Fair Value Disclosures - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Available-for-sale securities:
Total available-for-sale securities	$ 439,115	$ 429,734	[1]
Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Total available-for-sale securities	439,115	429,734
Total assets	440,600	431,281
Liabilities:
Total Liabilities	2,899	2,866
Fair Value, Measurements, Recurring [Member] | U.S. treasuries [Member]
Available-for-sale securities:
Total available-for-sale securities	4,936	4,938
Fair Value, Measurements, Recurring [Member] | U.S. government corporations and agencies [Member]
Available-for-sale securities:
Total available-for-sale securities	171,595	172,142
Fair Value, Measurements, Recurring [Member] | State and political subdivisions [Member]
Available-for-sale securities:
Total available-for-sale securities	122,451	122,168
Fair Value, Measurements, Recurring [Member] | Residential mortgage-backed securities [Member]
Available-for-sale securities:
Total available-for-sale securities	88,049	90,740
Fair Value, Measurements, Recurring [Member] | Collateralized mortgage obligations [Member]
Available-for-sale securities:
Total available-for-sale securities	24,175	27,012
Fair Value, Measurements, Recurring [Member] | Corporate bonds [Member]
Available-for-sale securities:
Total available-for-sale securities	20,400	5,014
Fair Value, Measurements, Recurring [Member] | Money market mutual funds [Member]
Available-for-sale securities:
Total available-for-sale securities	4,444	4,878
Fair Value, Measurements, Recurring [Member] | Equity securities [Member]
Available-for-sale securities:
Total available-for-sale securities	3,065	2,842
Fair Value, Measurements, Recurring [Member] | Interest rate locks with customers [Member]
Available-for-sale securities:
Derivative assets	1,485	1,547
Fair Value, Measurements, Recurring [Member] | Interest rate swap [Member]
Liabilities:
Liabilities	1,747	1,909
Fair Value, Measurements, Recurring [Member] | Forward loan sale commitments [Member]
Liabilities:
Liabilities	222	54
Fair Value, Measurements, Recurring [Member] | Contingent consideration liability [Member]
Liabilities:
Total Liabilities	930	903
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Available-for-sale securities:
Total available-for-sale securities	12,445	12,658
Total assets	12,445	12,658
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | U.S. treasuries [Member]
Available-for-sale securities:
Total available-for-sale securities	4,936	4,938
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Money market mutual funds [Member]
Available-for-sale securities:
Total available-for-sale securities	4,444	4,878
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Equity securities [Member]
Available-for-sale securities:
Total available-for-sale securities	3,065	2,842
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Available-for-sale securities:
Total available-for-sale securities	426,670	417,076
Total assets	428,155	418,623
Liabilities:
Total Liabilities	1,969	1,963
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S. government corporations and agencies [Member]
Available-for-sale securities:
Total available-for-sale securities	171,595	172,142
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | State and political subdivisions [Member]
Available-for-sale securities:
Total available-for-sale securities	122,451	122,168
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Residential mortgage-backed securities [Member]
Available-for-sale securities:
Total available-for-sale securities	88,049	90,740
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Collateralized mortgage obligations [Member]
Available-for-sale securities:
Total available-for-sale securities	24,175	27,012
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Corporate bonds [Member]
Available-for-sale securities:
Total available-for-sale securities	20,400	5,014
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Interest rate locks with customers [Member]
Available-for-sale securities:
Derivative assets	1,485	1,547
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Interest rate swap [Member]
Liabilities:
Liabilities	1,747	1,909
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Forward loan sale commitments [Member]
Liabilities:
Liabilities	222	54
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Available-for-sale securities:
Total assets	0	0
Liabilities:
Total Liabilities	930	903
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Contingent consideration liability [Member]
Liabilities:
Total Liabilities	$ 930	$ 903

[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.