PENSION AND OTHER POST-EMPLOYMENT BENEFITS - Fair Value of Pension Plan Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	$ 273,895	$ 263,027
U.S. equity securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	75,944	103,649
Non-U.S. equity securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	37,042	36,936
Fixed income funds and cash investment funds
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	160,909	122,442
Level 1
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	123,867	263,027
Level 1 | U.S. equity securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	0	103,649
Level 1 | Non-U.S. equity securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	0	36,936
Level 1 | Fixed income funds and cash investment funds
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	123,867	122,442
Level 2
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	150,028	0
Level 2 | U.S. equity securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	75,944	0
Level 2 | Non-U.S. equity securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	37,042	0
Level 2 | Fixed income funds and cash investment funds
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	37,042	0
Level 3
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	0	0
Level 3 | U.S. equity securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	0	0
Level 3 | Non-U.S. equity securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	0	0
Level 3 | Fixed income funds and cash investment funds
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	$ 0	$ 0