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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Investment income									$ 52,894	$ 51,190	$ 55,284
Total revenues	$ 252,062	$ 291,910	$ 275,399	$ 250,795	$ 273,355	$ 269,617	$ 258,487	$ 251,278	1,070,166	1,052,737	996,362
Expenses
Net income									27,650	51,023	49,904
Other comprehensive income (loss)
Change in unrealized appreciation on investments held by subsidiary									(50,985)	72,251	13,017
Change in liability for underfunded employee benefit plans									25,513	(26,122)	30,045
Other comprehensive income (loss), before tax and reclassification adjustments									(25,472)	46,129	43,062
Income tax effect									5,349	(17,540)	(15,072)
Other comprehensive income (loss), after tax, before reclassification adjustments									(20,123)	28,589	27,990
Reclassification adjustment for net realized (gains) losses included in income									784	(6,390)	(4,520)
Reclassification adjustment for employee benefit costs included in expense									6,642	5,408	5,486
Total reclassification adjustments, before tax									7,426	(982)	966
Income tax effect									(1,559)	344	(338)
Comprehensive income									13,394	78,974	78,522
United Fire Group, Inc.
Revenues
Investment income									396	133	66
Total revenues									396	133	66
Expenses
Other operating expenses									95	103	73
Total expenses									95	103	73
Income (loss) before income taxes and equity in net income of subsidiary									301	30	(7)
Federal income tax benefit									(1,165)	(1,060)	(3)
Net income (loss) before equity in net income of subsidiary									1,466	1,090	(4)
Equity in net income of subsidiary									26,184	49,933	49,908
Net income									27,650	51,023	49,904
Other comprehensive income (loss)
Change in unrealized appreciation on investments held by subsidiary									(50,985)	72,251	13,017
Change in liability for underfunded employee benefit plans									25,513	(26,122)	30,045
Other comprehensive income (loss), before tax and reclassification adjustments									(25,472)	46,129	43,062
Income tax effect									5,349	(17,540)	(15,072)
Other comprehensive income (loss), after tax, before reclassification adjustments									(20,123)	28,589	27,990
Reclassification adjustment for net realized (gains) losses included in income									784	(6,390)	(4,520)
Reclassification adjustment for employee benefit costs included in expense									6,642	5,408	5,486
Total reclassification adjustments, before tax									7,426	(982)	966
Income tax effect									(1,559)	344	(338)
Total reclassification adjustments, after tax									5,867	(638)	628
Comprehensive income									$ 13,394	$ 78,974	$ 78,522