Fair Value Disclosures - Assets, liabilities and off-balance sheet items not measured at fair value (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Assets:
Held-to-maturity securities	$ 70,029	$ 71,327	[1]
Deposits:
Time deposits	299,016	331,511	[1]
Reported Value Measurement [Member]
Assets:
Cash and short-term interest-earning assets	86,554	146,112
Held-to-maturity securities	69,425	69,845
Loans held for sale		4,530
Net loans and leases held for investment	1,436,951	1,412,140
Mortgage servicing rights	5,227
Other real estate owned	1,650
Total assets	1,599,807	1,632,627
Deposits:
Demand and savings deposits, non-maturity	1,574,035	1,533,822
Time deposits	299,016	331,511
Total deposits	1,873,051	1,865,333
Short-term borrowings	45,388	96,282
Long-term borrowings	20,619	20,994
Total liabilities	1,939,058	1,982,609
Off-Balance-Sheet:
Commitments to extend credit
Estimate of Fair Value Measurement [Member]
Assets:
Cash and short-term interest-earning assets	86,554	146,112
Held-to-maturity securities	70,029	71,327
Loans held for sale		4,653
Net loans and leases held for investment	1,457,116	1,433,990
Mortgage servicing rights	6,476
Other real estate owned	1,650
Total assets	1,621,825	1,656,082
Deposits:
Demand and savings deposits, non-maturity	1,574,035	1,533,822
Time deposits	297,283	334,164
Total deposits	1,871,318	1,867,986
Short-term borrowings	43,474	94,066
Long-term borrowings	20,583	20,965
Total liabilities	1,935,375	1,983,017
Off-Balance-Sheet:
Commitments to extend credit	(1,318)	(1,286)
Estimate of Fair Value Measurement [Member] | Level 1 [Member]
Assets:
Cash and short-term interest-earning assets	86,554	146,112
Held-to-maturity securities
Loans held for sale
Net loans and leases held for investment
Mortgage servicing rights
Other real estate owned
Total assets	86,554	146,112
Deposits:
Demand and savings deposits, non-maturity	1,574,035	1,533,822
Time deposits
Total deposits	1,574,035	1,533,822
Short-term borrowings
Long-term borrowings
Total liabilities	1,574,035	1,533,822
Off-Balance-Sheet:
Commitments to extend credit
Estimate of Fair Value Measurement [Member] | Level 2 [Member]
Assets:
Cash and short-term interest-earning assets
Held-to-maturity securities	70,029	71,327
Loans held for sale		4,653
Net loans and leases held for investment
Mortgage servicing rights	6,476
Other real estate owned	1,650
Total assets	78,155	75,980
Deposits:
Demand and savings deposits, non-maturity
Time deposits	297,283	334,164
Total deposits	297,283	334,164
Short-term borrowings	43,474	94,066
Long-term borrowings	20,583	20,965
Total liabilities	361,340	449,195
Off-Balance-Sheet:
Commitments to extend credit	(1,318)	(1,286)
Estimate of Fair Value Measurement [Member] | Level 3 [Member]
Assets:
Cash and short-term interest-earning assets
Held-to-maturity securities
Loans held for sale
Net loans and leases held for investment	1,457,116	1,433,990
Mortgage servicing rights
Other real estate owned
Total assets	1,457,116	1,433,990
Deposits:
Demand and savings deposits, non-maturity
Time deposits
Total deposits
Short-term borrowings
Long-term borrowings
Total liabilities
Off-Balance-Sheet:
Commitments to extend credit

[1] Note: The consolidated balance sheet at December 31, 2012 has been derived from the audited financial statements at that date but does not include all of the information and footnotes required by U. S. generally accepted accounting principles for complete financial statements. See accompanying notes to the unaudited consolidated financial statements.