EMPLOYEE BENEFIT PLANS (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Defined Benefit Pension Plan
EMPLOYEE BENEFIT PLANS
Service cost — benefits earned during the period	$ 3,348,000	$ 2,906,000	$ 6,696,000	$ 5,812,000
Interest cost on projected benefit obligation	2,191,000	2,737,000	4,382,000	5,474,000
Expected return on plan assets	(3,352,000)	(3,605,000)	(6,704,000)	(7,211,000)
Amortization of prior service cost	0	0	0	0
Amortization of actuarial losses	0	0	0	0
Preliminary net periodic benefit cost	2,187,000	2,038,000	4,374,000	4,075,000
Settlement/curtailment expense	0	0	0	0
Total net periodic benefit costs	2,187,000	2,038,000	4,374,000	4,075,000
Pension contributions			$ 0
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	334,000	478,000	$ 668,000	791,000
Interest cost on projected benefit obligation	297,000	317,000	594,000	755,000
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	0	0	0	0
Amortization of actuarial losses	118,000	50,000	236,000	50,000
Preliminary net periodic benefit cost	749,000	845,000	1,498,000	1,596,000
Settlement/curtailment expense	0	1,500,000	0	1,500,000
Total net periodic benefit costs	$ 749,000	$ 2,345,000	$ 1,498,000	$ 3,096,000