Investment Securities - Gross Gains (Losses) Realized on Sales, Maturities and Other Securities Transactions Included in Earnings (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Investments Debt And Equity Securities [Abstract]
Gross gains, sales transactions									$ 14,098	$ 6,621	$ 31,456
Gross losses, sales transactions									(44)	(1,050)
Gains on sales transactions, net									14,054	5,571	31,456
Gross gains, maturities and other securities transactions									662	2,327	623
Gross losses, maturities and other securities transactions									(38)	(5,311)	(11)
Gains (losses) on maturities and other securities transactions, net									624	(2,984)	612
Gains on securities transactions, net	$ 10,670	$ 9	$ 41	$ 3,958	$ 44	$ 1,496	$ 1,204	$ (157)	$ 14,678	$ 2,587	$ 32,068