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Employee Benefit Plans (Bank Owned Life Insurance) (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Bank owned life insurance [Line Items]
Bank-owned life insurance	$ 55,536	$ 54,018
Bank owned life insurance death benefits	133,700	133,800
Insured executive officers with deferred compensation plans
Bank owned life insurance [Line Items]
Bank-owned life insurance	3,100	2,900
Bank owned life insurance death benefits	6,200	6,100
Other insured individuals
Bank owned life insurance [Line Items]
Bank-owned life insurance	$ 52,400	$ 51,000

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- Definition

Bank Owned Life Insurance Death Benefits

+ References

No definition available.

+ Details

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Namespace Prefix:	fbiz_
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Balance Type:	debit
Period Type:	instant

X

- Definition

[Line Items] for Bank owned life insurance [Table]

+ References

No definition available.

+ Details

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Namespace Prefix:	fbiz_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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- Definition

The carrying amount of a life insurance policy on an officer, executive or employee for which the reporting entity (a bank) is entitled to proceeds from the policy upon death of the insured or surrender of the insurance policy.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(10))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

+ Details

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X

- Details

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Namespace Prefix:
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X

- Details

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