Employee Benefits (Fair Value of Plan Assets) (Details) (Pension Plan [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	$ 75,276	$ 65,267	$ 62,730
Fair Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	65,253	54,232
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	55,060	44,993
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	10,193	9,239
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	4,830	4,000
Corporate Bonds [Member] | Fair Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	4,830	4,000
Corporate Bonds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Corporate Bonds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	4,830	4,000
Corporate Bonds [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Redeemable Preferred Stocks [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	1,113	2,067
Redeemable Preferred Stocks [Member] | Fair Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	1,113	2,067
Redeemable Preferred Stocks [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	1,113	2,067
Redeemable Preferred Stocks [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Redeemable Preferred Stocks [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
United Fire Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	4,078
United Fire Common Stock [Member] | Fair Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value		4,078
United Fire Common Stock [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value		4,078
United Fire Common Stock [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value		0
United Fire Common Stock [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value		0
Unaffiliated Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	41,091	34,085
Unaffiliated Common Stock [Member] | Fair Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	41,091	34,085
Unaffiliated Common Stock [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	41,091	34,085
Unaffiliated Common Stock [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Unaffiliated Common Stock [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Arbitrage Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	5,363	5,239
Arbitrage Fund [Member] | Fair Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	5,363	5,239
Arbitrage Fund [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Arbitrage Fund [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	5,363	5,239
Arbitrage Fund [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Money Market Funds [Member] | Fair Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	12,856	4,763
Money Market Funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	12,856	4,763
Money Market Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	0	0
Money Market Funds [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Assets measured at fair value	$ 0	$ 0