Investment Securities (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013 Security	Sep. 30, 2012	Sep. 30, 2013 Security	Sep. 30, 2012	Dec. 31, 2012
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	$ 931,427		$ 931,427		$ 905,846
Gross Unrealized Gains	1,450		1,450		6,903
Gross Unrealized Losses	24,431		24,431		657
Total securities available for sale	908,446		908,446		912,092
Amortized Cost [Abstract]
Due in one year or less	11,066		11,066
Due in one year through five years	613,821		613,821
Due after five years through ten years	302,411		302,411
Due after ten years	4,119		4,119
Amortized Cost	931,417		931,417
Fair Value [Abstract]
Due in one year or less	11,160		11,160
Due in one year through five years	605,382		605,382
Due after five years through ten years	287,710		287,710
Due after ten years	4,184		4,184
Available for sale debt securities, fair value	908,436		908,436
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	787,740		787,740		204,463
12 months or more - Fair Value	400		400		0
Total - Fair Value	788,140		788,140		204,463
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	24,429		24,429		657
12 months or more - Gross Unrealized Loss	2		2		0
Total - Gross Unrealized Loss	24,431		24,431		657
Held-to-maturity securities, unrecognized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	5,146		5,146
12 months or more - Fair Value	0		0
Total - Fair Value	5,146		5,146
Held-to-maturity securities, unrecognized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	51		51
12 months or more - Gross Unrealized Loss	0		0
Total - Gross Unrealized Loss	51		51
Proceeds from sales and calls of securities available for sale, gross realized gains and gross realized losses [Abstract]
Proceeds from sales	0	26,299	118,560	80,297
Proceeds from calls	31,704	278,165	237,118	825,914
Gross realized gains	0	666	1,514	1,598
Gross realized losses	0	0	80	200
Income tax expense recognized on net gains on sales and calls of securities available for sale	0	266	574	559
Amortized cost and fair value of the held to maturity securities [Abstract]
Amortized Cost	91,278		91,278		143,426
Gross Unrecognized Gains	4,741		4,741		7,700
Gross Unrecognized Losses	51		51		0
Fair Value	95,968		95,968		151,126
Amortized Cost [Abstract]
Due in one year or less	0		0
Due in one year through five years	91,278		91,278
Due in five years through ten years	0		0
Amortized Cost	91,278		91,278
Fair Value [Abstract]
Due in one year or less	0		0
Due in one year through five years	95,968		95,968
Due in five years through ten years	0		0
Fair Value	95,968		95,968
Investment security impairment - Other Than Temporary Impairment [Abstract]
Number of securities in portfolio	225		225
Number of securities in portfolio in unrealized loss position	96		96
Mortgage-backed securities and collateralized mortgage obligations-residential [Member]
Amortized cost and fair value of the held to maturity securities [Abstract]
Amortized Cost	81,337		81,337		108,471
Gross Unrecognized Gains	3,336		3,336		5,724
Gross Unrecognized Losses	51		51		0
Fair Value	84,622		84,622		114,195
Corporate bonds [Member]
Amortized cost and fair value of the held to maturity securities [Abstract]
Amortized Cost	9,941		9,941		34,955
Gross Unrecognized Gains	1,405		1,405		1,976
Gross Unrecognized Losses	0		0		0
Fair Value	11,346		11,346		36,931
U. S. government sponsored enterprises [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	196,033		196,033		262,063
Gross Unrealized Gains	62		62		1,055
Gross Unrealized Losses	2,481		2,481		10
Total securities available for sale	193,614		193,614		263,108
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	177,267		177,267		15,491
12 months or more - Fair Value	0		0		0
Total - Fair Value	177,267		177,267		15,491
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	2,481		2,481		10
12 months or more - Gross Unrealized Loss	0		0		0
Total - Gross Unrealized Loss	2,481		2,481		10
State and political subdivisions [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	10,978		10,978		25,815
Gross Unrealized Gains	221		221		642
Gross Unrealized Losses	0		0		0
Total securities available for sale	11,199		11,199		26,457
Mortgage-backed securities and collateralized mortgage obligations-residential [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	546,879		546,879		515,322
Gross Unrealized Gains	1,056		1,056		3,982
Gross Unrealized Losses	13,634		13,634		528
Total securities available for sale	534,301		534,301		518,776
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	463,190		463,190		178,689
12 months or more - Fair Value	0		0		0
Total - Fair Value	463,190		463,190		178,689
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	13,634		13,634		528
12 months or more - Gross Unrealized Loss	0		0		0
Total - Gross Unrealized Loss	13,634		13,634		528
Held-to-maturity securities, unrecognized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	5,146		5,146
12 months or more - Fair Value	0		0
Total - Fair Value	5,146		5,146
Held-to-maturity securities, unrecognized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	51		51
12 months or more - Gross Unrealized Loss	0		0
Total - Gross Unrealized Loss	51		51
Corporate bonds [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	53,127		53,127		26,312
Gross Unrealized Gains	111		111		336
Gross Unrealized Losses	144		144		119
Total securities available for sale	53,094		53,094		26,529
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	31,705		31,705		10,283
12 months or more - Fair Value	400		400		0
Total - Fair Value	32,105		32,105		10,283
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	142		142		119
12 months or more - Gross Unrealized Loss	2		2		0
Total - Gross Unrealized Loss	144		144		119
Small Business Administration-guaranteed participation securities [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	112,719		112,719		75,674
Gross Unrealized Gains	0		0		888
Gross Unrealized Losses	7,856		7,856		0
Total securities available for sale	104,863		104,863		76,562
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	104,863		104,863
12 months or more - Fair Value	0		0
Total - Fair Value	104,863		104,863
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	7,856		7,856
12 months or more - Gross Unrealized Loss	0		0
Total - Gross Unrealized Loss	7,856		7,856
Mortgage-backed securities and collateralized mortgage obligations-Commercial [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	11,031		11,031
Gross Unrealized Gains	0		0
Gross Unrealized Losses	316		316
Total securities available for sale	10,715		10,715
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	10,715		10,715
12 months or more - Fair Value	0		0
Total - Fair Value	10,715		10,715
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	316		316
12 months or more - Gross Unrealized Loss	0		0
Total - Gross Unrealized Loss	316		316
Other [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	650		650		650
Gross Unrealized Gains	0		0		0
Gross Unrealized Losses	0		0		0
Total securities available for sale	650		650		650
Debt securities [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	931,417		931,417		905,836
Gross Unrealized Gains	1,450		1,450		6,903
Gross Unrealized Losses	24,431		24,431		657
Total securities available for sale	908,436		908,436		912,082
Equity securities [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	10		10		10
Gross Unrealized Gains	0		0		0
Gross Unrealized Losses	0		0		0
Total securities available for sale	$ 10		$ 10		$ 10