Investment Securities (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013 Security	Jun. 30, 2012	Jun. 30, 2013 Security	Jun. 30, 2012	Dec. 31, 2012
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	$ 902,630		$ 902,630		$ 905,846
Gross Unrealized Gains	863		863		6,903
Gross Unrealized Losses	25,305		25,305		657
Total securities available for sale	878,188		878,188		912,092
Amortized Cost [Abstract]
Due in one year or less	10,598		10,598
Due in one year through five years	739,312		739,312
Due after five years through ten years	147,646		147,646
Due after ten years	5,064		5,064
Amortized Cost	902,620		902,620
Fair Value [Abstract]
Due in one year or less	10,730		10,730
Due in one year through five years	720,947		720,947
Due after five years through ten years	141,325		141,325
Due after ten years	5,176		5,176
Available for sale debt securities, fair value	878,178		878,178
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	794,343		794,343		204,463
12 months or more - Fair Value	401		401		0
Total - Fair Value	794,744		794,744		204,463
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	25,304		25,304		657
12 months or more - Gross Unrealized Loss	1		1		0
Total - Gross Unrealized Loss	25,305		25,305		657
Proceeds from sales and calls of securities available for sale, gross realized gains and gross realized losses [Abstract]
Proceeds from sales	118,560	16,141	118,560	53,998
Proceeds from calls	96,417	313,024	205,414	547,749
Gross realized gains	1,512	157	1,514	932
Gross realized losses	80	102	80	200
Income tax expense recognized on net gains on sales and calls of securities available for sale	573	22	574	293
Amortized cost and fair value of the held to maturity securities [Abstract]
Amortized Cost	98,789		98,789		143,426
Gross Unrecognized Gains	4,666		4,666		7,700
Gross Unrecognized Losses	124		124		0
Fair Value	103,331		103,331		151,126
Amortized Cost [Abstract]
Due in one year or less	0		0
Due in one year through five years	98,789		98,789
Due in five years through ten years	0		0
Amortized Cost	98,789		98,789
Fair Value [Abstract]
Due in one year or less	0		0
Due in one year through five years	103,331		103,331
Due in five years through ten years	0		0
Fair Value	103,331		103,331
Investment security impairment - Other Than Temporary Impairment [Abstract]
Number of securities in portfolio	222		222
Number of securities in portfolio in unrealized loss position	102		102
Mortgage-backed securities and collateralized mortgage obligations-residential [Member]
Amortized cost and fair value of the held to maturity securities [Abstract]
Amortized Cost	88,852		88,852		108,471
Gross Unrecognized Gains	3,426		3,426		5,724
Gross Unrecognized Losses	124		124		0
Fair Value	92,154		92,154		114,195
Corporate bonds [Member]
Amortized cost and fair value of the held to maturity securities [Abstract]
Amortized Cost	9,937		9,937		34,955
Gross Unrecognized Gains	1,240		1,240		1,976
Gross Unrecognized Losses	0		0		0
Fair Value	11,177		11,177		36,931
U. S. government sponsored enterprises [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	191,032		191,032		262,063
Gross Unrealized Gains	78		78		1,055
Gross Unrealized Losses	2,977		2,977		10
Total securities available for sale	188,133		188,133		263,108
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	166,770		166,770		15,491
12 months or more - Fair Value	0		0		0
Total - Fair Value	166,770		166,770		15,491
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	2,977		2,977		10
12 months or more - Gross Unrealized Loss	0		0		0
Total - Gross Unrealized Loss	2,977		2,977		10
State and political subdivisions [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	11,851		11,851		25,815
Gross Unrealized Gains	308		308		642
Gross Unrealized Losses	0		0		0
Total securities available for sale	12,159		12,159		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	520,391		520,391		515,322
Gross Unrealized Gains	340		340		3,982
Gross Unrealized Losses	15,938		15,938		528
Total securities available for sale	504,793		504,793		518,776
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	475,756		475,756		178,689
12 months or more - Fair Value	0		0		0
Total - Fair Value	475,756		475,756		178,689
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	15,938		15,938		528
12 months or more - Gross Unrealized Loss	0		0		0
Total - Gross Unrealized Loss	15,938		15,938		528
Corporate bonds [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	53,352		53,352		26,312
Gross Unrealized Gains	137		137		336
Gross Unrealized Losses	436		436		119
Total securities available for sale	53,053		53,053		26,529
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	32,427		32,427		10,283
12 months or more - Fair Value	401		401		0
Total - Fair Value	32,828		32,828		10,283
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	435		435		119
12 months or more - Gross Unrealized Loss	1		1		0
Total - Gross Unrealized Loss	436		436		119
Small Business Administration-guaranteed participation securities [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	114,247		114,247		75,674
Gross Unrealized Gains	0		0		888
Gross Unrealized Losses	5,582		5,582		0
Total securities available for sale	108,665		108,665		76,562
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	108,665		108,665
12 months or more - Fair Value	0		0
Total - Fair Value	108,665		108,665
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	5,582		5,582
12 months or more - Gross Unrealized Loss	0		0
Total - Gross Unrealized Loss	5,582		5,582
Mortgage-backed securities and collateralized mortgage obligations-Commercial [Member]
Amortized cost and fair value of the securities available for sale [Abstract]
Amortized Cost	11,097		11,097
Gross Unrealized Gains	0		0
Gross Unrealized Losses	372		372
Total securities available for sale	10,725		10,725
Available for sale securities unrealized loss position - Fair Value [Abstract]
Less than 12 months - Fair Value	10,725		10,725
12 months or more - Fair Value	0		0
Total - Fair Value	10,725		10,725
Available for sale securities unrealized loss position - Gross Unrealized Loss [Abstract]
Less than 12 months - Gross Unrealized Loss	372		372
12 months or more - Gross Unrealized Loss	0		0
Total - Gross Unrealized Loss	372		372
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	902,620		902,620		905,836
Gross Unrealized Gains	863		863		6,903
Gross Unrealized Losses	25,305		25,305		657
Total securities available for sale	878,178		878,178		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