Restructuring Charges - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended
	Feb. 10, 2011 Employee	Dec. 31, 2011
Restructuring Cost and Reserve [Line Items]
Percentage of workforce reduction	41.00%
Number of employees eliminated	257
Restructuring charges	$ 6,700,000
Restructuring charges, net of tax		6,300,000
Workforce Reduction
Restructuring Cost and Reserve [Line Items]
Restructuring liability	6,659,000	67,000
Research And Development
Restructuring Cost and Reserve [Line Items]
Restructuring charges, net of tax		4,700,000
General and Administrative
Restructuring Cost and Reserve [Line Items]
Restructuring charges, net of tax		$ 1,600,000