Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest Income
Interest and Fees on Loans and Leases	$ 370,441	$ 333,239	$ 298,522
Income on Investment Securities
Available-for-Sale	46,772	41,892	41,492
Held-to-Maturity	81,740	79,087	89,650
Deposits	15	9	8
Funds Sold	3,882	2,861	1,133
Other	944	812	1,305
Total Interest Income	503,794	457,900	432,110
Interest Expense
Deposits	22,332	12,647	9,626
Securities Sold Under Agreements to Repurchase	19,592	23,406	25,364
Funds Purchased	123	12	12
Short-term Borrowings	64	0	0
Other Debt	4,445	4,256	3,021
Total Interest Expense	46,556	40,321	38,023
Net Interest Income	457,238	417,579	394,087
Provision for Credit Losses	16,900	4,750	1,000
Net Interest Income After Provision for Credit Losses	440,338	412,829	393,087
Noninterest Income
Trust and Asset Management	45,430	46,203	47,685
Mortgage Banking	12,949	19,895	11,583
Service Charges on Deposit Accounts	32,575	33,654	34,072
Fees, Exchange, and Other Service Charges	54,845	55,176	53,353
Investment Securities Gains (Losses), Net	10,430	10,203	10,160
Annuity and Insurance	6,858	7,017	7,664
Bank-Owned Life Insurance	6,517	6,561	7,039
Other	15,813	18,634	14,663
Total Noninterest Income	185,417	197,343	186,219
Noninterest Expense
Salaries and Benefits	205,536	201,150	191,963
Net Occupancy	32,536	30,252	30,217
Net Equipment	22,078	20,578	20,162
Data Processing	15,483	15,208	16,472
Professional Fees	11,681	10,072	9,660
FDIC Insurance	8,666	8,615	8,669
Other	61,711	64,703	70,961
Total Noninterest Expense	357,691	350,578	348,104
Income Before Provision for Income Taxes	268,064	259,594	231,202
Provision for Income Taxes	83,392	78,133	70,498
Net Income	$ 184,672	$ 181,461	$ 160,704
Basic Earnings Per Share (in dollars per share)	$ 4.37	$ 4.26	$ 3.72
Diluted Earnings Per Share (in dollars per share)	4.33	4.23	3.70
Dividends Declared Per Share (in dollars per share)	$ 2.04	$ 1.89	$ 1.80
Basic Weighted Average Shares (in shares)	42,280,931	42,644,100	43,217,818
Diluted Weighted Average Shares (in shares)	42,607,057	42,879,783	43,454,877