Stock-Based Compensation Expense on All Employee and Non-Employee Awards (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		118 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 132	$ 1,078	$ 1,673	$ 2,290	$ 21,854
Research and Development Expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	(145)	426	392	942
General and Administrative Expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 277	$ 652	$ 1,281	$ 1,348