EMPLOYEE RETIREMENT PLANS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension plans [Member] | Emc Insurance Companies [Member]
Components of net periodic benefit cost [Abstract]
Service cost	$ 4,126	$ 3,860
Interest cost	2,665	2,795
Expected return on plan assets	(5,978)	(5,191)
Amortization of net actuarial loss	125	908
Amortization of prior service cost (credit)	0	5
Net periodic benefit cost (income)	938	2,377
Pension plans [Member] | EMC Insurance Group, Inc. [Member]
Components of net periodic benefit cost [Abstract]
Net periodic benefit cost (income)	282	713
Entity's share of estimated contributions to employee benefit plan	2,400
Postretirement benefit plans [Member] | Emc Insurance Companies [Member]
Components of net periodic benefit cost [Abstract]
Service cost	368	341
Interest cost	521	570
Expected return on plan assets	(1,204)	(1,078)
Amortization of net actuarial loss	234	343
Amortization of prior service cost (credit)	(2,782)	(2,789)
Net periodic benefit cost (income)	(2,863)	(2,613)
Postretirement benefit plans [Member] | EMC Insurance Group, Inc. [Member]
Components of net periodic benefit cost [Abstract]
Net periodic benefit cost (income)	(806)	$ (736)
Entity's share of estimated contributions to employee benefit plan	$ 0