PENSION AND OTHER POST-EMPLOYMENT BENEFITS - Fair Value of Pension Plan Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	$ 233,930	$ 273,895
U.S. equity securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	54,484	75,944
Non-U.S. equity securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	28,036	37,042
Fixed income funds and cash investment funds
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	151,410	160,909
Level 1
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	121,663	123,867
Level 1 | U.S. equity securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	0	0
Level 1 | Non-U.S. equity securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	0	0
Level 1 | Fixed income funds and cash investment funds
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	121,663	123,867
Level 2
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	112,267	150,028
Level 2 | U.S. equity securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	54,484	75,944
Level 2 | Non-U.S. equity securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	28,036	37,042
Level 2 | Fixed income funds and cash investment funds
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	29,747	37,042
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