DEBT -Narrative (Details) (USD $)	3 Months Ended		0 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Jul. 02, 2014	Jun. 15, 2011	Dec. 31, 2014
Debt Instrument [Line Items]
Amortization of debt issuance costs	$ 530,000	$ 608,000
Term loan, amount outstanding	150,000,000
Carrying amount of liability	215,177,000				213,121,000
July 2014 Amendment
Debt Instrument [Line Items]
Senior credit facility, maximum borrowing capacity			900,000,000
Additional commitments			200,000,000
Cash balance threshold above which excess amount is not subject to any restriction of use or investment			40,000,000
Deferred finance costs, gross			3,200,000
Amortization of debt issuance costs			300,000
July 2014 Amendment | Minimum
Debt Instrument [Line Items]
Line of credit, commitment fee percentage			0.15%
July 2014 Amendment | Maximum
Debt Instrument [Line Items]
Line of credit, commitment fee percentage			0.30%
Proceeds from lines of credit			422,000,000
July 2014 Amendment | Standby Letters of Credit
Debt Instrument [Line Items]
Senior credit facility, maximum borrowing capacity			60,000,000
July 2014 Amendment | Revolving Credit Facility
Debt Instrument [Line Items]
Senior credit facility, maximum borrowing capacity			750,000,000
Proceeds from lines of credit			272,000,000
July 2014 Amendment | Swingline Loan
Debt Instrument [Line Items]
Senior credit facility, maximum borrowing capacity			60,000,000
Term Loan
Debt Instrument [Line Items]
Weighted average interest rate on debt	1.70%
Long-term debt, fair value	141,300,000
June 2011 Amendment | Revolving Credit Facility
Debt Instrument [Line Items]
Senior credit facility, maximum borrowing capacity			600,000,000
Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility outstanding	251,900,000				266,900,000
Weighted average interest rate on debt					1.70%
Available borrowings under senior secured revolving credit facility	498,100,000
Line of credit facility, fair value of amount outstanding	235,800,000
2016 Convertible Senior Notes
Debt Instrument [Line Items]
Principal amount outstanding	230,000,000			230,000,000	230,000,000
Interest rate on debt				1.625%
Portion of the debt proceeds that was classified as equity at the time of the offering				43,200,000
Effective interest rate implicit in the liability component				5.60%
Carrying amount of liability	215,200,000				213,100,000
Unamortized discount	14,800,000				16,900,000
Fair value of outstanding borrowings	272,300,000
Common stock based on initial conversion rate ratio (in shares)				17.4092
Principal amount to be considered for conversion purpose				1,000
Initial conversion price, per share				$ 57.44
Maximum selling price of company's common stock				150.00%
Principal amount of notes per average trading price				1,000
Maximum average conversion value of the Notes				98.00%
Strike price of the call transaction (in dollars per share)				$ 57.44
Strike price of warrant transactions (in dollars per share)				$ 70.05
Term Loan | July 2014 Amendment
Debt Instrument [Line Items]
Senior credit facility, maximum borrowing capacity			150,000,000
Proceeds from lines of credit			$ 150,000,000
Federal Funds | July 2014 Amendment
Debt Instrument [Line Items]
Interest rates available to the Company at its option			0.50%
(LIBOR) | July 2014 Amendment
Debt Instrument [Line Items]
Interest rates available to the Company at its option			1.00%
Eurodollar | July 2014 Amendment | Minimum
Debt Instrument [Line Items]
Interest rates available to the Company at its option			1.00%
Eurodollar | July 2014 Amendment | Maximum
Debt Instrument [Line Items]
Interest rates available to the Company at its option			1.75%