Investment Securities (Summary of Investment Securities with Gross Unrealized Losses) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	$ 1,078,804	$ 1,379,705
Less Than 12 Months, Gross Unrealized Losses	16,485	21,534
12 Months or More, Fair Value	1,605,905	563,188
12 Months or More, Gross Unrealized Losses	44,904	13,649
Total, Fair Value	2,684,709	1,942,893
Total, Gross Unrealized Losses	61,389	35,183
Government and government-sponsored enterprises
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	167,164	63,818
Less Than 12 Months, Gross Unrealized Losses	1,672	510
12 Months or More, Fair Value	62,200	24,621
12 Months or More, Gross Unrealized Losses	1,683	438
Total, Fair Value	229,364	88,439
Total, Gross Unrealized Losses	3,355	948
State and political subdivisions
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	190,551	437,407
Less Than 12 Months, Gross Unrealized Losses	1,932	12,268
12 Months or More, Fair Value	657,327	349,242
12 Months or More, Gross Unrealized Losses	14,016	10,093
Total, Fair Value	847,878	786,649
Total, Gross Unrealized Losses	15,948	22,361
Residential mortgage-backed securities
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	20,679	93,508
Less Than 12 Months, Gross Unrealized Losses	85	383
12 Months or More, Fair Value	123,757	56,576
12 Months or More, Gross Unrealized Losses	3,738	1,243
Total, Fair Value	144,436	150,084
Total, Gross Unrealized Losses	3,823	1,626
Collateralized mortgage obligations
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	496,356	713,525
Less Than 12 Months, Gross Unrealized Losses	5,268	7,235
12 Months or More, Fair Value	656,208	73,707
12 Months or More, Gross Unrealized Losses	19,752	1,249
Total, Fair Value	1,152,564	787,232
Total, Gross Unrealized Losses	25,020	8,484
Corporate bonds
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	169,431	71,447
Less Than 12 Months, Gross Unrealized Losses	5,888	1,138
12 Months or More, Fair Value	103,688	47,878
12 Months or More, Gross Unrealized Losses	5,551	454
Total, Fair Value	273,119	119,325
Total, Gross Unrealized Losses	11,439	1,592
Trust preferred securities
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	34,623	0
Less Than 12 Months, Gross Unrealized Losses	1,640	0
12 Months or More, Fair Value	2,725	11,164
12 Months or More, Gross Unrealized Losses	164	172
Total, Fair Value	37,348	11,164
Total, Gross Unrealized Losses	$ 1,804	$ 172