Annual report pursuant to Section 13 and 15(d)

BENEFIT PLANS - Projected Benefit Obligation (Details)

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BENEFIT PLANS - Projected Benefit Obligation (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Pension Benefits      
Change in Benefit Obligation [Roll Forward]      
Projected benefit obligation at beginning of measurement year $ 754,714 $ 799,594  
Service cost 4,100 1,830 $ 1,740
Interest cost 26,992 31,937 32,398
Benefits paid (18,306) (17,246)  
Settlements (21,684) (27,976)  
Medicare subsidies 0 0  
Actuarial assumptions and gains and losses (9,470) (33,425)  
Total changes (18,368) (44,880)  
Projected benefit obligation at end of measurement year 736,346 754,714 799,594
Post-Retirement Benefits      
Change in Benefit Obligation [Roll Forward]      
Projected benefit obligation at beginning of measurement year 8,025 15,963  
Service cost 0 0 0
Interest cost 219 506 856
Benefits paid (1,915) (2,211)  
Settlements 0 (6,993)  
Medicare subsidies 0 117  
Actuarial assumptions and gains and losses 963 643  
Total changes (733) (7,938)  
Projected benefit obligation at end of measurement year $ 7,292 $ 8,025 $ 15,963