Schedule II. Condensed Financial Statements of Parent Company (Condensed Balance Sheet) (Phantom) (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Condensed Balance Sheet Statements, Captions [Line Items]
Held-to-maturity securities	$ 150	$ 150
Common stock, par value per share (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	75,000,000	75,000,000
Common stock, shares issued (in shares)	24,916,806	25,429,769
Common stock, shares outstanding (in shares)	24,916,806	25,429,769
United Fire Group, Inc.
Condensed Balance Sheet Statements, Captions [Line Items]
Held-to-maturity securities	$ 150	$ 150
Common stock, par value per share (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	75,000,000	75,000,000
Common stock, shares issued (in shares)	24,916,806	25,429,769
Common stock, shares outstanding (in shares)	24,916,806	25,429,769