SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details)	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2017 USD ($) segment	Sep. 17, 2017 segment	Dec. 31, 2018 USD ($) state segment plan	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 01, 2019 USD ($)
Item Effected [Line Items]
Number of operating segments | segment	1	2	1
Percentage of the gains and profits from the Lloyds plan available to United Fire & Indemnity Company			100.00%
Securities on deposit as required by law	$ 1,492,928,000		$ 20,456,000	$ 1,492,928,000
Payment for income taxes			29,071,000	7,667,000	$ 24,034,000
Federal tax refund received			1,503,000	13,383,000	0
Interest payment			0	0	0
Increase (decrease) in DAC asset	(6,294,000)		0	(6,294,000)	(6,413,000)
Depreciation expense			4,455,000	3,805,000	5,266,000
Goodwill, impairment charge			0	0	0
Unrecognized tax benefit	0		$ 0	0	0
Number of equity compensation plans | plan			2
Accumulated other comprehensive income, net of tax	168,314,000		$ (30,472,000)	168,314,000
Retained earnings	608,700,000		$ 715,472,000	608,700,000
Future minimum lease payments as a percentage of total assets (less than)			1.00%
Minimum
Item Effected [Line Items]
Useful life			2 years
Maximum
Item Effected [Line Items]
Useful life			15 years
Continuing Operations - Property and Casualty Insurance
Item Effected [Line Items]
Number of states in which we are licensed as insurer | state			46
Amortization expense			$ 719,000	719,000	$ 719,000
Discontinued Operations - Life Insurance | Minimum
Item Effected [Line Items]
Liability for future policy benefits, interest rate			3.15%
Discontinued Operations - Life Insurance | Maximum
Item Effected [Line Items]
Liability for future policy benefits, interest rate			6.00%
Accounting Standards Update 2016-01
Item Effected [Line Items]
Accumulated other comprehensive income, net of tax	$ (191,244)			$ (191,244)
Net realized investment gain			$ 17,375
Accounting Standards Update 2016-01 | Pro Forma
Item Effected [Line Items]
Retained earnings			$ 242,100,000
Subsequent Event | Accounting Standards Update 2016-02
Item Effected [Line Items]
Operating lease liability						$ 20,100,000
Right-of-use asset						$ 19,700,000