SUBSEQUENT EVENTS (Details) (USD $)	0 Months Ended	6 Months Ended	0 Months Ended				0 Months Ended
	Jun. 04, 2013 Convertible Subordinated Notes Due 2015	Jun. 30, 2013 Convertible Subordinated Notes Due 2015	Jul. 05, 2013 Subsequent events Convertible Subordinated Notes Due 2015	Jul. 03, 2013 Subsequent events Convertible Subordinated Notes Due 2015	Jul. 03, 2013 Subsequent events Convertible Subordinated Notes Due 2015	Sep. 30, 2013 Subsequent events Convertible Subordinated Notes Due 2015	Jul. 30, 2013 Subsequent events Common stock Future Sale of Stock GSK
Subsequent events
Percentage of principal amount at which the entity may redeem some or all notes		100.00%	100.00%
Conversion rate of shares		0.0386548			0.0386548
Conversion price of convertible notes into common stock (in dollars per share)		$ 25.87		$ 25.87	$ 25.87
Agreement to issue stock, number of shares							3,064,407
Agreement to issue stock in private placement, price per shares (in dollars per share)							$ 36.50
Agreement to issue stock in private placement, aggregate purchase price							$ 111,900,000
Principal amount of debt converted	172,500,000	40,000
Number of common shares issued upon debt conversion		1,546		6,667,932	6,666,386
Unamortized issuance costs		1,300,000				1,300,000
Debt redeemed for cash				$ 0