Securities - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Collateral Backed Securities Issued by Private Enterprises [Member]	Sep. 30, 2013 Mortgage Backed Securities and Collateralized Mortgage Obligations of US Government Sponsored Entities [Member]	Sep. 30, 2013 Collateralized Mortgage Obligations of U.S. Government Sponsored Entities [Member]	Dec. 31, 2012 Collateralized Mortgage Obligations of U.S. Government Sponsored Entities [Member]	Sep. 30, 2013 Private Collateralized Mortgage Obligations [Member]	Dec. 31, 2012 Private Collateralized Mortgage Obligations [Member]	Sep. 30, 2013 Carrying Amount [Member] Collateralized Mortgage Obligations of U.S. Government Sponsored Entities [Member]	Sep. 30, 2013 Carrying Amount [Member] Private Collateralized Mortgage Obligations [Member]	Sep. 30, 2013 Fair Value [Member] Collateralized Mortgage Obligations of U.S. Government Sponsored Entities [Member]	Sep. 30, 2013 Fair Value [Member] Private Collateralized Mortgage Obligations [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Proceeds from sale of securities	$ 67,330,000	$ 248,509,000
Gains from sale of securities	792,000	7,251,000
Gross losses	373,000	214,000
Securities									71,680,000	160,751,000	71,680,000	160,751,000
Aggregate losses			900,000	13,800,000	10,144,000	994,000	297,000	530,000
Fair Value, Total			71,500,000	410,600,000	328,619,000	154,650,000	42,432,000	39,190,000
Collateral underlying mortgage investments terms	30- and 15-year fixed and adjustable rate mortgage
Federal Home Loan Bank and Federal Reserve Bank stock	11,300,000
Fair value of cost method investment securities	$ 11,300,000