DEBT - Narrative (Details) - Credit Facility - Secured Debt - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 400,000,000	$ 400,000,000
Term of agreement	5 years
Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 300,000,000
Line of credit facility, accordion feature, increase limit	100,000,000
Line of credit facility, accordion feature, higher borrowing capacity option	$ 500,000,000
Average interest rate	4.59%	4.00%
Commitment fee percentage	0.50%
Term Loan Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 100,000,000
Standby Letters of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity	20,000,000
Swingline Sub-facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 20,000,000