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RETIREMENT BENEFITS - Components of Net Periodic Benefit Cost (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Service cost $ 13,638 $ 12,505 $ 14,238
Interest cost 23,074 28,316 25,316
Expected return on plan assets (72,122) (60,567) (68,575)
Amortization of prior service cost (credit) 205 115 173
Amortization of actuarial losses (gains) 11,859 16,399 7,378
Net periodic benefit credit (23,346) (3,232) (21,470)
Other Postretirement Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 88 80 99
Interest cost 566 759 640
Expected return on plan assets 0 0 0
Amortization of prior service cost (credit) (1,937) (2,330) (1,392)
Amortization of actuarial losses (gains) (339) (488) (506)
Net periodic benefit credit $ (1,622) $ (1,979) $ (1,159)