PENSION AND OTHER POST-EMPLOYMENT BENEFITS (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Benefits
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Service cost	$ 175	$ 468	$ 525	$ 1,404
Interest cost	2,390	2,416	7,170	7,248
Expected return on plan assets	(4,615)	(3,862)	(13,845)	(11,086)
Amortization of prior service credit	0	0	0	0
Recognized actuarial loss (gain)	154	123	462	369
Net periodic benefit income	(1,896)	(855)	(5,688)	(2,065)
Other Benefits
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Service cost	0	0	0	0
Interest cost	43	49	129	147
Expected return on plan assets	0	0	0	0
Amortization of prior service credit	(371)	(280)	(1,113)	(840)
Recognized actuarial loss (gain)	1	(62)	3	(186)
Net periodic benefit income	$ (327)	$ (293)	$ (981)	$ (879)