Investment Securities (Summary of Investment Securities with Gross Unrealized Losses) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	$ 1,478,240	$ 554,907
Less Than 12 Months, Gross Unrealized Losses	39,116	5,945
12 Months or More, Fair Value	56,897	133,159
12 Months or More, Gross Unrealized Losses	1,751	3,140
Total, Fair Value	1,535,137	688,066
Total, Gross Unrealized Losses	40,867	9,085
U.S. Treasury securities
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
Government sponsored agencies
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	105,702	114,640
Less Than 12 Months, Gross Unrealized Losses	1,707	292
12 Months or More, Fair Value	15,023	21,681
12 Months or More, Gross Unrealized Losses	361	508
Total, Fair Value	120,725	136,321
Total, Gross Unrealized Losses	2,068	800
State and political subdivisions
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	758,063	195,285
Less Than 12 Months, Gross Unrealized Losses	28,158	2,891
12 Months or More, Fair Value	26,810	68,361
12 Months or More, Gross Unrealized Losses	975	1,627
Total, Fair Value	784,873	263,646
Total, Gross Unrealized Losses	29,133	4,518
Residential mortgage-backed securities
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	244,239	169,226
Less Than 12 Months, Gross Unrealized Losses	3,992	2,146
12 Months or More, Fair Value	0	3,435
12 Months or More, Gross Unrealized Losses	0	76
Total, Fair Value	244,239	172,661
Total, Gross Unrealized Losses	3,992	2,222
Collateralized mortgage obligations
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	279,001	60,459
Less Than 12 Months, Gross Unrealized Losses	3,778	408
12 Months or More, Fair Value	14,754	39,382
12 Months or More, Gross Unrealized Losses	225	729
Total, Fair Value	293,755	99,841
Total, Gross Unrealized Losses	4,003	1,137
Corporate bonds
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	80,536	9,532
Less Than 12 Months, Gross Unrealized Losses	1,401	200
12 Months or More, Fair Value	0	0
12 Months or More, Gross Unrealized Losses	0	0
Total, Fair Value	80,536	9,532
Total, Gross Unrealized Losses	1,401	200
Trust preferred securities
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	10,699	0
Less Than 12 Months, Gross Unrealized Losses	80	0
12 Months or More, Fair Value	310	300
12 Months or More, Gross Unrealized Losses	190	200
Total, Fair Value	11,009	300
Total, Gross Unrealized Losses	$ 270	$ 200