For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Term of lessor's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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Leases - Lessor Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Lessor, Lease, Description [Line Items]
Revenues	$ 199,142	$ 226,350	$ 232,825
Minimum
Lessor, Lease, Description [Line Items]
Lessor, operating lease, term (years)	5 years
Maximum
Lessor, Lease, Description [Line Items]
Lessor, operating lease, term (years)	25 years
The Alexander apartment tower \| Minimum
Lessor, Lease, Description [Line Items]
Lessor, operating lease, term (years)	1 year
The Alexander apartment tower \| Maximum
Lessor, Lease, Description [Line Items]
Lessor, operating lease, term (years)	2 years
Revenue Benchmark \| Bloomberg \| Customer Concentration Risk
Lessor, Lease, Description [Line Items]
Revenues	$ 109,066	$ 109,113	$ 107,356
Percentage rent contributed by tenant	55.00%	48.00%	46.00%