Investment Securities - Amortized Cost and Estimated Fair Value of Held to Maturity Securities and Available for Sale Securities by Contractual Maturity (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Securities Available-for-Sale:
Total Amortized Cost	$ 427,868	$ 416,898
Total Gross Unrealized Gains	11,531	13,097
Total Gross Unrealized Losses	(284)	(261)
Total Fair Value	439,115	429,734	[1]
U.S. treasuries [Member]
Securities Available-for-Sale:
Available-for-Sale Securities, Amortized Cost After 5 years to 10 years	4,962	4,960
Available-for-Sale Securities, Gross Unrealized Gains After 5 years to 10 years
Available-for-Sale Securities, Gross Unrealized Losses After 5 years to 10 years	(26)	(22)
Available-for-Sale Securities, Fair Value After 5 years to 10 years	4,936	4,938
Total Amortized Cost	4,962	4,960
Total Gross Unrealized Gains
Total Gross Unrealized Losses	(26)	(22)
Available-for-Sale Securities, Debt Total Fair Value	4,936	4,938
U.S. government corporations and agencies [Member]
Securities Available-for-Sale:
Available-for-Sale Securities, Amortized Cost Within 1 year	6,507	1,517
Available-for-Sale Securities, Gross Unrealized Gains Within 1 year	47	9
Available-for-Sale Securities, Gross Unrealized Losses Within 1 year
Available-for-Sale Securities, Fair Value Within 1 year	6,554	1,526
Available-for-Sale Securities, Amortized Cost After 1 year to 5 years	142,969	148,120
Available-for-Sale Securities, Gross Unrealized Gains After 1 year to 5 years	1,139	1,509
Available-for-Sale Securities, Gross Unrealized Losses After 1 year to 5 years	(45)	(70)
Available-for-Sale Securities, Fair Value After 1 year to 5 years	144,063	149,559
Available-for-Sale Securities, Amortized Cost After 5 years to 10 years	20,914	20,953
Available-for-Sale Securities, Gross Unrealized Gains After 5 years to 10 years	76	109
Available-for-Sale Securities, Gross Unrealized Losses After 5 years to 10 years	(12)	(5)
Available-for-Sale Securities, Fair Value After 5 years to 10 years	20,978	21,057
Total Amortized Cost	170,390	170,590
Total Gross Unrealized Gains	1,262	1,627
Total Gross Unrealized Losses	(57)	(75)
Available-for-Sale Securities, Debt Total Fair Value	171,595	172,142
State and political subdivisions [Member]
Securities Available-for-Sale:
Available-for-Sale Securities, Amortized Cost Within 1 year	4,603	4,607
Available-for-Sale Securities, Gross Unrealized Gains Within 1 year	45	75
Available-for-Sale Securities, Gross Unrealized Losses Within 1 year
Available-for-Sale Securities, Fair Value Within 1 year	4,648	4,682
Available-for-Sale Securities, Amortized Cost After 1 year to 5 years	4,479	4,130
Available-for-Sale Securities, Gross Unrealized Gains After 1 year to 5 years	79	88
Available-for-Sale Securities, Gross Unrealized Losses After 1 year to 5 years		(19)
Available-for-Sale Securities, Fair Value After 1 year to 5 years	4,558	4,199
Available-for-Sale Securities, Amortized Cost After 5 years to 10 years	39,505	36,499
Available-for-Sale Securities, Gross Unrealized Gains After 5 years to 10 years	1,238	1,245
Available-for-Sale Securities, Gross Unrealized Losses After 5 years to 10 years	(23)	(7)
Available-for-Sale Securities, Fair Value After 5 years to 10 years	40,720	37,737
Available-for-Sale Securities, Amortized Cost Over 10 years	68,511	70,495
Available-for-Sale Securities, Gross Unrealized Gains Over 10 years	4,029	5,055
Available-for-Sale Securities, Gross Unrealized Losses Over 10 years	(15)
Available-for-Sale Securities, Fair Value Over 10 years	72,525	75,550
Total Amortized Cost	117,098	115,731
Total Gross Unrealized Gains	5,391	6,463
Total Gross Unrealized Losses	(38)	(26)
Available-for-Sale Securities, Debt Total Fair Value	122,451	122,168
Residential mortgage-backed securities [Member]
Securities Available-for-Sale:
Available-for-Sale Securities, Amortized Cost After 5 years to 10 years	23,622	20,140
Available-for-Sale Securities, Gross Unrealized Gains After 5 years to 10 years	794	777
Available-for-Sale Securities, Gross Unrealized Losses After 5 years to 10 years
Available-for-Sale Securities, Fair Value After 5 years to 10 years	24,416	20,917
Available-for-Sale Securities, Amortized Cost Over 10 years	60,991	66,962
Available-for-Sale Securities, Gross Unrealized Gains Over 10 years	2,642	2,861
Available-for-Sale Securities, Gross Unrealized Losses Over 10 years
Available-for-Sale Securities, Fair Value Over 10 years	63,633	69,823
Total Amortized Cost	84,613	87,102
Total Gross Unrealized Gains	3,436	3,638
Total Gross Unrealized Losses
Available-for-Sale Securities, Debt Total Fair Value	88,049	90,740
Collateralized mortgage obligations [Member]
Securities Available-for-Sale:
Available-for-Sale Securities, Amortized Cost After 1 year to 5 years	210	41
Available-for-Sale Securities, Gross Unrealized Gains After 1 year to 5 years	4
Available-for-Sale Securities, Gross Unrealized Losses After 1 year to 5 years
Available-for-Sale Securities, Fair Value After 1 year to 5 years	214	41
Available-for-Sale Securities, Amortized Cost After 5 years to 10 years	4	626
Available-for-Sale Securities, Gross Unrealized Gains After 5 years to 10 years		7
Available-for-Sale Securities, Gross Unrealized Losses After 5 years to 10 years
Available-for-Sale Securities, Fair Value After 5 years to 10 years	4	633
Available-for-Sale Securities, Amortized Cost Over 10 years	23,400	25,698
Available-for-Sale Securities, Gross Unrealized Gains Over 10 years	568	645
Available-for-Sale Securities, Gross Unrealized Losses Over 10 years	(11)	(5)
Available-for-Sale Securities, Fair Value Over 10 years	23,957	26,338
Total Amortized Cost	23,614	26,365
Total Gross Unrealized Gains	572	652
Total Gross Unrealized Losses	(11)	(5)
Available-for-Sale Securities, Debt Total Fair Value	24,175	27,012
Corporate bonds [Member]
Securities Available-for-Sale:
Available-for-Sale Securities, Amortized Cost After 1 year to 5 years	4,994	4,993
Available-for-Sale Securities, Gross Unrealized Gains After 1 year to 5 years	38	21
Available-for-Sale Securities, Gross Unrealized Losses After 1 year to 5 years
Available-for-Sale Securities, Fair Value After 1 year to 5 years	5,032	5,014
Available-for-Sale Securities, Amortized Cost After 5 years to 10 years	15,520
Available-for-Sale Securities, Gross Unrealized Gains After 5 years to 10 years
Available-for-Sale Securities, Gross Unrealized Losses After 5 years to 10 years	(152)
Available-for-Sale Securities, Fair Value After 5 years to 10 years	15,368
Total Amortized Cost	20,514	4,993
Total Gross Unrealized Gains	38	21
Total Gross Unrealized Losses	(152)
Available-for-Sale Securities, Debt Total Fair Value	20,400	5,014
Money market mutual funds [Member]
Securities Available-for-Sale:
Available-for-Sale Securities, Amortized Cost Within 1 year	4,444	4,878
Available-for-Sale Securities, Gross Unrealized Gains Within 1 year
Available-for-Sale Securities, Gross Unrealized Losses Within 1 year
Available-for-Sale Securities, Fair Value Within 1 year	4,444	4,878
Total Amortized Cost	4,444	4,878
Total Gross Unrealized Gains
Total Gross Unrealized Losses
Available-for-Sale Securities, Debt Total Fair Value	4,444	4,878
Equity securities [Member]
Securities Available-for-Sale:
Available-for-Sale Securities Equity, No stated maturity Amortized Cost	2,233	2,279
Available-for-Sale Securities Equity, No stated maturity Gross Unrealized Gains	832	696
Available For Sale Securities Equity No stated maturity Gross Unrealized Losses		(133)
Available-for-Sale Securities Equity, No stated maturity Fair Value	3,065	2,842
Available-for-Sale Securities Equity, Total Amortized Cost	2,233	2,279
Available-for-Sale Securities Equity, Total Gross Unrealized Gains	832	696
Available-for-Sale Securities Equity, Total Gross Unrealized Losses		(133)
Available-for-Sale Securities, Equity Total Fair Value	3,065	2,842
Corporate bonds [Member]
Securities Held-to-Maturity
Held-to-Maturity, Amortized Cost Within 1 year	3,019	3,026
Held-to-Maturity, Gross Unrealized Gains Within 1 year	8	7
Held-to-Maturity, Fair Value Within 1 year	3,027	3,033
Held-to-Maturity After 1 year to 5 years, Amortized Cost	66,617	66,819
Held-to-Maturity After 1 year to 5 years, Gross Unrealized Gains	1,488	1,526
Held-to-Maturity After 1 year to 5 years, Gross Unrealized Losses	(33)	(51)
Held-to-Maturity After 1 year to 5 years, Fair Value	68,072	68,294
Held-to-Maturity, Amortized Cost	69,636	69,845
Held-to-Maturity, Gross Unrealized Gains	1,496	1,533
Held-to-Maturity, Gross Unrealized Losses	(33)	(51)
Held-to-Maturity, Fair Value	$ 71,099	$ 71,327

[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.