Summary of Restructuring Charges (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 2,351	$ 8,200	$ 529
Termination benefits
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,463	2,081	529
Employee and office relocation costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	322	1,597
Other incremental costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges		1,022
Facility lease-related charges
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 566	$ 3,500