Subsequent Events (Details) (Subsequent events, USD $)	0 Months Ended
	Jan. 24, 2013 Maximum	Jan. 24, 2013 Minimum	Feb. 15, 2013 Common stock Future Sale of Stock GSK	Jan. 24, 2013 Privately-negotiated capped call option	Jan. 24, 2013 Stock prices below $27.79 per share Common stock	Jan. 24, 2013 Stock prices above $38.00 per share Common stock	Jan. 24, 2013 2.125% convertible subordinated notes	Jan. 24, 2013 2.125% convertible subordinated notes Common stock
Subsequent event
Loan amount							$ 287,500,000
Interest rate (as a percent)							2.125%
Full exercise of the underwriters' over-allotment option principal amount							37,500,000
Proceeds from issuance of debt, net of issuance costs							244,400,000
Conversion rate, number of shares to be issued per $1000 of principal amount of notes								35.9903
Principal amount used for debt instrument conversion ratio								1,000
Initial conversion price of convertible notes into common stock (in dollars per share)								$ 27.79
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	2,779,659	0
Stock price (in dollars per share)			$ 22.03
Aggregate cost of the capped call options				36,800,000
Agreement to issue stock, number of shares			116,527
Agreement to issue stock in private placement, aggregate purchase price			$ 2,600,000