Changes in Level 3 Assets Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended			9 Months Ended									9 Months Ended
	Sep. 30, 2012 Available for sale securities		Sep. 30, 2011 Available for sale securities	Sep. 30, 2012 Available for sale securities		Sep. 30, 2011 Available for sale securities		Sep. 30, 2011 Available for sale securities Residential mortgage-backed securities	Sep. 30, 2011 Available for sale securities Trust preferred securities	Sep. 30, 2011 Available for sale securities Corporate and other debt securities	Sep. 30, 2011 Available for sale securities Equity securities	Dec. 31, 2010 Trading securities	Sep. 30, 2011 Trading securities Trust preferred securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Balance, beginning of the period	$ 89,091		$ 51,218	$ 77,311		$ 138,655						$ 21,903
Transfers out of Level 3								(44,771)	(17,397)	(12,914)	(9,353)		(21,903)
Total net (losses) gains for the period included in, net income	(4,697)			(5,247)		(825)
Total net (losses) gains for the period included in, other comprehensive income	(150)		(489)	18,804		1,723
Settlements	(1,965)		(2,565)	(8,589)		(6,954)
Balance, end of the period	82,279		48,164	82,279		48,164						21,903
Change in unrealized losses for the period included in earnings for assets held at the end of the reporting period	$ (4,697)	[1]		$ (5,247)	[1]	$ (825)	[1]

[1] Represents the net impairment losses on securities recognized in earnings for the period.