Fair Value Disclosures - Assets, Liabilities and Off-balance Sheet Items Not Measured at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Assets:
Held-to-maturity securities	$ 57,101	$ 66,853
Deposits:
Time deposits	261,176	270,789
Fair Value [Member]
Assets:
Cash and short-term interest-earning assets	68,408	69,169
Held-to-maturity securities	57,101	66,853
Loans held for sale	2,199	2,267
Net loans and leases held for investment	1,526,454	1,477,945
Mortgage servicing rights	7,337	7,188
Other real estate owned	955	1,650
Total assets	1,662,454	1,625,072
Deposits:
Demand and savings deposits, non-maturity	1,598,967	1,573,709
Time deposits	263,317	268,909
Total deposits	1,862,284	1,842,618
Short-term borrowings	34,728	35,687
Total liabilities	1,897,012	1,878,305
Off-Balance-Sheet:
Commitments to extend credit	(1,408)	(1,357)
Fair Value [Member] | Level 1 [Member]
Assets:
Cash and short-term interest-earning assets	68,408	69,169
Held-to-maturity securities	0	0
Loans held for sale	0	0
Net loans and leases held for investment	0	0
Mortgage servicing rights	0	0
Other real estate owned	0	0
Total assets	68,408	69,169
Deposits:
Demand and savings deposits, non-maturity	1,598,967	1,573,709
Time deposits	0	0
Total deposits	1,598,967	1,573,709
Short-term borrowings	0	0
Total liabilities	1,598,967	1,573,709
Off-Balance-Sheet:
Commitments to extend credit	0	0
Fair Value [Member] | Level 2 [Member]
Assets:
Cash and short-term interest-earning assets	0	0
Held-to-maturity securities	57,101	66,853
Loans held for sale	2,199	2,267
Net loans and leases held for investment	0	0
Mortgage servicing rights	0	7,188
Other real estate owned	955	1,650
Total assets	60,255	77,958
Deposits:
Demand and savings deposits, non-maturity	0	0
Time deposits	263,317	268,909
Total deposits	263,317	268,909
Short-term borrowings	34,728	35,687
Total liabilities	298,045	304,596
Off-Balance-Sheet:
Commitments to extend credit	(1,408)	(1,357)
Fair Value [Member] | Level 3 [Member]
Assets:
Cash and short-term interest-earning assets	0	0
Held-to-maturity securities	0	0
Loans held for sale	0	0
Net loans and leases held for investment	1,526,454	1,477,945
Mortgage servicing rights	7,337	0
Other real estate owned	0	0
Total assets	1,533,791	1,477,945
Deposits:
Demand and savings deposits, non-maturity	0	0
Time deposits	0	0
Total deposits	0	0
Short-term borrowings	0	0
Total liabilities	0	0
Off-Balance-Sheet:
Commitments to extend credit	0	0
Carrying Amount [Member]
Assets:
Cash and short-term interest-earning assets	68,408	69,169
Held-to-maturity securities	56,476	66,003
Loans held for sale	2,156	2,267
Net loans and leases held for investment	1,518,037	1,461,620
Mortgage servicing rights	5,425	5,519
Other real estate owned	955	1,650
Total assets	1,651,457	1,606,228
Deposits:
Demand and savings deposits, non-maturity	1,598,967	1,573,709
Time deposits	261,176	270,789
Total deposits	1,860,143	1,844,498
Short-term borrowings	38,005	37,256
Total liabilities	1,898,148	1,881,754
Off-Balance-Sheet:
Commitments to extend credit	$ 0	$ 0