PENSION AND OTHER POSTRETIREMENT BENEFITS - DEFINED CONTRIBUTION PLAN (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) $ / employees	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Amount expensed and contributed for matching provision of Savings Plan | $	$ 2.1	$ 2.0	$ 1.7
Employees eligible for defined benefit pension plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Maximum annual contribution percentage	50.00%
Employer matching contribution, percentage	6.00%
Employees ineligible for defined benefit pension plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Maximum annual contribution percentage	50.00%
Employer matching contribution, percentage	8.00%
Year-end contribution (in USD per employee)	1,500
Service threshold to determine year-end contribution (more than) (in years)	10 years
Year-end contribution for employees with more then ten years of service	2,000