Sharebased Compensation Arrangement By Share based Payment Award Performance Period

No definition available.

Name:	func_SharebasedCompensationArrangementByShareBasedPaymentAwardPerformancePeriod
Namespace Prefix:	func_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Sharebased Compensation Arrangement By Share Based Payment Award Vesting Period

+ References

No definition available.

+ Details

Name:	func_SharebasedCompensationArrangementByShareBasedPaymentAwardVestingPeriod
Namespace Prefix:	func_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Sharebased Compensation Percentage Of Award Based On Performance

+ References

No definition available.

+ Details

Name:	func_SharebasedCompensationPercentageOfAwardBasedOnPerformance
Namespace Prefix:	func_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479830/718-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_AllocatedShareBasedCompensationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of commitment made to pay deferred cash remuneration.

+ References

No definition available.

+ Details

Name:	us-gaap_DeferredCompensationArrangementWithIndividualCashAwardGrantedAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The maximum number of shares authorized for issuance under the deferred compensation arrangement as of the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_DeferredCompensationArrangementWithIndividualSharesAuthorizedForIssuance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of shares issued pursuant to the terms of a deferred compensation arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (l)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_DeferredCompensationArrangementWithIndividualSharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(03)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(01)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(01)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of shares issued under share-based payment arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	srt_TitleOfIndividualAxis=srt_DirectorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_TitleOfIndividualAxis=func_EmployeesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=func_TwentyEighteenEquityPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=func_Year2022Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=func_LongTermIncentivePlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=func_Year2021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=func_Year2023Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=func_Year2024Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=func_PerformanceVestedSharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_TitleOfIndividualAxis=srt_OfficerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=func_TimeVestedSharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Equity Compensation Plan Information (Details) - USD ($)										1 Months Ended						3 Months Ended
	Mar. 15, 2025	Mar. 09, 2025	May 05, 2024	Mar. 15, 2024	Mar. 09, 2024	May 05, 2023	Mar. 09, 2023	May 05, 2022	Mar. 26, 2020	Feb. 28, 2025	May 31, 2024	Mar. 31, 2023	May 31, 2022	Mar. 31, 2022	May 31, 2021	Mar. 31, 2025	Mar. 31, 2024
Director [Member]
Amount payable to non-employee directors																$ 15,000
Fully-vested shares of common stock issued																1,000
Employees [Member]
Stock compensation expense																$ 15,567,000	$ 5,058,000
2018 Equity Plan \| Maximum [Member]
Maximum issuance of common stock options																325,000
2018 Equity Plan \| Director [Member]
Fully-vested shares of common stock issued											14,325
Fully vested shares of common stock issued, per share value											$ 21.94
Stock compensation expense																$ 78,573,000	61,937,000
Restricted Stock Units (RSUs)
Shares of common stock grant date fair market value										$ 37.59
Stock compensation expense																11,287,000
Unrecognized compensation expense related to unvested units																395,036,000
Restricted Stock Units (RSUs) \| Year 2022 [Member]
Stock compensation expense																11,379,000	26,145,000
Restricted Stock Units (RSUs) \| Long-Term Incentive Plan [Member]
Shares of common stock grant date fair market value														$ 21.88	$ 17.93
Restricted Stock Units (RSUs) \| Long-Term Incentive Plan [Member] \| Year 2021 [Member]
Stock compensation expense																	16,571,000
Restricted Stock Units (RSUs) \| Long-Term Incentive Plan [Member] \| Year 2023 [Member]
Shares of common stock grant date fair market value												$ 18.25
Stock compensation expense																27,585,000	$ 27,585,000
Unrecognized compensation expense related to unvested units																110,340,000
Restricted Stock Units (RSUs) \| Long-Term Incentive Plan [Member] \| Year 2024 [Member]
Shares of common stock grant date fair market value											$ 22.26
Stock compensation expense																28,314,000
Unrecognized compensation expense related to unvested units																$ 245,388,000
Performance Vesting Restricted Shares
Share based compensation performance period										3 years
Share-based compensation shares of common stock granted										6,006
Performance Vesting Restricted Shares \| Officer [Member] \| Share-based Payment Arrangement, Tranche One
Share-based compensation performance based award, percent																50.00%
Performance Vesting Restricted Shares \| Officer [Member] \| Share-based Payment Arrangement, Tranche Two
Share-based compensation performance based award, percent																150.00%
Performance Vesting Restricted Shares \| Long-Term Incentive Plan [Member]
Share based compensation performance period													3 years		3 years
Share-based compensation award vesting period									3 years
Share-based compensation shares of common stock granted														8,096	7,389
Share-based compensation shares failed to vest					7,389
Performance Vesting Restricted Shares \| Long-Term Incentive Plan [Member] \| Year 2023 [Member]
Share-based compensation shares of common stock granted												10,214
Performance Vesting Restricted Shares \| Long-Term Incentive Plan [Member] \| Year 2024 [Member]
Share based compensation performance period											3 years
Share-based compensation shares of common stock granted											8,593
Time-Vesting Restricted Shares
Share-based compensation award vesting period										3 years
Share-based compensation shares of common stock granted										4,797
Time-Vesting Restricted Shares \| Long-Term Incentive Plan [Member]
Share-based compensation award vesting period																3 years
Share-based compensation shares of common stock granted		2,080												6,238	3,693
Shares-based compensation shares of common stock issued			1,233		2,079	1,230	2,079	1,230
Time-Vesting Restricted Shares \| Long-Term Incentive Plan [Member] \| Year 2021 [Member]
Share-based compensation award vesting period															3 years
Time-Vesting Restricted Shares \| Long-Term Incentive Plan [Member] \| Year 2022 [Member]
Share-based compensation award vesting period														3 years
Time-Vesting Restricted Shares \| Long-Term Incentive Plan [Member] \| Year 2023 [Member]
Share-based compensation award vesting period												3 years
Share-based compensation shares of common stock granted	2,639											7,920
Shares-based compensation shares of common stock issued				2,639
Time-Vesting Restricted Shares \| Long-Term Incentive Plan [Member] \| Year 2024 [Member]
Share-based compensation award vesting period											3 years
Share-based compensation shares of common stock granted											6,662