SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details)	3 Months Ended		9 Months Ended	12 Months Ended
	Dec. 31, 2017 USD ($) segment state	Dec. 31, 2017 USD ($) state	Sep. 17, 2017 segment	Dec. 31, 2017 USD ($) state plan	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) holding_company
Item Effected [Line Items]
Number of operating segments | segment	1		2
Percentage of the gains and profits from the Lloyds plan available to United Fire & Indemnity Company				100.00%
Number of holding companies dissolved | holding_company						3
Securities on deposit as required by law	$ 1,492,928,000	$ 1,492,928,000		$ 1,492,928,000	$ 1,509,339,000
Payment for income taxes				7,667,000	24,034,000	$ 39,497,000
Federal tax refund received				13,383,000	0	919,000
Interest payment				0	0	0
Increase (decrease) in DAC asset	(6,294,000)	(6,294,000)		(6,294,000)	(6,413,000)	(2,003,000)
Depreciation expense				3,805,000	5,266,000	5,704,000
Goodwill, impairment charge				0	0	0
Unrecognized tax benefit	0	0		$ 0	0	0
Number of equity compensation plans | plan				2
Excess tax benefit		149,000		$ 695,000
Accumulated effect of change in enacted tax rate				31,308,000
Accumulated other comprehensive income, net of tax	168,314,000	168,314,000		168,314,000	109,055,000
Retained earnings	608,700,000	608,700,000		608,700,000	616,322,000
Future minimum lease payments	$ 22,525,000	$ 22,525,000		$ 22,525,000
Future minimum lease payments as a percentage of total assets (less than)	1.00%	1.00%		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	46		46
Amortization expense				$ 769,000	769,000	769,000
Discontinued Operations - Life Insurance
Item Effected [Line Items]
Number of states in which we are licensed as insurer | state	37	37		37
Discontinued Operations - Life Insurance | Minimum
Item Effected [Line Items]
Liability for future policy benefits, interest rate	3.15%	3.15%		3.15%
Discontinued Operations - Life Insurance | Maximum
Item Effected [Line Items]
Liability for future policy benefits, interest rate	6.00%	6.00%		6.00%
Accounting Standards Update 2016-01 [Member] | Pro Forma
Item Effected [Line Items]
Accumulated other comprehensive income, net of tax	$ (242,100,000)	$ (242,100,000)		$ (242,100,000)
Retained earnings	$ 242,100,000	$ 242,100,000		242,100,000
Accumulated other comprehensive income, net of tax
Item Effected [Line Items]
Accumulated effect of change in enacted tax rate				31,308,000	0	0
Retained earnings
Item Effected [Line Items]
Accumulated effect of change in enacted tax rate				$ (31,308,000)	$ 0	$ 0