Investment Securities (Summary of Investment Securities with Gross Unrealized Losses) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	$ 293,885	$ 317,885	$ 449,480
Less Than 12 Months, Gross Unrealized Losses	2,114	3,998	9,409
12 Months or More, Fair Value	135,889	302,630	105,584
12 Months or More, Gross Unrealized Losses	6,954	7,295	6,773
Total, Fair Value	429,774	620,515	555,064
Total, Gross Unrealized Losses	9,068	11,293	16,182
Government sponsored agencies [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	27,889	166,963	45,396
Less Than 12 Months, Gross Unrealized Losses	64	406	110
12 Months or More, Fair Value	18,896	31,927	15,204
12 Months or More, Gross Unrealized Losses	37	105	188
Total, Fair Value	46,785	198,890	60,600
Total, Gross Unrealized Losses	101	511	298
State and political subdivisions [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	156,010	62,310	79,787
Less Than 12 Months, Gross Unrealized Losses	1,989	3,348	4,942
12 Months or More, Fair Value	49,839	36,847	56,180
12 Months or More, Gross Unrealized Losses	2,940	1,226	2,041
Total, Fair Value	205,849	99,157	135,967
Total, Gross Unrealized Losses	4,929	4,574	6,983
Residential mortgage-backed securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	82,303	17,276	247,397
Less Than 12 Months, Gross Unrealized Losses	28	52	3,472
12 Months or More, Fair Value	3,847	180,194	0
12 Months or More, Gross Unrealized Losses	28	1,491	0
Total, Fair Value	86,150	197,470	247,397
Total, Gross Unrealized Losses	56	1,543	3,472
Collateralized Mortgage Obligations [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	22,694	63,077	76,900
Less Than 12 Months, Gross Unrealized Losses	22	179	885
12 Months or More, Fair Value	41,061	31,620	12,833
12 Months or More, Gross Unrealized Losses	696	1,015	411
Total, Fair Value	63,755	94,697	89,733
Total, Gross Unrealized Losses	718	1,194	1,296
Corporate bonds [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	4,989	0	0
Less Than 12 Months, Gross Unrealized Losses	11	0	0
12 Months or More, Fair Value	14,946	14,952	14,907
12 Months or More, Gross Unrealized Losses	53	48	93
Total, Fair Value	19,935	14,952	14,907
Total, Gross Unrealized Losses	64	48	93
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	7,300	7,090	6,460
12 Months or More, Gross Unrealized Losses	3,200	3,410	4,040
Total, Fair Value	7,300	7,090	6,460
Total, Gross Unrealized Losses	3,200	3,410	4,040
US Treasury Securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	0	8,259
Less Than 12 Months, Gross Unrealized Losses	0	13
12 Months or More, Fair Value	0	0
12 Months or More, Gross Unrealized Losses	0	0
Total, Fair Value	0	8,259
Total, Gross Unrealized Losses	$ 0	$ 13