Schedule II. Condensed Financial Statements of Parent Company (Condensed Statement of Income and Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues
Investment income									$ 39,670	$ 60,414	$ 52,894
Total revenues	$ 310,898	$ 282,121	$ 297,803	$ 177,805	$ 293,374	$ 298,055	$ 304,197	$ 305,539	1,068,627	1,201,165	1,070,166
Expenses
Net income (loss)									(112,706)	14,820	27,650
Other comprehensive income (loss)
Change in unrealized appreciation on investments held by subsidiary									47,054	70,127	(50,985)
Change in liability for underfunded employee benefit plans of subsidiary									18,456	(20,924)	25,513
Other comprehensive income (loss), before tax and reclassification adjustments									65,510	49,203	(25,472)
Income tax effect									(13,757)	(10,334)	5,349
Reclassification adjustment for net realized (gains) losses included in income									(1,750)	1,521	784
Reclassification adjustment for employee benefit costs included in expense									4,289	4,497	6,642
Total reclassification adjustments, before tax									2,539	6,018	7,426
Income tax effect									(534)	(1,263)	(1,559)
Comprehensive income (loss)									(58,948)	58,444	13,394
United Fire Group, Inc.
Revenues
Investment income									141	295	396
Total revenues									141	295	396
Expenses
Other operating expenses									10	86	95
Total expenses									10	86	95
Income before income taxes and equity in net income of subsidiary									131	209	301
Federal income tax expense (benefit)									68	44	(1,165)
Net income before equity in net income (loss) of subsidiary									63	165	1,466
Equity in net income (loss) of subsidiary									(112,769)	14,655	26,184
Net income (loss)									(112,706)	14,820	27,650
Other comprehensive income (loss)
Change in unrealized appreciation on investments held by subsidiary									47,054	70,127	(50,985)
Change in liability for underfunded employee benefit plans of subsidiary									18,456	(20,924)	25,513
Other comprehensive income (loss), before tax and reclassification adjustments									65,510	49,203	(25,472)
Income tax effect									(13,757)	(10,334)	5,349
Other comprehensive income (loss), after tax, before reclassification adjustments									51,753	38,869	(20,123)
Reclassification adjustment for net realized (gains) losses included in income									(1,750)	1,521	784
Reclassification adjustment for employee benefit costs included in expense									4,289	4,497	6,642
Total reclassification adjustments, before tax									2,539	6,018	7,426
Income tax effect									(534)	(1,263)	(1,559)
Total reclassification adjustments, after tax									2,005	4,755	5,867
Comprehensive income (loss)									$ (58,948)	$ 58,444	$ 13,394