Summary of Significant Accounting Policies (Narratives) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended										0 Months Ended				12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012	Dec. 31, 2011		Dec. 31, 2010	Dec. 31, 2012 Property and Casualty Insurance [Member] states	Dec. 31, 2011 Property and Casualty Insurance [Member]	Dec. 31, 2010 Property and Casualty Insurance [Member]	Dec. 31, 2012 Life Insurance [Member] states	Dec. 31, 2011 Life Insurance [Member]	Dec. 31, 2010 Life Insurance [Member]	Mar. 28, 2011 Mercer Insurance Group [Member]	Mar. 28, 2011 Payments to the Former Executive Officers [Member] Mercer Insurance Group [Member]	Feb. 01, 2012 United Fire & Casualty Company [Member] Febuary 2012 Reorganization [Member]	Feb. 01, 2012 United Fire Group, Inc. [Member] Febuary 2012 Reorganization [Member]	Dec. 31, 2012 Minimum [Member]	Dec. 31, 2012 Maximum [Member]	Dec. 31, 2012 Accounting Standards Update 2010-26 [Member]
Item Effected [Line Items]
Number of states in which we are licensed as insurer																					43			36
Business Combinations [Abstract]
Percentage of outstanding common stock acquired																											100.00%
Total consideration of business combination																											$ 191,475
Short-term debt used for acquisition funding																											79,900
Transaction costs																											8,318	5,540
Common stock, par value per share	$ 0.001								$ 0.001								$ 0.001	$ 0.001											$ 3.3333333	$ 0.001
Percentage of the gains and profits from the Lloyds plan available to United Fire & Indemnity Company																	100.00%
Traditional life insurance, Interest rate assumptions, Lower range																								4.50%
Traditional life insurance, Interest rate assumptions, Upper range																								6.00%
Securities on deposit as required by law	1,736,466								1,682,525								1,736,466	1,682,525
Pre-tax OTTI																	4	395		459
Payment for income taxes																	11,920	570		14,124
Federal tax refund received																	15,798			13,491
Interest payment																	961	1,926
Decrease to Deferred Acquisition Cost asset related to shadow DAC adjustment																	(38,695)	(33,874)
Income Statement Impact of Updated Accounting Guidance on a Prospective Basis [Abstract]
Additional expense on pretax basis																	767,169	717,723		532,689	637,648	598,684	420,374	130,135	119,712	112,810							10,291
Increase to other underwriting expenses																	81,125	58,757		39,305													25,528
Decrease to amortization of deferred policy acquisition recoverability																	140,161	127,413		113,371	132,771	118,189	102,636	7,390	9,224	10,735							15,237
Decrease to net income	(2,418)		8,730		14,716		19,184		16,891		(4,776)		(17,914)		5,810		40,212	11		47,513	33,512	(7,639)	34,726	6,700	7,650	12,787							6,689
Decrease to net income per share	$ (0.10)	[1]	$ 0.34	[1]	$ 0.58	[1]	$ 0.75	[1]	$ 0.66	[1]	$ (0.19)	[1]	$ (0.69)	[1]	$ 0.22	[1]	$ 1.58	$ 0.00	[1]	$ 1.81													$ 0.26
Depreciation expense																	5,440	3,661		2,812
Useful life of intangible assets																															2 years	15 years
Amortization expense																					$ 2,539	$ 1,922	$ 60

[1] The sum of the quarterly reported amounts may not equal the full year, as each is computed independently.