SUMMARY OF INVESTMENTS - Fair Value of Investments (Details) - USD ($)	Sep. 30, 2025	Dec. 31, 2024
AVAILABLE-FOR-SALE
Amortized Cost	$ 2,054,127,000	$ 1,961,531,000
Gross Unrealized Gain	22,012,000	3,640,000
Gross Unrealized Loss	59,773,000	96,840,000
Allowance for Credit Losses	0	0
Fair Value	2,016,366,000	1,868,331,000
US Treasury and government agencies
AVAILABLE-FOR-SALE
Amortized Cost	109,416,000	126,402,000
Gross Unrealized Gain	468,000	153,000
Gross Unrealized Loss	6,252,000	9,255,000
Allowance for Credit Losses	0	0
Fair Value	103,632,000	117,301,000
States, municipalities and political subdivisions
AVAILABLE-FOR-SALE
Amortized Cost	249,977,000	252,936,000
Gross Unrealized Gain	1,653,000	52,000
Gross Unrealized Loss	1,914,000	5,084,000
Allowance for Credit Losses	0	0
Fair Value	249,716,000	247,904,000
Corporate
AVAILABLE-FOR-SALE
Amortized Cost	743,936,000	728,662,000
Gross Unrealized Gain	8,964,000	1,354,000
Gross Unrealized Loss	24,450,000	40,633,000
Allowance for Credit Losses	0	0
Fair Value	728,450,000	689,382,000
Residential mortgage-backed
AVAILABLE-FOR-SALE
Amortized Cost	649,677,000	623,431,000
Gross Unrealized Gain	7,308,000	864,000
Gross Unrealized Loss	26,613,000	40,884,000
Allowance for Credit Losses	0	0
Fair Value	630,372,000	583,411,000
Commercial mortgage-backed
AVAILABLE-FOR-SALE
Amortized Cost	143,857,000	102,975,000
Gross Unrealized Gain	2,407,000	624,000
Gross Unrealized Loss	10,000	44,000
Allowance for Credit Losses	0	0
Fair Value	146,254,000	103,554,000
Other asset-backed
AVAILABLE-FOR-SALE
Amortized Cost	157,264,000	127,125,000
Gross Unrealized Gain	1,212,000	593,000
Gross Unrealized Loss	534,000	940,000
Allowance for Credit Losses	0	0
Fair Value	$ 157,942,000	$ 126,779,000

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

+ Details

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

- Definition

Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

+ Details

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

- References

No definition available.

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount excluding accrued interest, of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479130/326-30-45-1

+ Details

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

- Definition

Amortized cost excluding accrued interest, before allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

+ Details

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

- Definition

Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479130/326-30-45-1

+ Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USTreasuryAndGovernmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommercialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=ufcs_OtherAssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: