Securities - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Proceeds from sales of securities available for sale	$ 77,583,000	$ 333,912,000
Gross realized gains from securities	1,500,000	5,900,000
Gross realized losses from securities	11,000	37,000
Sales of securities held to maturity	0	0
Unrealized gains on trading securities	300,000	200,000
Fair value of marketable securities	17,400,000		16,600,000
Fair value of non-marketable securities	6,300,000		4,700,000
Us Government and Other Public Deposit [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Pledged securities for deposits	5,400,000,000		5,900,000,000
Federal Reserve Discount Window [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Pledged securities for deposits	$ 1,600,000,000		$ 1,700,000,000