Fair Value Disclosures - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Available-for-sale securities:
Investment securities available-for-sale	$ 445,202	$ 425,361	[1]
Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Investment securities available-for-sale	445,202	425,361
Total assets	448,622	426,440
Liabilities:
Total Liabilities	3,941	1,737
Fair Value, Measurements, Recurring [Member] | U.S. government treasuries [Member]
Available-for-sale securities:
Investment securities available-for-sale	4,952	2,525
Fair Value, Measurements, Recurring [Member] | U.S. government corporations and agencies [Member]
Available-for-sale securities:
Investment securities available-for-sale	180,523	154,264
Fair Value, Measurements, Recurring [Member] | State and political subdivisions [Member]
Available-for-sale securities:
Investment securities available-for-sale	124,196	117,005
Fair Value, Measurements, Recurring [Member] | Residential mortgage-backed securities [Member]
Available-for-sale securities:
Investment securities available-for-sale	98,793	78,801
Fair Value, Measurements, Recurring [Member] | Commercial mortgage obligations [Member]
Available-for-sale securities:
Investment securities available-for-sale	24,371	61,464
Fair Value, Measurements, Recurring [Member] | Corporate bonds [Member]
Available-for-sale securities:
Investment securities available-for-sale	5,006	4,767
Fair Value, Measurements, Recurring [Member] | Money market mutual funds [Member]
Available-for-sale securities:
Investment securities available-for-sale	4,500	3,851
Fair Value, Measurements, Recurring [Member] | Equity securities [Member]
Available-for-sale securities:
Investment securities available-for-sale	2,861	2,684
Fair Value, Measurements, Recurring [Member] | Interest rate locks with customers [Member]
Available-for-sale securities:
Derivative assets	3,420	1,079
Fair Value, Measurements, Recurring [Member] | Interest rate swap [Member]
Liabilities:
Liabilities	2,036	1,435
Fair Value, Measurements, Recurring [Member] | Forward loan commitments [Member]
Liabilities:
Liabilities	1,029	302
Fair Value, Measurements, Recurring [Member] | Contingent Consideration Liability [Member]
Liabilities:
Total Liabilities	876
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Available-for-sale securities:
Investment securities available-for-sale	12,313	9,060
Total assets	12,313	9,060
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | U.S. government treasuries [Member]
Available-for-sale securities:
Investment securities available-for-sale	4,952	2,525
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Money market mutual funds [Member]
Available-for-sale securities:
Investment securities available-for-sale	4,500	3,851
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Equity securities [Member]
Available-for-sale securities:
Investment securities available-for-sale	2,861	2,684
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Available-for-sale securities:
Investment securities available-for-sale	432,889	416,301
Total assets	436,309	417,380
Liabilities:
Total Liabilities	3,065	1,737
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S. government corporations and agencies [Member]
Available-for-sale securities:
Investment securities available-for-sale	180,523	154,264
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | State and political subdivisions [Member]
Available-for-sale securities:
Investment securities available-for-sale	124,196	117,005
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Residential mortgage-backed securities [Member]
Available-for-sale securities:
Investment securities available-for-sale	98,793	78,801
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Commercial mortgage obligations [Member]
Available-for-sale securities:
Investment securities available-for-sale	24,371	61,464
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Corporate bonds [Member]
Available-for-sale securities:
Investment securities available-for-sale	5,006	4,767
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Interest rate locks with customers [Member]
Available-for-sale securities:
Derivative assets	3,420	1,079
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Interest rate swap [Member]
Liabilities:
Liabilities	2,036	1,435
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Forward loan commitments [Member]
Liabilities:
Liabilities	1,029	302
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Liabilities:
Total Liabilities	876
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Contingent Consideration Liability [Member]
Liabilities:
Total Liabilities	$ 876

[1] Note: The consolidated balance sheet at December 31, 2011 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. Certain amounts have been reclassified to conform to the current-year presentation. See accompanying notes to the unaudited consolidated financial statements.