SUMMARY OF INVESTMENTS (Net Realized Investment Gains and Losses) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Gain (Loss) on Investments [Line Items]
Net realized investment gains (losses) from continuing operations	$ 4,055	$ 4,947	$ 1,124
AVAILABLE-FOR-SALE
Proceeds from sales	7,404	1,968	478
Gross realized gains	1,046	920	451
Gross realized losses	(20)	0	0
Discontinued Operations
Gain (Loss) on Investments [Line Items]
Net realized investment gains (losses) from continuing operations	4,008	1,156	1,722
AVAILABLE-FOR-SALE
Proceeds from sales	7,315	12,354	11,066
Gross realized gains	1,264	65	683
Gross realized losses	(78)	(639)	0
Continuing and Discontinuing Operations
Gain (Loss) on Investments [Line Items]
Net realized investment gains (losses) from continuing operations	8,063	6,103	2,846
Fixed maturities \| Available-for-sale
Gain (Loss) on Investments [Line Items]
Net realized investment gains (losses) from continuing operations	829	1,004	814
Fixed maturities \| Change in fair value
Gain (Loss) on Investments [Line Items]
Net realized investment gains (losses) from continuing operations	924	189	(1,352)
Fixed maturities \| Sales
Gain (Loss) on Investments [Line Items]
Net realized investment gains (losses) from continuing operations	244	931	1,381
Fixed maturities \| Other-than-temporary-impairment charges
Gain (Loss) on Investments [Line Items]
Net realized investment gains (losses) from continuing operations	0	0	0
Equity securities \| Available-for-sale
Gain (Loss) on Investments [Line Items]
Net realized investment gains (losses) from continuing operations	1,553	2,359	1,977
Equity securities \| Change in fair value
Gain (Loss) on Investments [Line Items]
Net realized investment gains (losses) from continuing operations	332	301	(448)
Equity securities \| Sales
Gain (Loss) on Investments [Line Items]
Net realized investment gains (losses) from continuing operations	57	(6)	66
Other long-term investments
Gain (Loss) on Investments [Line Items]
Net realized investment gains (losses) from continuing operations	0	0	(1,314)
Cash equivalents
Gain (Loss) on Investments [Line Items]
Net realized investment gains (losses) from continuing operations	0	169	0
Real Estate
Gain (Loss) on Investments [Line Items]
Net realized investment gains (losses) from continuing operations	$ 116	$ 0	$ 0

No definition available.

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

- Definition

This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

+ References

+ Details

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

- Definition

The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26853-111562

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a),(b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

+ Details

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

- Definition

The net realized gains or losses on investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.3(a))
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 325
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=75031664&loc=d3e22529-158502

+ Details

Name:	us-gaap_RealizedInvestmentGainsLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_StatementOperatingActivitiesSegmentAxis=us-gaap_SegmentDiscontinuedOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementOperatingActivitiesSegmentAxis=ufcs_ContinuingandDiscontinuingOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	invest_InvestmentAxis=us-gaap_FixedMaturitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_GainLossOnInvestmentsByCategoryAxis=us-gaap_AvailableforsaleSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_GainLossOnInvestmentsByCategoryAxis=ufcs_TradingAccountAssetsChangeInFairValueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_GainLossOnInvestmentsByCategoryAxis=ufcs_TradingAccountAssetsSalesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_GainLossOnInvestmentsByCategoryAxis=ufcs_OtherthantemporaryimpairmentChargesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	invest_InvestmentAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	invest_InvestmentAxis=ufcs_CategoriesOfInvestmentsMarketableSecuritiesOtherLongTermInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	invest_InvestmentAxis=us-gaap_CashEquivalentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	invest_InvestmentAxis=us-gaap_RealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: