EMPLOYEE BENEFIT PLANS - Changes in Plan Assets, Benefit Obligations, and Funded Status (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Change in plan assets:
Other adjustments	$ (9,903)	$ 4,988	$ 5,733
Pension Benefits
Change in projected benefit obligation:
Beginning of year	833,939	812,029
Service cost	35,055	36,002	26,718
Interest cost	21,667	25,741	26,966
Actuarial (gain) loss	13,520	(23,470)
Plan amendment	0	(833)
Benefits paid, net of retiree premiums	(16,704)	(15,530)
End of year	887,477	833,939	812,029
Change in plan assets:
Fair value of plan assets at beginning of year	716,794	573,575
Actual return on plan assets	84,488	121,751
Employer contributions	25,891	36,998
Retiree contributions and Medicare part D subsidies	0	0
Benefits paid	(16,704)	(15,530)
Other adjustments	0	0
Fair value of plan assets at end of year	810,469	716,794	573,575
Reconciliation of funded status
Funded status	(77,008)	(117,145)
Unrecognized actuarial loss (gain)	12,323	52,816
Unrecognized prior service cost	4,174	5,181
Net amount recognized	(60,511)	(59,148)
Short-term portion of the pension benefits	2,100	2,100
Other Benefits
Change in projected benefit obligation:
Beginning of year	130,658	150,515
Service cost	6,072	7,945	7,475
Interest cost	3,217	4,305	5,441
Actuarial (gain) loss	5,276	(30,485)
Plan amendment	0	0
Benefits paid, net of retiree premiums	(2,753)	(1,622)
End of year	142,470	130,658	150,515
Change in plan assets:
Fair value of plan assets at beginning of year	147,057	128,554
Actual return on plan assets	23,160	13,272
Employer contributions	1,972	6,853
Retiree contributions and Medicare part D subsidies	2,199	2,075
Benefits paid	(5,057)	(3,849)
Other adjustments	105	152
Fair value of plan assets at end of year	169,436	147,057	$ 128,554
Reconciliation of funded status
Funded status	26,966	16,399
Unrecognized actuarial loss (gain)	(29,327)	(20,699)
Unrecognized prior service cost	1,738	1,932
Net amount recognized	$ (623)	$ (2,368)