Stock-Based Compensation Expense on All Employee and Non-Employee Awards (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended		121 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 809	$ 1,191	$ 2,482	$ 3,482	$ 22,663
Research and Development Expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	119	363	511	1,305
General and Administrative Expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 690	$ 828	$ 1,971	$ 2,177