EMPLOYEE RETIREMENT PLANS (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension plans [Member] | Emc Insurance Companies [Member]
Components of net periodic benefit cost [Abstract]
Service cost	$ 3,783	$ 3,639	$ 11,351	$ 10,824
Interest cost	2,798	2,551	8,393	7,620
Expected return on plan assets	(5,192)	(4,841)	(15,574)	(14,521)
Amortization of net actuarial loss	911	1,111	2,732	3,233
Amortization of prior service cost (credit)	5	9	15	24
Net periodic benefit cost (income)	2,305	2,469	6,917	7,180
Pension plans [Member] | EMC Insurance Group, Inc. [Member]
Components of net periodic benefit cost [Abstract]
Net periodic benefit cost (income)	692	1,100	2,100	2,500
Entity's share of estimated contributions to employee benefit plan	2,700		2,700
Postretirement benefit plans [Member] | Emc Insurance Companies [Member]
Components of net periodic benefit cost [Abstract]
Service cost	341	319	1,022	955
Interest cost	570	553	1,710	1,661
Expected return on plan assets	(1,077)	(1,056)	(3,233)	(3,168)
Amortization of net actuarial loss	342	374	1,028	1,121
Amortization of prior service cost (credit)	(2,788)	(2,835)	(8,365)	(8,504)
Net periodic benefit cost (income)	(2,612)	(2,645)	(7,838)	(7,935)
Postretirement benefit plans [Member] | EMC Insurance Group, Inc. [Member]
Components of net periodic benefit cost [Abstract]
Net periodic benefit cost (income)	(736)	$ (937)	(2,200)	$ (2,400)
Entity's share of estimated contributions to employee benefit plan	$ 0		$ 0