EMPLOYEE BENEFIT PLANS (Changes in Benefit Obligations, Fair Value of Plan Assets, and Funded Status of Plan) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	$ 185,231	$ 135,508
Service cost	47,344	40,572	$ 36,359
Interest cost	5,793	4,336	3,096
Plan amendments	0	462
Plan settlements	0	(4,881)
Benefit payments	7,214	4,034
Actuarial loss (gain)	(12,811)	13,268
Projected benefit obligation at end of year	218,343	185,231	135,508
Change in plan assets:
Fair value of plan assets at beginning of year	121,652	75,367
Actual return on plan assets	(6,148)	14,019
Benefits paid	7,214	4,034
Plan settlements	0	(4,881)
Employer contributions	35,081	41,181
Fair value of plan assets at end of year	143,371	121,652	75,367
Reconciliation of funded status:
Fair value of plan assets at end of year	121,652	75,367	75,367	$ 143,371	$ 121,652
Less benefit obligation at end of year	185,231	135,508	135,508	218,343	185,231
Funded status at end of year				(74,972)	(63,579)
Post Retirement Medical Plan [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	21,527	22,740
Service cost	1,148	1,263	1,047
Interest cost	620	688	528
Plan amendments	0	0
Plan settlements	0	0
Benefit payments	562	693
Actuarial loss (gain)	(3,388)	(2,471)
Projected benefit obligation at end of year	19,345	21,527	22,740
Change in plan assets:
Fair value of plan assets at beginning of year	0	0
Actual return on plan assets	0	0
Benefits paid	562	693
Plan settlements	0	0
Employer contributions	562	693
Fair value of plan assets at end of year	0	0	0
Reconciliation of funded status:
Fair value of plan assets at end of year	0	0	0	0	0
Less benefit obligation at end of year	$ 21,527	$ 22,740	$ 22,740	19,345	21,527
Funded status at end of year				$ (19,345)	$ (21,527)