Quarterly report pursuant to Section 13 or 15(d)

BENEFIT PLANS - Net Periodic Benefit Cost (Details)

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BENEFIT PLANS - Net Periodic Benefit Cost (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Pension Benefits        
Components of net periodic benefit expense [Abstract]        
Service cost $ 640 $ 1,425 $ 1,920 $ 3,475
Interest cost 7,478 7,978 22,433 21,474
Expected return on plan assets (13,803) (12,086) (41,409) (32,533)
Amortization of prior service cost 0 0 0 0
Amortization of gain (loss) 1,747 1,865 5,241 5,594
Settlements 5,049 3,400 10,049 10,200
Net periodic (benefit) cost 1,111 2,582 (1,766) 8,210
Post Retirement Benefits        
Components of net periodic benefit expense [Abstract]        
Service cost 22 16 65 16
Interest cost 98 79 296 188
Expected return on plan assets 0 0 0 0
Amortization of prior service cost (492) (492) (1,476) (1,476)
Amortization of gain (loss) (55) (72) (164) (216)
Settlements 0 0 0 0
Net periodic (benefit) cost $ (427) $ (469) $ (1,279) $ (1,488)