DEBT (Narrative) (Details) (USD $)							12 Months Ended		12 Months Ended		12 Months Ended							12 Months Ended			1 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Senior Credit Facility	Dec. 31, 2011 Senior Credit Facility	Dec. 31, 2012 Senior Credit Facility Option ii, X	Dec. 31, 2012 Senior Credit Facility Option ii, Z	Dec. 31, 2012 Senior Credit Facility Minimum	Dec. 31, 2012 Senior Credit Facility Minimum Option i	Dec. 31, 2012 Senior Credit Facility Maximum	Dec. 31, 2012 Senior Credit Facility Maximum Option i	Dec. 31, 2012 Senior Credit Facility August 2010 Amendment	Dec. 31, 2012 Senior Credit Facility June 2011 Amendment	Dec. 31, 2010 Senior Credit Facility June 2011 Amendment	Dec. 31, 2012 Senior Credit Facility June 2011 Amendment Maximum	Dec. 31, 2012 Senior Credit Facility May 2012 Amendment	May 31, 2012 Senior Credit Facility May 2012 Amendment Minimum	May 31, 2012 Senior Credit Facility May 2012 Amendment Maximum	Dec. 31, 2012 2016 Convertible Senior Notes	Dec. 31, 2011 2016 Convertible Senior Notes	Jun. 15, 2011 2016 Convertible Senior Notes	Jun. 11, 2007 2012 Senior Convertible Notes	Dec. 31, 2012 2012 Senior Convertible Notes
Debt Instrument [Line Items]
Senior credit facility, maximum borrowing capacity													$ 450,000,000	$ 600,000,000
Reallocated term loan													150,000,000
Senior credit facility, additional commitments												200,000,000
Line of credit facility, expiration date											Aug. 10, 2015	Jun. 08, 2016
Maximum consolidated total leverage ratio (net debt to consolidated EBITDA)																1	3.75
Capitalized incremental financing costs															400,000
Interest rates available to the Company at its option					0.50%	1.00%		1.00%		1.75%
Cash balance threshold above which excess amount is not subject to any restriction of use or investment			40,000,000
Line of credit, commitment fee percentage							0.15%		0.30%
Line of credit facility outstanding			321,900,000	179,700,000
Weighted average interest rate on debt			1.80%	2.00%
Available borrowings under senior secured revolving credit facility			278,100,000
Fair value of outstanding borrowings			310,300,000															232,900,000
Principal amount outstanding																		230,000,000	230,000,000	230,000,000	165,000,000
Interest rate on debt																				1.625%	2.375%
Portion of the debt proceeds that was classified as equity at the time of the offering																				43,200,000	30,600,000
Effective interest rate implicit in the liability component																		5.60%			6.80%
Carrying amount of liability	197,672,000	352,576,000																197,700,000	190,600,000
Unamortized discount																		32,300,000	39,400,000
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
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