Description Of Business (Detail) (USD $)	3 Months Ended		6 Months Ended			3 Months Ended			6 Months Ended		3 Months Ended			6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011	Jun. 30, 2012 Collaborative Arrangement [Member] Astellas [Member]	Jun. 30, 2011 Collaborative Arrangement [Member] Astellas [Member]	Dec. 31, 2009 Collaborative Arrangement [Member] Astellas [Member]	Jun. 30, 2012 Collaborative Arrangement [Member] Astellas [Member]	Jun. 30, 2011 Collaborative Arrangement [Member] Astellas [Member]	Jun. 30, 2012 Collaborative Arrangement [Member] Pfizer [Member]	Jun. 30, 2011 Collaborative Arrangement [Member] Pfizer [Member]	Dec. 31, 2008 Collaborative Arrangement [Member] Pfizer [Member]	Jun. 30, 2012 Collaborative Arrangement [Member] Pfizer [Member]	Jun. 30, 2011 Collaborative Arrangement [Member] Pfizer [Member]	Jun. 30, 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	$ 255,351,000		$ 255,351,000		$ 250,291,000
Net income	(5,500,000)	(9,474,000)	(5,060,000)	(17,926,000)
Negative cash flow from operations			55,761,000	31,159,000
Cash, cash equivalents, and short-term investments	344,500,000		344,500,000
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
Non-refundable up-front cash payment								110,000,000					225,000,000
Development milestone payments									13,000,000
Development and commercialization cost-sharing payments						$ 14,200,000	$ 11,800,000		$ 27,500,000	$ 21,600,000	$ 400,000	$ 3,000,000		$ 1,700,000	$ 7,900,000
Percentage of sales and medical affairs			50.00%						50.00%