Investment Securities - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Percentage of debt securities considered to be of investment-grade	95.00%		95.00%
Percentage of tax-exempt municipal securities classified as pre-refunded	5.00%		5.00%
General obligation bonds as percentage of tax-exempt municipal securities that were not pre-refunded			38.00%
Special revenue bonds as percentage of tax exempt municipal securities that were not pre-refunded			62.00%
Maximum percentage of any general obligation bonds in one state			11.00%
Percentage of tax-exempt securities insured by bond insurers	17.00%		17.00%
Residential and commercial mortgage-backed securities, percentage of collateral consisting of prime loans	99.00%		99.00%
Percentage of corporate securities associated with financial services industry	21.00%		21.00%		23.00%
Other-than-temporary impairments	$ 0	$ 0	$ 0	$ 0