Summary of Restructuring Related Obligations (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]
Balance at beginning of period	$ 64	$ 529
Termination benefits accrued	1,463	2,081	529
Employee, office and other costs accrued	888	6,119
Cash payments	(1,839)	(8,665)
Balance at end of period	$ 576	$ 64	$ 529