LONG-TERM DEBT (Details) (USD $)	3 Months Ended				0 Months Ended		1 Months Ended	3 Months Ended		6 Months Ended			1 Months Ended	3 Months Ended	6 Months Ended
	Mar. 31, 2013	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Privately-negotiated capped call option Item	Jun. 04, 2013 Convertible Subordinated Notes Due 2015	Jan. 15, 2012 Convertible Subordinated Notes Due 2015	Jan. 31, 2008 Convertible Subordinated Notes Due 2015	Jun. 30, 2013 Convertible Subordinated Notes Due 2015	Jun. 30, 2012 Convertible Subordinated Notes Due 2015	Jun. 30, 2013 Convertible Subordinated Notes Due 2015	Jun. 30, 2012 Convertible Subordinated Notes Due 2015	Dec. 31, 2012 Convertible Subordinated Notes Due 2015	Jan. 31, 2013 Convertible Subordinated Notes Due 2023	Jun. 30, 2013 Convertible Subordinated Notes Due 2023	Jun. 30, 2013 Convertible Subordinated Notes Due 2023	Jun. 30, 2013 Convertible Subordinated Notes Due 2023 Privately-negotiated capped call option	Jun. 30, 2013 Convertible Subordinated Notes Due 2023 Stock prices below $27.79 per share Minimum	Jun. 30, 2013 Convertible Subordinated Notes Due 2023 Stock prices above $38.00 per share	Jun. 30, 2013 Convertible Subordinated Notes Due 2023 Stock prices above $38.00 per share Maximum
Debt disclosures
Convertible subordinated notes		$ 459,960,000	$ 172,500,000					$ 172,460,000		$ 172,460,000		$ 172,500,000		$ 287,500,000	$ 287,500,000
Loan amount							172,500,000						287,500,000
Net proceeds from issuance of debt							166,700,000						281,200,000
Payments on capped call option transactions																36,800,000
Number of derivative instruments purchased				2
Interest rate (as a percent)					3.00%		3.00%	3.00%		3.00%			2.125%	2.125%	2.125%
Unamortized issuance costs								1,300,000		1,300,000				6,000,000	6,000,000
Amortization expense								200,000	200,000	400,000	400,000			200,000	300,000
Initial conversion rate of shares										0.0386548					0.0359903
Initial conversion price of convertible notes into common stock (in dollars per share)								$ 25.87		$ 25.87				$ 27.79	$ 27.79
Percentage of principal amount at which the entity may be forced to redeem some or all notes as a result of a fundamental change (as defined)										100.00%					100.00%
Percentage of principal amount at which the entity may redeem some or all notes										100.00%
Percentage of closing sales price of the entity's common stock the conversion price must exceed in order for the notes to be convertible						130.00%
Number of days within 30 consecutive trading days in which the closing price of the entity's common stock must exceed the conversion price for the notes to be redeemable										20 days
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the conversion price for at least 20 days in order for the notes to be redeemable										30 days
Strike price for the underlying number of shares (in dollars per share)																$ 27.79		$ 38.00
Cap price for the underlying number of shares (in dollars per share)																$ 38.00
Net shares settlement payable to the entity																	0		2,779,659
Incremental anti-dilutive benefit																		0
Change in fair value between the trade dates and the date at which the capped call derivative assets were reclassified to stockholders' equity	1,400,000
Principal amount of debt converted					$ 172,500,000					$ 40,000
Number of common shares issued upon debt conversion										1,546