EMPLOYEE RETIREMENT PLANS (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pension plans [Member] | Emc Insurance Companies [Member]
Components of net periodic benefit cost [Abstract]
Service cost	$ 4,300	$ 3,708	$ 8,426	$ 7,568
Interest cost	2,698	2,800	5,363	5,595
Expected return on plan assets	(6,048)	(5,191)	(12,026)	(10,382)
Amortization of net actuarial loss	143	913	268	1,821
Amortization of prior service cost (credit)	0	5	0	10
Net periodic benefit cost (income)	1,093	2,235	2,031	4,612
Pension plans [Member] | EMC Insurance Group, Inc. [Member]
Components of net periodic benefit cost [Abstract]
Net periodic benefit cost (income)	327	670	609	1,383
Entity's share of estimated contributions to employee benefit plan	600		600
Postretirement benefit plans [Member] | Emc Insurance Companies [Member]
Components of net periodic benefit cost [Abstract]
Service cost	368	340	736	681
Interest cost	521	570	1,042	1,140
Expected return on plan assets	(1,203)	(1,078)	(2,407)	(2,156)
Amortization of net actuarial loss	233	343	467	686
Amortization of prior service cost (credit)	(2,782)	(2,788)	(5,564)	(5,577)
Net periodic benefit cost (income)	(2,863)	(2,613)	(5,726)	(5,226)
Postretirement benefit plans [Member] | EMC Insurance Group, Inc. [Member]
Components of net periodic benefit cost [Abstract]
Net periodic benefit cost (income)	(806)	$ (736)	(1,612)	$ (1,472)
Entity's share of estimated contributions to employee benefit plan	$ 0		$ 0