customer, Liability, Revenue Recognized	5,660,000	5,059,000	6,274,000
Residential Properties
Segment Reporting Information [Line Items]
capitalized expenditures for long lived assets	14,296,000	14,311,000	14,511,000
adjusted funds from operations	127,273,000	132,858,000	122,753,000
Interest Expense	55,346,000	60,676,000	62,455,000
Multifamily Communities
Segment Reporting Information [Line Items]
Assets	1,958,592,000	1,745,020,000
Operating Leases, Income Statement, Lease Revenue	217,013,000	234,038,000	220,872,000
Depreciation	89,355,000	101,823,000	99,384,000
financingsegment [Member]
Segment Reporting Information [Line Items]
Assets	226,734,000	321,026,000
adjusted funds from operations	45,479,000	50,689,000	59,750,000
Interest Expense	2,427,000	4,564,000	2,074,000
New Market Properties [Member]
Segment Reporting Information [Line Items]
Assets	1,032,658,000	1,072,090,000
capitalized expenditures for long lived assets	8,286,000	9,494,000	8,913,000
Operating Leases, Income Statement, Lease Revenue	108,102,000	107,525,000	96,389,000
adjusted funds from operations	75,326,000	77,091,000	68,815,000
Interest Expense	25,654,000	26,379,000	24,566,000
Depreciation	45,753,000	51,813,000	44,786,000
All Other Segments [Member]
Segment Reporting Information [Line Items]
Assets	17,836,000	20,951,000
adjusted funds from operations	29,144,000	28,534,000	4,525,000
Preferred Office Properties [Member]
Segment Reporting Information [Line Items]
Assets	327,548,000	1,121,992,000
capitalized expenditures for long lived assets	5,072,000	25,621,000	19,761,000
Operating Leases, Income Statement, Lease Revenue	80,447,000	108,826,000	93,416,000
adjusted funds from operations	57,822,000	79,296,000	66,510,000
Interest Expense	18,987,000	26,939,000	22,869,000
Depreciation	33,864,000	47,829,000	40,888,000
Contract with Customer, Liability				$ 36,000,000.0
Contract with Customer, Liability, Revenue Recognized	3,800,000	2,800,000	2,700,000
Miscellaneous
Segment Reporting Information [Line Items]
adjusted funds from operations	84,000	73,000	0
corporate entities
Segment Reporting Information [Line Items]
Depreciation	$ 221,000	$ 212,000	$ 7,000