Investment Securities (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Trading securities	$ 0		$ 0		$ 0
Held-to-maturity securities	0		0		0
Available-for-sale Securities, Balance Sheet, Reported Amounts [Abstract]
Amortized cost	404,623		404,623		365,755
Unrealized gains	3,643		3,643		8,236
Unrealized losses	(7,990)		(7,990)		(1,023)
Fair value	400,276		400,276		372,968
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	222,222		222,222		59,705
12 months or more, fair value	28,654		28,654		12,428
Total fair value	250,876		250,876		72,133
Less than 12 months, unrealized losses	(6,402)		(6,402)		(433)
12 months or more, unrealized losses	(1,588)		(1,588)		(590)
Unrealized losses	(7,990)		(7,990)		(1,023)
Number of securities temporarily impaired	80		80			25
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Three months or less, amortized cost	1,411		1,411
Over three months to one year, amortized cost	2,519		2,519
After one year through three years, amortized cost	44,646		44,646
After year three through five years, amortized cost	233,541		233,541
After five through ten years, amortized cost	83,607		83,607
After ten years, amortized cost	38,899		38,899
Total amortized cost	404,623		404,623
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Three months or less, fair value	1,415		1,415
Over three months to one year, fair value	2,550		2,550
After one year through three years, fair value	45,390		45,390
After three years through five years, fair value	230,633		230,633
After five years through ten years, fair value	82,337		82,337
After ten years, fair value	37,951		37,951
Total cost - fair value	400,276		400,276
Pledged Financial Instruments, Not Separately Reported, Securities [Abstract]
To state and local governments to secure public deposits, amortized cost	53,742		53,742
To Federal Reserve Bank to secure borrowings, amortized cost	18,226		18,226
To Federal Home Loan Bank to secure borrowings, amortized cost	525		525
Other securities pledged, principally to secure deposits, amortized cost	12,584		12,584
Total pledged investment securities, amortized cost	85,077		85,077
Pledged Assets Separately Reported, Securities Pledged as Collateral, at Fair Value, by Type of Agreement [Abstract]
To state and local governments to secure public deposits, fair value	55,297		55,297
To Federal Reserve Bank to secure borrowings, fair value	18,259		18,259
To Federal Home Loan Bank to secure borrowings, fair value	544		544
Other securities pledged, principally to secure deposits, fair value	13,035		13,035
Total pledged investment securities, fair value	87,135		87,135
Gain on sale of investment securities [Abstract]
Gross realized gains	0	345	556	689
Gross realized losses	0	0	0	(2)
Gain on sale of investment securities, net	0	345	556	687
U.S. government agencies [Member]
Available-for-sale Securities, Balance Sheet, Reported Amounts [Abstract]
Amortized cost	85,789		85,789		87,297
Unrealized gains	759		759		1,321
Unrealized losses	(633)		(633)		(32)
Fair value	85,915		85,915		88,586
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	40,631		40,631		12,056
12 months or more, fair value	0		0		0
Total fair value	40,631		40,631		12,056
Less than 12 months, unrealized losses	(633)		(633)		(32)
12 months or more, unrealized losses	0		0		0
Unrealized losses	(633)		(633)		(32)
Residential pass-through securities [Member]
Available-for-sale Securities, Balance Sheet, Reported Amounts [Abstract]
Amortized cost	171,312		171,312		165,175
Unrealized gains	911		911		3,430
Unrealized losses	(3,404)		(3,404)		(182)
Fair value	168,819		168,819		168,423
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	89,801		89,801		27,680
12 months or more, fair value	23,936		23,936		0
Total fair value	113,737		113,737		27,680
Less than 12 months, unrealized losses	(2,116)		(2,116)		(182)
12 months or more, unrealized losses	(1,288)		(1,288)		0
Unrealized losses	(3,404)		(3,404)		(182)
Taxable state and political subdivisions [Member]
Available-for-sale Securities, Balance Sheet, Reported Amounts [Abstract]
Amortized cost	2,295		2,295		4,759
Unrealized gains	215		215		553
Unrealized losses	0		0		0
Fair value	2,510		2,510		5,312
Tax exempt state and political subdivisions [Member]
Available-for-sale Securities, Balance Sheet, Reported Amounts [Abstract]
Amortized cost	71,678		71,678		56,431
Unrealized gains	1,711		1,711		2,703
Unrealized losses	(990)		(990)		(149)
Fair value	72,399		72,399		58,985
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	36,019		36,019		10,113
12 months or more, fair value	0		0		0
Total fair value	36,019		36,019		10,113
Less than 12 months, unrealized losses	(990)		(990)		(149)
12 months or more, unrealized losses	0		0		0
Unrealized losses	(990)		(990)		(149)
Corporate obligations [Member]
Available-for-sale Securities, Balance Sheet, Reported Amounts [Abstract]
Amortized cost	11,000		11,000		11,000
Unrealized gains	0		0		0
Unrealized losses	(252)		(252)		(565)
Fair value	10,748		10,748		10,435
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	7,943		7,943		0
12 months or more, fair value	2,805		2,805		10,435
Total fair value	10,748		10,748		10,435
Less than 12 months, unrealized losses	(57)		(57)		0
12 months or more, unrealized losses	(195)		(195)		(565)
Unrealized losses	(252)		(252)		(565)
Agency-issued collateralized mortgage obligations [Member]
Available-for-sale Securities, Balance Sheet, Reported Amounts [Abstract]
Amortized cost	36,653		36,653		13,967
Unrealized gains	47		47		79
Unrealized losses	(962)		(962)		0
Fair value	35,738		35,738		14,046
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	25,594		25,594
12 months or more, fair value	0		0
Total fair value	25,594		25,594
Less than 12 months, unrealized losses	(962)		(962)
12 months or more, unrealized losses	0		0
Unrealized losses	(962)		(962)
Asset-backed securities [Member]
Available-for-sale Securities, Balance Sheet, Reported Amounts [Abstract]
Amortized cost	23,878		23,878		25,108
Unrealized gains	0		0		150
Unrealized losses	(1,644)		(1,644)		(70)
Fair value	22,234		22,234		25,188
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	22,234		22,234		9,856
12 months or more, fair value	0		0		0
Total fair value	22,234		22,234		9,856
Less than 12 months, unrealized losses	(1,644)		(1,644)		(70)
12 months or more, unrealized losses	0		0		0
Unrealized losses	(1,644)		(1,644)		(70)
Investments in mutual funds and other equities [Member]
Available-for-sale Securities, Balance Sheet, Reported Amounts [Abstract]
Amortized cost	2,018		2,018		2,018
Unrealized gains	0		0		0
Unrealized losses	(105)		(105)		(25)
Fair value	1,913		1,913		1,993
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	0		0		0
12 months or more, fair value	1,913		1,913		1,993
Total fair value	1,913		1,913		1,993
Less than 12 months, unrealized losses	0		0		0
12 months or more, unrealized losses	(105)		(105)		(25)
Unrealized losses	$ (105)		$ (105)		$ (25)