Investment Securities (Summary of Investment Securities with Gross Unrealized Losses) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	$ 559,269	$ 141,129	$ 173,205
Less Than 12 Months, Gross Unrealized Losses	10,393	2,734	2,206
12 Months or More, Fair Value	53,844	86,618	109,603
12 Months or More, Gross Unrealized Losses	4,892	6,351	6,569
Total, Fair Value	613,113	227,747	282,808
Total, Gross Unrealized Losses	15,285	9,085	8,775
Government sponsored agencies [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	58,646	46,103	30,177
Less Than 12 Months, Gross Unrealized Losses	400	213	61
12 Months or More, Fair Value	0	0	9,516
12 Months or More, Gross Unrealized Losses	0	0	20
Total, Fair Value	58,646	46,103	39,693
Total, Gross Unrealized Losses	400	213	81
State and political subdivisions [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	128,062	70,675	49,355
Less Than 12 Months, Gross Unrealized Losses	4,707	2,257	1,100
12 Months or More, Fair Value	19,378	8,046	8,258
12 Months or More, Gross Unrealized Losses	482	1,110	73
Total, Fair Value	147,440	78,721	57,613
Total, Gross Unrealized Losses	5,189	3,367	1,173
Residential mortgage-backed securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	267,211	273	13,038
Less Than 12 Months, Gross Unrealized Losses	4,217	1	23
12 Months or More, Fair Value	257	1,305	19,988
12 Months or More, Gross Unrealized Losses	2	8	177
Total, Fair Value	267,468	1,578	33,026
Total, Gross Unrealized Losses	4,219	9	200
Collateralized Mortgage Obligations [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	100,469	19,331	30,651
Less Than 12 Months, Gross Unrealized Losses	939	10	296
12 Months or More, Fair Value	8,083	36,835	52,335
12 Months or More, Gross Unrealized Losses	34	172	306
Total, Fair Value	108,552	56,166	82,986
Total, Gross Unrealized Losses	973	182	602
Corporate bonds [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	4,881	4,747	49,984
Less Than 12 Months, Gross Unrealized Losses	130	253	726
12 Months or More, Fair Value	19,876	34,707	14,831
12 Months or More, Gross Unrealized Losses	124	286	168
Total, Fair Value	24,757	39,454	64,815
Total, Gross Unrealized Losses	254	539	894
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	4,675
12 Months or More, Gross Unrealized Losses	4,250	4,775	5,825
Total, Fair Value	6,250	5,725	4,675
Total, Gross Unrealized Losses	$ 4,250	$ 4,775	$ 5,825