Investment Securities - Fair value of investment securities by contractual term maturity (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available for sale due in one year or less, Amortized cost	$ 0
Available for sale due after one year through five years, Amortized cost	98,420
Available for sale due after five years through ten years, Amortized cost	5,999
Available for sale due after ten years, Amortized cost	0
Total investment securities available for sale, Amortized cost	104,530	85,146
Available for sale due in one year or less, Estimated fair value	0
Available for sale due after one year through five years, Estimated fair value	96,851
Available for sale due after five years through ten years, Estimated fair value	5,772
Available for sale due after ten years, Estimated fair value	0
Total investment securities available for sale, Estimated fair value	102,737	85,298
Held to maturity Due in one year or less, Amortized cost	0
Held to maturity Due after one year through five years, Amortized cost	0
Held to maturity Due after five years through ten years, Amortized cost	0
Held to maturity Due after ten years, Amortized cost	0
Total investment securities held-to-maturity, Amortized cost	792	903
Due in one year or less, Estimated fair value	0
Due after one year through five years, Estimated fair value	0
Due after five years through ten years, Estimated fair value	0
Due after ten years, Estimated fair value	0
Total investment securities held to maturity, Estimated fair value	837	957
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total investment securities available for sale, Amortized cost	104,419
Total investment securities available for sale, Estimated fair value	102,623
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, Estimated fair value	70	1,183
Total investment securities held-to-maturity, Amortized cost	792	903
Total investment securities held to maturity, Estimated fair value	837	957
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, Estimated fair value	44	44
Total investment securities held-to-maturity, Amortized cost	0
Total investment securities held to maturity, Estimated fair value	$ 0