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	Dec. 31, 2012	Dec. 31, 2011
Securities Available-for-Sale:
Total Amortized Cost	$ 416,898	$ 414,119
Total Gross Unrealized Gains	13,097	12,423
Total Gross Unrealized Losses	(261)	(1,181)
Total Fair Value	429,734	425,361
U.S. treasuries [Member]
Securities Available-for-Sale:
Available-for-Sale Securities, Amortized Cost Within 1 year		2,525
Available-for-Sale Securities, Fair Value Within 1 year		2,525
Available-for-Sale Securities, Amortized Cost After 5 years to 10 years	4,960
Available-for-Sale Securities, Gross Unrealized Losses After 5 years to 10 years	(22)
Available-for-Sale Securities, Fair Value After 5 years to 10 years	4,938
Available-for-Sale Securities, Total Amortized Cost	4,960	2,525
Total Gross Unrealized Losses	(22)
Available-for-Sale Securities, Debt Total Fair Value	4,938	2,525
U.S. government corporations and agencies [Member]
Securities Available-for-Sale:
Available-for-Sale Securities, Amortized Cost Within 1 year	1,517	10,009
Available-for-Sale Securities, Gross Unrealized Gains Within 1 year	9	77
Available-for-Sale Securities, Fair Value Within 1 year	1,526	10,086
Available-for-Sale Securities, Amortized Cost After 1 year to 5 years	148,120	143,189
Available-for-Sale Securities, Gross Unrealized Gains After 1 year to 5 years	1,509	1,022
Available-for-Sale Securities, Gross Unrealized Losses After 1 year to 5 years	(70)	(33)
Available-for-Sale Securities, Fair Value After 1 year to 5 years	149,559	144,178
Available-for-Sale Securities, Amortized Cost After 5 years to 10 years	20,953
Available-for-Sale Securities, Gross Unrealized Gains After 5 years to 10 years	109
Available-for-Sale Securities, Gross Unrealized Losses After 5 years to 10 years	(5)
Available-for-Sale Securities, Fair Value After 5 years to 10 years	21,057
Available-for-Sale Securities, Total Amortized Cost	170,590	153,198
Total Gross Unrealized Gains	1,627	1,099
Total Gross Unrealized Losses	(75)	(33)
Available-for-Sale Securities, Debt Total Fair Value	172,142	154,264
State and political subdivisions [Member]
Securities Available-for-Sale:
Available-for-Sale Securities, Amortized Cost Within 1 year	4,607	752
Available-for-Sale Securities, Gross Unrealized Gains Within 1 year	75	5
Available-for-Sale Securities, Fair Value Within 1 year	4,682	757
Available-for-Sale Securities, Amortized Cost After 1 year to 5 years	4,130	10,082
Available-for-Sale Securities, Gross Unrealized Gains After 1 year to 5 years	88	308
Available-for-Sale Securities, Gross Unrealized Losses After 1 year to 5 years	(19)	(16)
Available-for-Sale Securities, Fair Value After 1 year to 5 years	4,199	10,374
Available-for-Sale Securities, Amortized Cost After 5 years to 10 years	36,499	11,846
Available-for-Sale Securities, Gross Unrealized Gains After 5 years to 10 years	1,245	664
Available-for-Sale Securities, Gross Unrealized Losses After 5 years to 10 years	(7)	(3)
Available-for-Sale Securities, Fair Value After 5 years to 10 years	37,737	12,507
Available-for-Sale Securities, Amortized Cost Over 10 years	70,495	87,896
Available-for-Sale Securities, Gross Unrealized Gains Over 10 years	5,055	5,472
Available-for-Sale Securities, Gross Unrealized Losses Over 10 years		(1)
Available-for-Sale Securities, Fair Value Over 10 years	75,550	93,367
Available-for-Sale Securities, Total Amortized Cost	115,731	110,576
Total Gross Unrealized Gains	6,463	6,449
Total Gross Unrealized Losses	(26)	(20)
Available-for-Sale Securities, Debt Total Fair Value	122,168	117,005
Residential mortgage-backed securities [Member]
Securities Available-for-Sale:
Available-for-Sale Securities, Amortized Cost After 5 years to 10 years	20,140	20,745
Available-for-Sale Securities, Gross Unrealized Gains After 5 years to 10 years	777	743
Available-for-Sale Securities, Fair Value After 5 years to 10 years	20,917	21,488
Available-for-Sale Securities, Amortized Cost Over 10 years	66,962	55,328
Available-for-Sale Securities, Gross Unrealized Gains Over 10 years	2,861	2,665
Available-for-Sale Securities, Gross Unrealized Losses Over 10 years		(680)
Available-for-Sale Securities, Fair Value Over 10 years	69,823	57,313
Available-for-Sale Securities, Total Amortized Cost	87,102	76,073
Total Gross Unrealized Gains	3,638	3,408
Total Gross Unrealized Losses		(680)
Available-for-Sale Securities, Debt Total Fair Value	90,740	78,801
Commercial mortgage obligations [Member]
Securities Available-for-Sale:
Available-for-Sale Securities, Amortized Cost After 1 year to 5 years	41
Available-for-Sale Securities, Fair Value After 1 year to 5 years	41
Available-for-Sale Securities, Amortized Cost After 5 years to 10 years	626	5,547
Available-for-Sale Securities, Gross Unrealized Gains After 5 years to 10 years	7	124
Available-for-Sale Securities, Fair Value After 5 years to 10 years	633	5,671
Available-for-Sale Securities, Amortized Cost Over 10 years	25,698	54,994
Available-for-Sale Securities, Gross Unrealized Gains Over 10 years	645	799
Available-for-Sale Securities, Gross Unrealized Losses Over 10 years	(5)
Available-for-Sale Securities, Fair Value Over 10 years	26,338	55,793
Available-for-Sale Securities, Total Amortized Cost	26,365	60,541
Total Gross Unrealized Gains	652	923
Total Gross Unrealized Losses	(5)
Available-for-Sale Securities, Debt Total Fair Value	27,012	61,464
Corporate bonds [Member]
Securities Available-for-Sale:
Available-for-Sale Securities, Amortized Cost After 1 year to 5 years	4,993	4,991
Available-for-Sale Securities, Gross Unrealized Gains After 1 year to 5 years	21
Available-for-Sale Securities, Gross Unrealized Losses After 1 year to 5 years		(224)
Available-for-Sale Securities, Fair Value After 1 year to 5 years	5,014	4,767
Available-for-Sale Securities, Total Amortized Cost	4,993	4,991
Total Gross Unrealized Gains	21
Total Gross Unrealized Losses		(224)
Available-for-Sale Securities, Debt Total Fair Value	5,014	4,767
Money market mutual funds [Member]
Securities Available-for-Sale:
Available-for-Sale Securities, Amortized Cost Within 1 year	4,878	3,851
Available-for-Sale Securities, Fair Value Within 1 year	4,878	3,851
Available-for-Sale Securities, Total Amortized Cost	4,878	3,851
Available-for-Sale Securities, Debt Total Fair Value	4,878	3,851
Equity securities [Member]
Securities Available-for-Sale:
Available-for-Sale Securities Equity, No stated maturity Amortized Cost	2,279	2,364
Available-for-Sale Securities Equity, No stated maturity Gross Unrealized Gains	696	544
Available For Sale Securities Equity No stated maturity Gross Unrealized Losses	(133)	(224)
Available-for-Sale Securities Equity, No stated maturity Fair Value	2,842	2,684
Available-for-Sale Securities Equity, Total Amortized Cost	2,279	2,364
Available-for-Sale Securities Equity, Total Gross Unrealized Gains	696	544
Available-for-Sale Securities Equity, Total Gross Unrealized Losses	(133)	(224)
Available-for-Sale Securities, Equity Total Fair Value	2,842	2,684
Corporate bonds [Member]
Securities Held-to-Maturity
Held-to-Maturity, Amortized Cost Within 1 year	3,026
Held-to-Maturity, Gross Unrealized Gains Within 1 year	7
Held-to-Maturity, Fair Value Within 1 year	3,033
Held-to-Maturity After 1 year to 5 years, Amortized Cost	66,819	45,804
Held-to-Maturity After 1 year to 5 years, Gross Unrealized Gains	1,526	154
Held-to-Maturity After 1 year to 5 years, Gross Unrealized Losses	(51)	(319)
Held-to-Maturity After 1 year to 5 years, Fair Value	68,294	45,639
Held-to-Maturity, Amortized Cost	69,845	45,804
Held-to-Maturity, Gross Unrealized Gains	1,533	154
Held-to-Maturity, Gross Unrealized Losses	(51)	(319)
Held-to-Maturity, Fair Value	$ 71,327	$ 45,639