LONG-TERM DEBT (Details) (USD $)	3 Months Ended				0 Months Ended	1 Months Ended	3 Months Ended	9 Months Ended				1 Months Ended	3 Months Ended	9 Months Ended
	Mar. 31, 2013	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Privately-negotiated capped call option Item	Jul. 03, 2013 Convertible Subordinated Notes Due 2015	Jan. 31, 2008 Convertible Subordinated Notes Due 2015	Sep. 30, 2012 Convertible Subordinated Notes Due 2015	Sep. 30, 2013 Convertible Subordinated Notes Due 2015	Sep. 30, 2012 Convertible Subordinated Notes Due 2015	Jun. 04, 2013 Convertible Subordinated Notes Due 2015	Dec. 31, 2012 Convertible Subordinated Notes Due 2015	Jan. 31, 2013 Convertible Subordinated Notes Due 2023	Sep. 30, 2013 Convertible Subordinated Notes Due 2023	Sep. 30, 2013 Convertible Subordinated Notes Due 2023	Sep. 30, 2013 Convertible Subordinated Notes Due 2023 Privately-negotiated capped call option	Sep. 30, 2013 Convertible Subordinated Notes Due 2023 Stock prices below $27.79 per share Minimum	Sep. 30, 2013 Convertible Subordinated Notes Due 2023 Stock prices above $38.00 per share	Sep. 30, 2013 Convertible Subordinated Notes Due 2023 Stock prices above $38.00 per share Maximum
Debt disclosures
Convertible subordinated notes		$ 287,500,000	$ 172,500,000								$ 172,500,000		$ 287,500,000	$ 287,500,000
Loan amount						172,500,000						287,500,000
Interest rate (as a percent)						3.00%				3.00%		2.125%	2.125%	2.125%
Proceeds from issuance of debt, net of issuance costs						166,700,000						281,200,000
Payments on capped call option transactions															36,800,000
Number of derivative instruments purchased				2
Unamortized issuance costs								1,300,000					5,900,000	5,900,000
Amortization expense							200,000	400,000	600,000				200,000	400,000
Initial conversion rate of shares								0.0386548						0.0359903
Initial conversion price of convertible notes into common stock (in dollars per share)								$ 25.87					$ 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%
Principal amount of debt converted					172,500,000
Number of common shares issued upon debt conversion					6,667,932
Debt redeemed for cash								0
Strike price for the underlying number of shares (in dollars per share)															$ 27.79		$ 38
Cap price for the underlying number of shares (in dollars per share)															$ 38
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