Convertible Senior Subordinated Notes due 2015 (Details) (USD $)			1 Months Ended	3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2010 Convertible Senior Subordinated Notes 3.35 Percent Due 2015 D Y	Mar. 31, 2012 Convertible Senior Subordinated Notes 3.35 Percent Due 2015
Convertible Senior Subordinated Notes and Collaborator Loan
Convertible senior subordinated notes	$ 400,000,000	$ 400,000,000	$ 400,000,000	$ 400,000,000
Interest rate (as a percent)			3.35%	3.35%
Net proceeds from convertible debt offering			391,600,000
Underwriting discount			8,000,000
Debt issuance costs			400,000
Conversion price (in dollars per share)			$ 48.83
Original conversion rate, number of shares to be issued per $1000 of principal (in shares)			20.4794
Convertible debt principal amount, basis for exchange			$ 1,000
Percent closing price needs to exceed the conversion price for at least 20 trading days within 30 consecutive trading days for provisional redemption (as a percent)			130.00%
Minimum number of days within 30 consecutive trading days the closing price needs to exceed the conversion price for provisional redemption (in days)			20
Total consecutive trading days during which the closing price must exceed the conversion price for at least 20 trading days for provisional redemption (in days)			30
Percentage of principal amount used in computation of provisional redemption price (as a percent)			100.00%
Total interest payments on notes being provisionally redeemed equal to interest for specified number of years (in years)			3