PENSION AND OTHER POST-RETIREMENT BENEFIT PLANS - SCHEDULE OF PENSION PLAN ASSETS WITHIN THE FAIR VALUE HIERARCHY (Details) - Pension Benefits  - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 1,100,245	$ 1,053,438	$ 963,861
Fair Value, Measurements, Recurring
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	1,100,245	1,053,438
Defined Benefit Plan, Plan Assets Measured at Net Asset Value	1,078,345	1,039,879
Fair Value, Measurements, Recurring | Quoted prices in active markets of identical assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	613	365
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	21,287	13,194
Fair Value, Measurements, Recurring | Significant other unobservable inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	22,476	14,188
Defined Benefit Plan, Plan Assets Measured at Net Asset Value	576	629
Fair Value, Measurements, Recurring | Cash and cash equivalents | Quoted prices in active markets of identical assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	613	365
Fair Value, Measurements, Recurring | Cash and cash equivalents | Significant other observable inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	21,287	13,194
Fair Value, Measurements, Recurring | Cash and cash equivalents | Significant other unobservable inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | Global all-cap
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	264,909	248,222
Defined Benefit Plan, Plan Assets Measured at Net Asset Value	264,909	248,222
Fair Value, Measurements, Recurring | Global all-cap | Quoted prices in active markets of identical assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | Global all-cap | Significant other observable inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | Global all-cap | Significant other unobservable inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | U.S. government/agency
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	215,573	264,066
Defined Benefit Plan, Plan Assets Measured at Net Asset Value	215,573	264,066
Fair Value, Measurements, Recurring | U.S. government/agency | Quoted prices in active markets of identical assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | U.S. government/agency | Significant other observable inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | U.S. government/agency | Significant other unobservable inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	155,648	136,896
Defined Benefit Plan, Plan Assets Measured at Net Asset Value	155,648	136,896
Fair Value, Measurements, Recurring | Corporate bonds | Quoted prices in active markets of identical assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | Corporate bonds | Significant other observable inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | Corporate bonds | Significant other unobservable inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | International government/corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	32,586	32,407
Defined Benefit Plan, Plan Assets Measured at Net Asset Value	32,586	32,407
Fair Value, Measurements, Recurring | International government/corporate bonds | Quoted prices in active markets of identical assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | International government/corporate bonds | Significant other observable inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | International government/corporate bonds | Significant other unobservable inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | Diversified credit
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	160,829	103,793
Defined Benefit Plan, Plan Assets Measured at Net Asset Value	160,829	103,793
Fair Value, Measurements, Recurring | Diversified credit | Quoted prices in active markets of identical assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | Diversified credit | Significant other observable inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | Diversified credit | Significant other unobservable inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | Global diversified assets
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	117,290	146,681
Defined Benefit Plan, Plan Assets Measured at Net Asset Value	117,290	146,681
Fair Value, Measurements, Recurring | Global diversified assets | Quoted prices in active markets of identical assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | Global diversified assets | Significant other observable inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | Global diversified assets | Significant other unobservable inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | Global real estate investment trusts
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	60,083	53,159
Defined Benefit Plan, Plan Assets Measured at Net Asset Value	60,083	53,159
Fair Value, Measurements, Recurring | Global real estate investment trusts | Quoted prices in active markets of identical assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | Global real estate investment trusts | Significant other observable inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | Global real estate investment trusts | Significant other unobservable inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | Global infrastructure
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	70,851	54,026
Defined Benefit Plan, Plan Assets Measured at Net Asset Value	70,851	54,026
Fair Value, Measurements, Recurring | Global infrastructure | Quoted prices in active markets of identical assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | Global infrastructure | Significant other observable inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | Global infrastructure | Significant other unobservable inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 0	$ 0