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Related Parties (Schedule Of Related Party Expenses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Related Party Transaction, Expenses from Transactions with Related Party	$ 3,006	$ 2,733	$ 2,480
Leasing Agent Fees [Member]
Related Party Transaction, Expenses from Transactions with Related Party	0	154	133
Operation Of Parking Garages [Member]
Related Party Transaction, Expenses from Transactions with Related Party	81	118	95
Building Management Fees [Member]
Related Party Transaction, Expenses from Transactions with Related Party	2,110	2,001	1,935
Property Construction Management Fees [Member]
Related Party Transaction, Expenses from Transactions with Related Party	251	250	136
Tower's project consulting fees
Related Party Transaction, Expenses from Transactions with Related Party	335	0	0
Dividends Paid On Company Stock Held By Tower [Member]
Related Party Transaction, Expenses from Transactions with Related Party	$ 229	$ 210	$ 181

X

- Definition

Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Details

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Namespace Prefix:
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X

- Details

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Balance Type:
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X

- Details

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X

- Details

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X

- Details

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- Details

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