BENEFIT PLANS (Fair values of Pension Plan Assets) (Details) - Pension Benefits [Member] - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		$ 840,901	$ 749,515	$ 745,686
Interest In Common/Collective Trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		416,397	358,345
Venture Capital And Partnerships [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		84,852	86,745
Investments In The Fair Value Hierarchy [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		339,652	304,425
Investments In The Fair Value Hierarchy [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		178,512	162,894
Investments In The Fair Value Hierarchy [Member] | Commodity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		17,041	16,594
Investments In The Fair Value Hierarchy [Member] | Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		144,099	124,937
Investments In The Fair Value Hierarchy [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[1]	1,089	530
Investments In The Fair Value Hierarchy [Member] | Level 1 [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[1]	0	0
Investments In The Fair Value Hierarchy [Member] | Level 1 [Member] | Commodity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[1]	0	0
Investments In The Fair Value Hierarchy [Member] | Level 1 [Member] | Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[1]	1,089	530
Investments In The Fair Value Hierarchy [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[1]	338,563	303,895
Investments In The Fair Value Hierarchy [Member] | Level 2 [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[1]	178,512	162,894
Investments In The Fair Value Hierarchy [Member] | Level 2 [Member] | Commodity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[1]	17,041	16,594
Investments In The Fair Value Hierarchy [Member] | Level 2 [Member] | Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[1]	143,010	124,407
Investments In The Fair Value Hierarchy [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[1]	0	0
Investments In The Fair Value Hierarchy [Member] | Level 3 [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[1]	0	0
Investments In The Fair Value Hierarchy [Member] | Level 3 [Member] | Commodity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[1]	0	0
Investments In The Fair Value Hierarchy [Member] | Level 3 [Member] | Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[1]	$ 0	$ 0

[1] See Note 1 under the caption Fair Value Measurements for a description of the fair value hierarchy.