EMPLOYEE BENEFITS (Net Periodic Benefit Cost) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Plan [Member]
Net periodic benefit cost
Service cost	$ 6,300	$ 5,129	$ 3,166
Interest cost	5,175	5,049	4,761
Expected return on plan assets	(5,772)	(5,345)	(5,288)
Amortization of prior service cost	0	8	10
Amortization of net loss	4,989	4,415	2,368
Net periodic benefit cost	10,692	9,256	5,017
Postretirement Benefit Plan [Member]
Net periodic benefit cost
Service cost	3,875	3,010	1,985
Interest cost	1,759	1,695	1,590
Expected return on plan assets	0	0	0
Amortization of prior service cost	0	(6)	(32)
Amortization of net loss	879	554	224
Net periodic benefit cost	6,513	5,253	3,767
Mercer Insurance Group [Member] | Pension Plan [Member]
Net periodic benefit cost
Net periodic benefit cost		$ 854