Investment Securities (Summary of Investment Securities with Gross Unrealized Losses) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	$ 317,885	$ 548,723
Less Than 12 Months, Gross Unrealized Losses	3,998	13,007
12 Months or More, Fair Value	302,630	73,865
12 Months or More, Gross Unrealized Losses	7,295	5,491
Total, Fair Value	620,515	622,588
Total, Gross Unrealized Losses	11,293	18,498
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
Government sponsored agencies [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	166,963	47,352
Less Than 12 Months, Gross Unrealized Losses	406	205
12 Months or More, Fair Value	31,927	14,031
12 Months or More, Gross Unrealized Losses	105	177
Total, Fair Value	198,890	61,383
Total, Gross Unrealized Losses	511	382
State and political subdivisions [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	62,310	126,345
Less Than 12 Months, Gross Unrealized Losses	3,348	6,475
12 Months or More, Fair Value	36,847	19,074
12 Months or More, Gross Unrealized Losses	1,226	378
Total, Fair Value	99,157	145,419
Total, Gross Unrealized Losses	4,574	6,853
Residential mortgage-backed securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	17,276	274,076
Less Than 12 Months, Gross Unrealized Losses	52	5,097
12 Months or More, Fair Value	180,194	0
12 Months or More, Gross Unrealized Losses	1,491	0
Total, Fair Value	197,470	274,076
Total, Gross Unrealized Losses	1,543	5,097
Collateralized mortgage obligations [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	63,077	84,995
Less Than 12 Months, Gross Unrealized Losses	179	1,127
12 Months or More, Fair Value	31,620	14,684
12 Months or More, Gross Unrealized Losses	1,015	512
Total, Fair Value	94,697	99,679
Total, Gross Unrealized Losses	1,194	1,639
Corporate bonds [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	0	14,931
Less Than 12 Months, Gross Unrealized Losses	0	78
12 Months or More, Fair Value	14,952	19,826
12 Months or More, Gross Unrealized Losses	48	174
Total, Fair Value	14,952	34,757
Total, Gross Unrealized Losses	48	252
Trust preferred securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	0	0
Less Than 12 Months, Gross Unrealized Losses	0	0
12 Months or More, Fair Value	7,090	6,250
12 Months or More, Gross Unrealized Losses	3,410	4,250
Total, Fair Value	7,090	6,250
Total, Gross Unrealized Losses	3,410	4,250
Preferred stock [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	0	1,024
Less Than 12 Months, Gross Unrealized Losses	0	25
12 Months or More, Fair Value	0	0
12 Months or More, Gross Unrealized Losses	0	0
Total, Fair Value	0	1,024
Total, Gross Unrealized Losses	$ 0	$ 25