Description Of Business (Details) (USD $)	3 Months Ended			3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011	Mar. 31, 2012 Collaboration Arrangement [Member] Astellas [Member]	Jun. 30, 2011 Collaboration Arrangement [Member] Astellas [Member]	Mar. 31, 2011 Collaboration Arrangement [Member] Astellas [Member]	Dec. 31, 2010 Collaboration Arrangement [Member] Astellas [Member]	Dec. 31, 2009 Collaboration Arrangement [Member] Astellas [Member]	Mar. 31, 2012 Collaboration Arrangement [Member] Pfizer [Member]	Mar. 31, 2011 Collaboration Arrangement [Member] Pfizer [Member]	Dec. 31, 2008 Collaboration Arrangement [Member] Pfizer [Member]	Mar. 31, 2012 2.625% Convertible Senior Notes Due 2017 [Member]	Mar. 19, 2012 2.625% Convertible Senior Notes Due 2017 [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Cumulative net losses	$ 249,851,000		$ 250,291,000
Net income	440,000	(8,452,000)
Development milestone payments					3,000,000		10,000,000
Non-refundable up-front cash payment								110,000,000			225,000,000
Development and commercialization cost-sharing payments				13,300,000		9,800,000			1,300,000	4,900,000
Percentage of sales and medical affairs	50.00%			50.00%
Cash, cash equivalents, and short-term investments	380,100,000
Convertible Notes, aggregate principal amount	258,800,000											258,800,000	258,800,000
Debt instrument, interest rate												2.625%
Cash proceeds from the sale of the Convertible Notes	250,987,000											251,000,000
Underwriter discounts												$ 7,800,000