LONG-TERM DEBT (Details) - USD ($)			3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2016	Mar. 04, 2016	Mar. 03, 2016	Aug. 10, 2015
Debt Instrument
Borrowings outstanding	$ 1,540,940,000	$ 1,449,178,000	$ 1,540,940,000
Revolving Credit Facility
Debt Instrument
Maximum borrowing capacity	$ 300,000,000.0		$ 300,000,000.0	$ 300,000,000.0	$ 130,000,000.0
Debt, Weighted Average Interest Rate	2.70%	2.60%	2.70%
Commitment fee on undrawn portion of revolving credit facility (as a percent)	0.50%	0.50%
Line of credit facility, remaining borrowing capacity	$ 161,400,000		$ 161,400,000
Amounts drawn on lines of credit during period			90,000,000
Letter Of Credit
Debt Instrument
Outstanding letters of credit fee (as a percent)	2.50%	2.50%
Letters of credit outstanding	$ 5,600,000		5,600,000
Term Loan Facility
Debt Instrument
Maximum borrowing capacity	$ 1,200,000,000.0		$ 1,200,000,000.0
Effective interest rate (as a percent)	3.25%	3.25%	3.25%
Borrowings outstanding	$ 1,173,398,000	$ 1,174,369,000	$ 1,173,398,000
Convertible Senior Notes | 1.5% Convertible Senior Notes, Due 2020
Debt Instrument
Principal	287,500,000	287,500,000	287,500,000			$ 287,500,000.0
Interest rate (as a percent)						1.50%
Borrowings outstanding	237,581,000	235,085,000	237,581,000
Credit Facility | Revolving Credit Facility
Debt Instrument
Debt issuance costs, gross				$ 1,700,000
Borrowings outstanding	$ 133,000,000	$ 43,000,000	$ 133,000,000