Total Compensation Cost from Share-Based Payments (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation cost	$ 7,675	$ 4,836	$ 4,355
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation cost	3,782	2,444	2,123
General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation cost	3,893	2,392	2,232
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation cost	2,893	1,879	3,068
Stock and Stock Units Grants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation cost	4,601	2,834	1,096
Employee Stock Purchase Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation cost	$ 181	$ 123	$ 191