EMPLOYEE BENEFIT PLANS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Defined Benefit Pension Plan
EMPLOYEE BENEFIT PLANS
Service cost — benefits earned during the period	$ 3,348	$ 2,906
Interest cost on projected benefit obligation	2,191	2,737
Expected return on plan assets	(3,352)	(3,605)
Amortization of prior service cost	0	0
Amortization of actuarial losses	0	0
Preliminary net periodic benefit cost	2,187	2,038
Settlement/curtailment expense	0	0
Total net periodic benefit cost	$ 2,187	2,038
Defined Benefit Pension Plan | Minimum
EMPLOYEE BENEFIT PLANS
Adjusted funding target percentage to be maintained	80.00%
Excess Benefit Plan
EMPLOYEE BENEFIT PLANS
Service cost — benefits earned during the period	$ 334	313
Interest cost on projected benefit obligation	297	438
Expected return on plan assets	0	0
Amortization of prior service cost	0	0
Amortization of actuarial losses	118	0
Preliminary net periodic benefit cost	749	751
Settlement/curtailment expense	0	0
Total net periodic benefit cost	$ 749	$ 751