Investment Securities (Summary of Investment Securities with Gross Unrealized Losses) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	$ 175,300	$ 554,907	$ 293,885
Less Than 12 Months, Gross Unrealized Losses	1,238	5,945	2,114
12 Months or More, Fair Value	221,011	133,159	135,889
12 Months or More, Gross Unrealized Losses	2,268	3,140	6,954
Total, Fair Value	396,311	688,066	429,774
Total, Gross Unrealized Losses	3,506	9,085	9,068
Government sponsored agencies [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	2,501	114,640	27,889
Less Than 12 Months, Gross Unrealized Losses	1	292	64
12 Months or More, Fair Value	20,275	21,681	18,896
12 Months or More, Gross Unrealized Losses	490	508	37
Total, Fair Value	22,776	136,321	46,785
Total, Gross Unrealized Losses	491	800	101
State and political subdivisions [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	83,997	195,285	156,010
Less Than 12 Months, Gross Unrealized Losses	1,067	2,891	1,989
12 Months or More, Fair Value	96,143	68,361	49,839
12 Months or More, Gross Unrealized Losses	920	1,627	2,940
Total, Fair Value	180,140	263,646	205,849
Total, Gross Unrealized Losses	1,987	4,518	4,929
Residential mortgage-backed securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	54,163	169,226	82,303
Less Than 12 Months, Gross Unrealized Losses	63	2,146	28
12 Months or More, Fair Value	63,869	3,435	3,847
12 Months or More, Gross Unrealized Losses	185	76	28
Total, Fair Value	118,032	172,661	86,150
Total, Gross Unrealized Losses	248	2,222	56
Collateralized Mortgage Obligations [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	29,973	60,459	22,694
Less Than 12 Months, Gross Unrealized Losses	34	408	22
12 Months or More, Fair Value	35,489	39,382	41,061
12 Months or More, Gross Unrealized Losses	407	729	696
Total, Fair Value	65,462	99,841	63,755
Total, Gross Unrealized Losses	441	1,137	718
Corporate bonds [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	4,666	9,532	4,989
Less Than 12 Months, Gross Unrealized Losses	73	200	11
12 Months or More, Fair Value	4,950	0	14,946
12 Months or More, Gross Unrealized Losses	51	0	53
Total, Fair Value	9,616	9,532	19,935
Total, Gross Unrealized Losses	124	200	64
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	285	300	7,300
12 Months or More, Gross Unrealized Losses	215	200	3,200
Total, Fair Value	285	300	7,300
Total, Gross Unrealized Losses	$ 215	200	$ 3,200
US Treasury Securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value		5,765
Less Than 12 Months, Gross Unrealized Losses		8
12 Months or More, Fair Value		0
12 Months or More, Gross Unrealized Losses		0
Total, Fair Value		5,765
Total, Gross Unrealized Losses		$ 8