STATUTORY REPORTING, CAPITAL REQUIREMENTS AND DIVIDENDS AND RETAINED EARNINGS RESTRICTIONS (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 02, 2016
Statutory Accounting Practices [Line Items]
Maximum borrowing capacity	$ 100,000,000
Payment of cash dividends	(27,337,000)	$ (24,591,000)	$ (21,658,000)
Subsidiaries
Statutory Accounting Practices [Line Items]
Intercompany dividend payments that are eliminated in Consolidated Financial Statements	13,300,000	26,000,000	16,500,000
United Fire & Casualty Company
Statutory Accounting Practices [Line Items]
Intercompany dividend payments that are eliminated in Consolidated Financial Statements	40,000,000	$ 24,000,000	$ 22,500,000
United Life
Statutory Accounting Practices [Line Items]
Statutory basis	1,497,955,000
Net assets on statutory basis, in excess of the legal reserve requirement	215,488,000
Revolving Credit Facility
Statutory Accounting Practices [Line Items]
Maximum borrowing capacity	50,000,000			$ 50,000,000
State of Iowa Insurance Department
Statutory Accounting Practices [Line Items]
Maximum dividend distribution without prior approval	$ 35,744,000