INCOME TAXES - UNRECOGNIZED TAX BENEFITS (Details)	12 Months Ended
	Dec. 31, 2017 USD ($)
Unrecognized tax benefits
Unrecognized tax benefits, if recognized would impact effective tax rate	$ 15,900,000
Balance at the beginning of the period	14,700,000
Increase related to current year tax positions	1,200,000
Balance at the end of the period	$ 15,900,000