SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details)	9 Months Ended	12 Months Ended
	Sep. 17, 2017 segment	Dec. 31, 2019 USD ($) state segment plan variable_interest_entities	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jan. 01, 2019 USD ($)	Jan. 01, 2018 USD ($)
Item Effected [Line Items]
Number of operating segments | segment	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		$ 20,816,000	$ 20,456,000
Payment for income taxes		1,575,000	29,071,000	$ 7,667,000
Federal tax refund received		5,401,000	1,503,000	13,383,000
Interest payment		0	0	0
Increase (decrease) in DAC asset		0	0	6,294,000
Depreciation expense		10,482,000	4,455,000	3,805,000
Goodwill, impairment charge		0	0	0
Unrecognized tax benefit		$ 0	0	0
Number of variable interest entities | variable_interest_entities		1
Initial investment in variable interest entity		$ 7,500,000
VIE maximum exposure		$ 7,300,000
Number of equity compensation plans | plan		2
Right-of-use asset		$ 15,410,000
Operating lease liability		$ 15,851,000
Cumulative effect of change in accounting principle					$ (514,000)	$ 0
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		$ 709,000	$ 719,000	$ 719,000
Accounting Standards Update 2016-02
Item Effected [Line Items]
Right-of-use asset					19,800,000
Operating lease liability					20,300,000
Retained earnings
Item Effected [Line Items]
Cumulative effect of change in accounting principle					(514,000)	$ 191,244,000
Retained earnings | Accounting Standards Update 2016-01
Item Effected [Line Items]
Cumulative effect of change in accounting principle					126,000
Retained earnings | Accounting Standards Update 2016-02
Item Effected [Line Items]
Cumulative effect of change in accounting principle					$ 388,000