Fair Value Disclosures - Assets, Liabilities and Off-balance Sheet Items Not Measured at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Assets:
Held-to-maturity securities	$ 70,079	$ 71,327	[1]
Deposits:
Time deposits	289,782	331,511	[1]
Reported Value Measurement [Member]
Assets:
Cash and short-term interest-earning assets	79,458	146,112
Held-to-maturity securities	69,214	69,845
Loans held for sale	3,489	4,530
Net loans and leases held for investment	1,437,698	1,412,140
Mortgage servicing rights	5,484
Other real estate owned	1,650
Total assets	1,596,993	1,632,627
Deposits:
Demand and savings deposits, non-maturity	1,599,264	1,533,822
Time deposits	289,782	331,511
Total deposits	1,889,046	1,865,333
Short-term borrowings	46,733	96,282
Long-term borrowings		20,994
Total liabilities	1,935,779	1,982,609
Off-Balance-Sheet:
Commitments to extend credit
Estimate of Fair Value Measurement [Member]
Assets:
Cash and short-term interest-earning assets	79,458	146,112
Held-to-maturity securities	70,079	71,327
Loans held for sale	3,574	4,653
Net loans and leases held for investment	1,457,592	1,433,990
Mortgage servicing rights	7,029
Other real estate owned	1,650
Total assets	1,619,382	1,656,082
Deposits:
Demand and savings deposits, non-maturity	1,599,264	1,533,822
Time deposits	288,271	334,164
Total deposits	1,887,535	1,867,986
Short-term borrowings	44,841	94,066
Long-term borrowings		20,965
Total liabilities	1,932,376	1,983,017
Off-Balance-Sheet:
Commitments to extend credit	(1,342)	(1,286)
Estimate of Fair Value Measurement [Member] | Level 1 [Member]
Assets:
Cash and short-term interest-earning assets	79,458	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	79,458	146,112
Deposits:
Demand and savings deposits, non-maturity	1,599,264	1,533,822
Time deposits
Total deposits	1,599,264	1,533,822
Short-term borrowings
Long-term borrowings
Total liabilities	1,599,264	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	70,079	71,327
Loans held for sale	3,574	4,653
Net loans and leases held for investment
Mortgage servicing rights	7,029
Other real estate owned	1,650
Total assets	82,332	75,980
Deposits:
Demand and savings deposits, non-maturity
Time deposits	288,271	334,164
Total deposits	288,271	334,164
Short-term borrowings	44,841	94,066
Long-term borrowings		20,965
Total liabilities	333,112	449,195
Off-Balance-Sheet:
Commitments to extend credit	(1,342)	(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	1,457,592	1,433,990
Mortgage servicing rights
Other real estate owned
Total assets	1,457,592	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.