SUMMARY OF INVESTMENTS - Carrying Value of Commercial Mortgage Loans and Additional Information (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2025	Dec. 31, 2024
Financing Receivable, Credit Quality Indicator [Line Items]
Total amortized cost	$ 40,480	$ 40,967
Allowance for mortgage loan losses	(1,147)	(45)
Mortgage loans, net	39,333	40,922
Total mortgage loans \| Commercial Mortgage Loans by Region
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net	$ 40,480	$ 40,967
Percent of Total	100.00%	100.00%
Total mortgage loans \| Commercial Mortgage Loans by Region \| East North Central
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net	$ 3,176	$ 3,218
Percent of Total	7.80%	7.90%
Total mortgage loans \| Commercial Mortgage Loans by Region \| Southern Atlantic
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net	$ 16,868	$ 17,021
Percent of Total	41.80%	41.40%
Total mortgage loans \| Commercial Mortgage Loans by Region \| East South Central
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net	$ 7,048	$ 7,257
Percent of Total	17.40%	17.70%
Total mortgage loans \| Commercial Mortgage Loans by Region \| New England
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net	$ 6,588	$ 6,588
Percent of Total	16.30%	16.10%
Total mortgage loans \| Commercial Mortgage Loans by Region \| Middle Atlantic
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net	$ 2,041	$ 2,078
Percent of Total	5.00%	5.10%
Total mortgage loans \| Commercial Mortgage Loans by Region \| Mountain
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net	$ 1,992	$ 1,992
Percent of Total	4.90%	4.90%
Total mortgage loans \| Commercial Mortgage Loans by Region \| West North Central
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net	$ 2,767	$ 2,813
Percent of Total	6.80%	6.90%
Total mortgage loans \| Commercial Mortgage Loans by Property Type
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net	$ 40,480	$ 40,967
Percent of Total	100.00%	100.00%
Total mortgage loans \| Commercial Mortgage Loans by Property Type \| Multifamily
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net	$ 8,229	$ 8,362
Percent of Total	20.30%	20.40%
Total mortgage loans \| Commercial Mortgage Loans by Property Type \| Office
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net	$ 10,378	$ 10,615
Percent of Total	25.70%	25.90%
Total mortgage loans \| Commercial Mortgage Loans by Property Type \| Industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net	$ 9,855	$ 9,912
Percent of Total	24.40%	24.20%
Total mortgage loans \| Commercial Mortgage Loans by Property Type \| Retail
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net	$ 9,977	$ 10,000
Percent of Total	24.60%	24.40%
Total mortgage loans \| Commercial Mortgage Loans by Property Type \| Mixed use/Other
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net	$ 2,041	$ 2,078
Percent of Total	5.00%	5.10%
Less than 65%
Financing Receivable, Credit Quality Indicator [Line Items]
Total amortized cost	$ 32,160	$ 32,499
65%-75%
Financing Receivable, Credit Quality Indicator [Line Items]
Total amortized cost	$ 8,320	$ 8,468

UNITED FIRE GROUP INC 10-Q