Investment Securities - Carrying Amounts and Fair Values of Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 123,494	$ 89,351
Gross Unrealized Gains	1,430	2,411
Gross Unrealized Losses	1,798	124
Fair Value	123,126	91,638
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	23,522	18,731
Gross Unrealized Gains	572	846
Gross Unrealized Losses	222	1
Fair Value	23,872	19,576
U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	52,384	21,689
Gross Unrealized Gains	243	485
Gross Unrealized Losses	946
Fair Value	51,681	22,174
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	40,235	40,766
Gross Unrealized Gains	229	379
Gross Unrealized Losses	630	123
Fair Value	39,834	41,022
State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,353	8,165
Gross Unrealized Gains	386	701
Gross Unrealized Losses
Fair Value	$ 7,739	$ 8,866