Investment Securities - Estimated fair values of investment securities (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Total investment securities available for sale, Amortized cost	$ 104,530	$ 85,146
Total investment securities available for sale,Gross unrealized gains	3	155
Total investment securities available for sale, Gross unrealized losses	0	3
Total investment securities available for sale,Estimated fair value	102,737	85,298
Total investment securities held-to-maturity, Amortized cost	792	903
Total investment securities held-to-maturity,Gross unrealized gains	45	54
Total investment securities held-to-maturity, Gross unrealized losses	0	0
Total investment securities held-to-maturity, Estimated fair value	837	957
U.S. Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Total investment securities available for sale, Amortized cost	104,419	83,956
Total investment securities available for sale,Gross unrealized gains	0	118
Total investment securities available for sale, Gross unrealized losses	1,796	3
Total investment securities available for sale,Estimated fair value	102,623	84,071
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total investment securities available for sale, Amortized cost	44	44
Total investment securities available for sale,Gross unrealized gains	0	0
Total investment securities available for sale, Gross unrealized losses	0	0
Total investment securities available for sale,Estimated fair value	44	44
Total investment securities held-to-maturity, Amortized cost	0
Total investment securities held-to-maturity, Estimated fair value	0
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total investment securities available for sale, Amortized cost	67	1,146
Total investment securities available for sale,Gross unrealized gains	3	37
Total investment securities available for sale, Gross unrealized losses	0	0
Total investment securities available for sale,Estimated fair value	70	1,183
Total investment securities held-to-maturity, Amortized cost	792	903
Total investment securities held-to-maturity,Gross unrealized gains	45	54
Total investment securities held-to-maturity, Gross unrealized losses	0	0
Total investment securities held-to-maturity, Estimated fair value	$ 837	$ 957