Fair Value - Estimated Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Fair Value Of Other Financial Instrument [Line Items]
Cash and cash equivalents	$ 28,701
Securities available for sale	389,885	346,542
Interest receivable	4,520
Bank-owned life insurance	15,621	15,038
Deposits	1,046,165
Federal funds and overnight funds purchased	11,570
Federal Home Loan Bank borrowings	119,517
Junior subordinated debentures	2,193
Carrying Amount [Member]
Fair Value Of Other Financial Instrument [Line Items]
Cash and cash equivalents	28,701	19,859
Securities available for sale	389,885	346,542
Loans held-for-sale		1,058
Loans	870,416	820,152
Interest receivable	4,520	4,725
Federal Home Loan Bank stock	10,462	10,652
Bank-owned life insurance	15,621	15,038
Deposits	1,046,154	965,254
Federal funds and overnight funds purchased	11,570	12,300
Federal Home Loan Bank borrowings	118,000	101,500
Junior subordinated debentures	8,248	8,248
Accrued interest payable	218	264
Fair Value [Member]
Fair Value Of Other Financial Instrument [Line Items]
Cash and cash equivalents	28,701	19,859
Securities available for sale	389,885	346,542
Loans held-for-sale		1,058
Loans	871,802	814,882
Interest receivable	4,520	4,725
Federal Home Loan Bank stock	10,462	10,652
Bank-owned life insurance	15,621	15,038
Deposits	1,046,165	965,724
Federal funds and overnight funds purchased	11,570	12,300
Federal Home Loan Bank borrowings	119,517	103,884
Junior subordinated debentures	2,193	2,039
Accrued interest payable	$ 218	$ 264