Deposit (Schedule of deposit liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Non-interest bearing deposits	$ 429,691	$ 506,613
Non-Interest bearing deposits, percentage	27.00%	32.00%
Interest bearing deposits	$ 1,145,378	$ 1,064,120
Total deposits	$ 1,575,069	$ 1,570,733
Non-Interest and Interest bearing deposits, percentage	100.00%	100.00%
Demand Deposit Liability [Member]
Interest bearing deposits	$ 381,782	$ 327,685
Interest bearing deposits, percentage	24.00%	21.00%
Money Market Liability [Member]
Interest bearing deposits	$ 338,153	$ 365,192
Interest bearing deposits, percentage	22.00%	23.00%
Savings Deposit Liability [Member]
Interest bearing deposits	$ 204,389	$ 250,720
Interest bearing deposits, percentage	13.00%	16.00%
Time Deposit Retail Liability [Member]
Interest bearing deposits	$ 160,380	$ 120,523
Interest bearing deposits, percentage	10.00%	8.00%
Time Deposit Brokered Liability [Member]
Interest bearing deposits	$ 60,674
Interest bearing deposits, percentage	4.00%	0.00%

Percentage of aggregate liabilities related to interest bearing deposits.

No definition available.

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- Definition

Percentage of aggregate liabilities related to non-interest and interest bearing deposits.

+ References

No definition available.

+ Details

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- Definition

Percentage of aggregate liabilities related to non interest bearing deposits.

+ References

No definition available.

+ Details

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Namespace Prefix:	func_
Data Type:	dtr-types:percentItemType
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- Definition

The aggregate of all domestic interest-bearing and noninterest-bearing deposit liabilities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.12)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

+ Details

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- Definition

Total amount of interest-bearing domestic deposit liabilities, which may include brokered, retail, demand, checking, notice of withdrawal, money market and other interest-bearing deposits.

+ References

+ Details

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- Definition

Amount of domestic noninterest-bearing deposits held by the entity, which may include demand deposits, checking, brokered and retail deposits.

+ References

+ Details

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- Details

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- Details

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- Details

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- Details

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- Details

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