Investment Securities (Summary of Investment Securities with Gross Unrealized Losses) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	$ 530,665	$ 317,885	$ 156,938
Less Than 12 Months, Gross Unrealized Losses	7,392	3,998	4,182
12 Months or More, Fair Value	146,094	302,630	370,668
12 Months or More, Gross Unrealized Losses	3,687	7,295	8,646
Total, Fair Value	676,759	620,515	527,606
Total, Gross Unrealized Losses	11,079	11,293	12,828
Government sponsored agencies [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	24,789	166,963	2,377
Less Than 12 Months, Gross Unrealized Losses	163	406	2
12 Months or More, Fair Value	14,715	31,927	44,786
12 Months or More, Gross Unrealized Losses	37	105	139
Total, Fair Value	39,504	198,890	47,163
Total, Gross Unrealized Losses	200	511	141
State and political subdivisions [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	258,503	62,310	92,279
Less Than 12 Months, Gross Unrealized Losses	5,433	3,348	4,047
12 Months or More, Fair Value	63,584	36,847	71,421
12 Months or More, Gross Unrealized Losses	2,493	1,226	2,282
Total, Fair Value	322,087	99,157	163,700
Total, Gross Unrealized Losses	7,926	4,574	6,329
Residential mortgage-backed securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	187,858	17,276	10,144
Less Than 12 Months, Gross Unrealized Losses	1,592	52	60
12 Months or More, Fair Value	3,643	180,194	197,042
12 Months or More, Gross Unrealized Losses	102	1,491	1,362
Total, Fair Value	191,501	197,470	207,186
Total, Gross Unrealized Losses	1,694	1,543	1,422
Collateralized Mortgage Obligations [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	49,845	63,077	47,142
Less Than 12 Months, Gross Unrealized Losses	155	179	68
12 Months or More, Fair Value	48,881	31,620	35,722
12 Months or More, Gross Unrealized Losses	826	1,015	1,060
Total, Fair Value	98,726	94,697	82,864
Total, Gross Unrealized Losses	981	1,194	1,128
Corporate bonds [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	9,670	0	4,996
Less Than 12 Months, Gross Unrealized Losses	49	0	5
12 Months or More, Fair Value	14,971	14,952	14,922
12 Months or More, Gross Unrealized Losses	29	48	78
Total, Fair Value	24,641	14,952	19,918
Total, Gross Unrealized Losses	78	48	83
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	300	7,090	6,775
12 Months or More, Gross Unrealized Losses	200	3,410	3,725
Total, Fair Value	300	7,090	6,775
Total, Gross Unrealized Losses	$ 200	3,410	$ 3,725
US Treasury Securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value		8,259
Less Than 12 Months, Gross Unrealized Losses		13
12 Months or More, Fair Value		0
12 Months or More, Gross Unrealized Losses		0
Total, Fair Value		8,259
Total, Gross Unrealized Losses		$ 13