Investment Securities - Additional Information (Detail) (USD $)	9 Months Ended	12 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2014 Securities	Dec. 31, 2013 Securities	Sep. 30, 2014 Mortgage-backed securities Non-Agency Alt-A residential	Sep. 30, 2014 Debt Securities	Sep. 30, 2013 Debt Securities	Sep. 30, 2014 Debt Securities	Sep. 30, 2013 Debt Securities	Sep. 30, 2014 Non Agency Mortgage Backed Securities	Sep. 30, 2013 Non Agency Mortgage Backed Securities	Sep. 30, 2014 Non Agency Mortgage Backed Securities	Sep. 30, 2013 Non Agency Mortgage Backed Securities	Sep. 30, 2014 Equity Securities	Sep. 30, 2013 Equity Securities	Sep. 30, 2014 Equity Securities	Sep. 30, 2013 Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity securities in continuous unrealized loss position		$ 0
Number of securities in an unrealized loss position	114	219
Percentage of combined depreciation of the combined reported value of the aggregate securities portfolio	3.57%	5.06%
Carrying value of securities pledged	260,450,000	284,770,000
OTTI charges incurred				$ 0	$ 0	$ 0	$ 0	$ 219,000	$ 0	$ 705,000	$ 0	$ 0	$ 0	$ 32,000	$ 0
Voluntary constant prepayment rate			2.50%
Constant default rate scenario			13.00%
Severity rate			45.00%
Reduced severity rate	10.00%
Severity rate reduction period	27 months