PENSION AND OTHER POSTRETIREMENT BENEFITS - DEFINED CONTRIBUTION PLAN (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) $ / employees	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Amount expensed and contributed for the matching provision | $	$ 1.3	$ 1.2	$ 1.2
Employee Qualifying For Defined Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Match of participants' contributions	50.00%
Match of participants contributions of base compensation (up to)	6.00%
Employee Not Qualifying For Defined Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Match of participants' contributions	50.00%
Match of participants contributions of base compensation (up to)	8.00%
Additional year-end compensation	1,500
Threshold of service	10 years
Additional year-end compensation	2,000