DEBT (Narrative) (Details) (USD $)	12 Months Ended			0 Months Ended		1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jun. 08, 2011	Jul. 02, 2014	Jun. 30, 2012	May 11, 2012	Jun. 21, 2013	Jun. 15, 2011	Jun. 11, 2007
Debt Instrument [Line Items]
Amortization of debt issuance costs	$ 2,571,000	$ 2,298,000	$ 2,725,000
Carrying amount of liability	213,121,000	205,182,000
Senior Credit Facility
Debt Instrument [Line Items]
Line of credit facility outstanding	266,900,000	186,900,000
Weighted average interest rate on debt	1.70%	2.00%
Available borrowings under senior secured revolving credit facility	483,100,000
Fair value of outstanding borrowings	248,200,000
Senior Credit Facility | August 2010 Amendment
Debt Instrument [Line Items]
Senior credit facility, maximum borrowing capacity				450,000,000
Line of credit facility, expiration date				Aug. 10, 2015
Senior Credit Facility | June 2011 Amendment
Debt Instrument [Line Items]
Senior credit facility, maximum borrowing capacity				600,000,000
Reallocated term loan				150,000,000
Senior credit facility, additional commitments				200,000,000
Line of credit facility, expiration date				Jun. 08, 2016
Senior Credit Facility | May 2012 Amendment
Debt Instrument [Line Items]
Capitalized incremental financing costs							400,000
Senior Credit Facility | May 2012 Amendment | Minimum
Debt Instrument [Line Items]
Maximum consolidated total leverage ratio (net debt to consolidated EBITDA)							1
Senior Credit Facility | May 2012 Amendment | Maximum
Debt Instrument [Line Items]
Maximum consolidated total leverage ratio (net debt to consolidated EBITDA)							3.75
Senior Credit Facility | June 2013 Amendment
Debt Instrument [Line Items]
Capitalized incremental financing costs								1,100,000
Senior Credit Facility | June 2013 Amendment | Maximum
Debt Instrument [Line Items]
Maximum consolidated total leverage ratio (net debt to consolidated EBITDA)								3.75
July 2014 Amendment
Debt Instrument [Line Items]
Senior credit facility, maximum borrowing capacity					900,000,000
Capitalized incremental financing costs					3,200,000
Cash balance threshold above which excess amount is not subject to any restriction of use or investment					40,000,000.0
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
2016 Convertible Senior Notes
Debt Instrument [Line Items]
Fair value of outstanding borrowings	254,000,000
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
Debt Instrument, Interest Rate, Effective Percentage									5.60%
Carrying amount of liability	213,100,000	205,200,000
Unamortized discount	16,900,000	24,800,000
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%
Earliest conversion date	June 15, 2016
Strike price of the call transaction (in dollars per share)	$ 57.44
Strike price of warrant transactions (in dollars per share)	$ 70.05
2012 Senior Convertible Notes
Debt Instrument [Line Items]
Principal amount outstanding										165,000,000
Interest rate on debt										2.375%
Portion of the debt proceeds that was classified as equity at the time of the offering										30,600,000
Debt Instrument, Interest Rate, Effective Percentage										6.80%
Cost of call transactions										30,400,000
Proceeds from warrant transactions										12,200,000
Bond hedge contract termination, trading day period (in days)						100 days
Bond hedge contract termination, commencement period (in days)						90 days
Leverage Ratio June 21, 2013 through June 30, 2014 | Senior Credit Facility | June 2013 Amendment | Maximum
Debt Instrument [Line Items]
Maximum consolidated total leverage ratio (net debt to consolidated EBITDA)								4.25
Leverage Ratio July 01, 2014 through March 31, 2015 | Senior Credit Facility | June 2013 Amendment | Maximum
Debt Instrument [Line Items]
Maximum consolidated total leverage ratio (net debt to consolidated EBITDA)								4.00
Revolving Credit Facility | July 2014 Amendment
Debt Instrument [Line Items]
Senior credit facility, maximum borrowing capacity					750,000,000
Proceeds from Lines of Credit					272,000,000
Standby Letters of Credit | July 2014 Amendment
Debt Instrument [Line Items]
Senior credit facility, maximum borrowing capacity					60,000,000.0
Swingline Loan | July 2014 Amendment
Debt Instrument [Line Items]
Senior credit facility, maximum borrowing capacity					60,000,000.0
Term Loan
Debt Instrument [Line Items]
Weighted average interest rate on debt	1.70%
Term loan, amount outstanding	150,000,000
Fair value of outstanding borrowings	140,300,000
Term Loan | July 2014 Amendment
Debt Instrument [Line Items]
Senior credit facility, maximum borrowing capacity					$ 150,000,000
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%
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%