Investment Securities (Summary of Investment Securities with Gross Unrealized Losses) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	$ 570,518	$ 141,129	$ 141,107
Less Than 12 Months, Gross Unrealized Losses	12,375	2,734	2,536
12 Months or More, Fair Value	86,785	86,618	107,211
12 Months or More, Gross Unrealized Losses	6,609	6,351	5,661
Total, Fair Value	657,303	227,747	248,318
Total, Gross Unrealized Losses	18,984	9,085	8,197
Government sponsored agencies [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	43,816	46,103	39,729
Less Than 12 Months, Gross Unrealized Losses	223	213	248
12 Months or More, Fair Value	14,395	0	8,808
12 Months or More, Gross Unrealized Losses	181	0	18
Total, Fair Value	58,211	46,103	48,537
Total, Gross Unrealized Losses	404	213	266
State and political subdivisions [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	120,232	70,675	69,841
Less Than 12 Months, Gross Unrealized Losses	6,918	2,257	1,711
12 Months or More, Fair Value	30,915	8,046	1,533
12 Months or More, Gross Unrealized Losses	1,528	1,110	8
Total, Fair Value	151,147	78,721	71,374
Total, Gross Unrealized Losses	8,446	3,367	1,719
Residential mortgage-backed securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	267,495	273	32
Less Than 12 Months, Gross Unrealized Losses	3,532	1	1
12 Months or More, Fair Value	40	1,305	19,704
12 Months or More, Gross Unrealized Losses	2	8	15
Total, Fair Value	267,535	1,578	19,736
Total, Gross Unrealized Losses	3,534	9	16
Collateralized Mortgage Obligations [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	129,049	19,331	12,036
Less Than 12 Months, Gross Unrealized Losses	1,617	10	45
12 Months or More, Fair Value	15,302	36,835	47,066
12 Months or More, Gross Unrealized Losses	531	172	229
Total, Fair Value	144,351	56,166	59,102
Total, Gross Unrealized Losses	2,148	182	274
Corporate bonds [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	9,926	4,747	19,469
Less Than 12 Months, Gross Unrealized Losses	85	253	531
12 Months or More, Fair Value	19,883	34,707	24,900
12 Months or More, Gross Unrealized Losses	117	286	91
Total, Fair Value	29,809	39,454	44,369
Total, Gross Unrealized Losses	202	539	622
Trust Preferred Securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	0	0	0
Less Than 12 Months, Gross Unrealized Losses	0	0	0
12 Months or More, Fair Value	6,250	5,725	5,200
12 Months or More, Gross Unrealized Losses	4,250	4,775	5,300
Total, Fair Value	6,250	5,725	5,200
Total, Gross Unrealized Losses	$ 4,250	$ 4,775	$ 5,300