DEBT, CREDIT FACILITY, AND CAPITAL LEASE OBLIGATIONS (Credit Facility) (Details)	1 Months Ended	12 Months Ended
	Oct. 31, 2015 USD ($) credit_extension	Dec. 31, 2017 USD ($)	Feb. 15, 2017 USD ($)	Dec. 31, 2010 USD ($)
Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility borrowing capacity	$ 250,000,000
Line of credit facility, number of extensions Allowed | credit_extension	2
Line of credit facility, extension period (in years)	1 year
Interest rate spread on LIBOR borrowing (in percentage)		1.00%
Interest rate in addition to alternate base rate for alternate base rate loans		0.00%
Line of credit facility, fair value of amount outstanding		$ 35,000,000
Remaining borrowing capacity			$ 232,000,000
Line of Credit | Revolving Credit Facility LOC Sublimit
Debt Instrument [Line Items]
Line of credit facility borrowing capacity	$ 50,000,000
Line of Credit | Revolving Credit Facility 2014 and 2010
Debt Instrument [Line Items]
Line of credit facility borrowing capacity	270,000,000
Line of Credit | Term Loan
Debt Instrument [Line Items]
Line of credit facility borrowing capacity	$ 130,000,000
Letter of Credit
Debt Instrument [Line Items]
Letter of credit, issued in support of tax exempt bonds				$ 37,000,000
Letter of credit, interest rate (in percentage)		0.75%