Investment Securities (Summary of Investment Securities with Gross Unrealized Losses) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	$ 554,907	$ 317,885
Less Than 12 Months, Gross Unrealized Losses	5,945	3,998
12 Months or More, Fair Value	133,159	302,630
12 Months or More, Gross Unrealized Losses	3,140	7,295
Total, Fair Value	688,066	620,515
Total, Gross Unrealized Losses	9,085	11,293
US Treasury Securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	5,765	8,259
Less Than 12 Months, Gross Unrealized Losses	8	13
12 Months or More, Fair Value	0	0
12 Months or More, Gross Unrealized Losses	0	0
Total, Fair Value	5,765	8,259
Total, Gross Unrealized Losses	8	13
Government sponsored agencies [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	114,640	166,963
Less Than 12 Months, Gross Unrealized Losses	292	406
12 Months or More, Fair Value	21,681	31,927
12 Months or More, Gross Unrealized Losses	508	105
Total, Fair Value	136,321	198,890
Total, Gross Unrealized Losses	800	511
State and political subdivisions [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	195,285	62,310
Less Than 12 Months, Gross Unrealized Losses	2,891	3,348
12 Months or More, Fair Value	68,361	36,847
12 Months or More, Gross Unrealized Losses	1,627	1,226
Total, Fair Value	263,646	99,157
Total, Gross Unrealized Losses	4,518	4,574
Residential mortgage-backed securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	169,226	17,276
Less Than 12 Months, Gross Unrealized Losses	2,146	52
12 Months or More, Fair Value	3,435	180,194
12 Months or More, Gross Unrealized Losses	76	1,491
Total, Fair Value	172,661	197,470
Total, Gross Unrealized Losses	2,222	1,543
Collateralized mortgage obligations [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	60,459	63,077
Less Than 12 Months, Gross Unrealized Losses	408	179
12 Months or More, Fair Value	39,382	31,620
12 Months or More, Gross Unrealized Losses	729	1,015
Total, Fair Value	99,841	94,697
Total, Gross Unrealized Losses	1,137	1,194
Corporate bonds [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	9,532	0
Less Than 12 Months, Gross Unrealized Losses	200	0
12 Months or More, Fair Value	0	14,952
12 Months or More, Gross Unrealized Losses	0	48
Total, Fair Value	9,532	14,952
Total, Gross Unrealized Losses	200	48
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	300	7,090
12 Months or More, Gross Unrealized Losses	200	3,410
Total, Fair Value	300	7,090
Total, Gross Unrealized Losses	$ 200	$ 3,410