Fair Value Measurement of Assets and Liabilities - Changes in Level 3 Assets Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended				12 Months Ended
	Dec. 31, 2011	Dec. 31, 2012 Trading Securities [Member]		Dec. 31, 2010 Trading Securities [Member]	Dec. 31, 2012 Trading Securities [Member] Residential mortgage-backed securities [Member]	Dec. 31, 2012 Trading Securities [Member] Trust preferred securities [Member]	Dec. 31, 2011 Trading Securities [Member] Trust preferred securities [Member]	Dec. 31, 2012 Trading Securities [Member] Corporate and other debt securities [Member]	Dec. 31, 2012 Trading Securities [Member] Equity securities [Member]	Dec. 31, 2012 Available For Sale Securities [Member]		Dec. 31, 2011 Available For Sale Securities [Member]		Dec. 31, 2012 Available For Sale Securities [Member] Residential mortgage-backed securities [Member]	Dec. 31, 2011 Available For Sale Securities [Member] Residential mortgage-backed securities [Member]	Dec. 31, 2012 Available For Sale Securities [Member] Trust preferred securities [Member]	Dec. 31, 2011 Available For Sale Securities [Member] Trust preferred securities [Member]	Dec. 31, 2012 Available For Sale Securities [Member] Corporate and other debt securities [Member]	Dec. 31, 2011 Available For Sale Securities [Member] Corporate and other debt securities [Member]	Dec. 31, 2012 Available For Sale Securities [Member] Equity securities [Member]	Dec. 31, 2011 Available For Sale Securities [Member] Equity securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, beginning of the period				$ 21,903						$ 77,311		$ 138,655
Transfers into Level 3															8,798
Transfers out of Level 3							(21,903)								(44,771)		(17,397)		(12,914)		(9,353)
Transfers from held-to-maturity	18,300		[1]								[1]	23,452	[1]
Total net (losses) gains for the period included in net income										(5,247)		(1,654)
Total net (losses) gains for the period included in Other comprehensive income										18,482		765
Sales										(9,146)
Settlements										(9,726)		(8,270)
Balance, end of the period				21,903						71,674		77,311
Change in unrealized losses for the period included in earnings for assets held at year end			[2]							$ (5,247)	[2]	$ (19,968)	[2],[3]

[1] Represents impaired trust preferred securities issued by one bank holding company transferred at fair value from held-to-maturity to available-for-sale at December 31, 2011.

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

[3] Includes $18.3 million related to trust preferred securities transferred from held-to-maturity at December 31, 2011.