Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Operating Activities
Net Income	$ 52,052	$ 58,799	$ 56,933	$ 54,040	$ 167,770	$ 165,691
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Provision for Credit Losses	4,250		3,800		11,250	11,425
Depreciation and Amortization					12,685	10,512
Amortization of Deferred Loan and Lease Fees					(85)	(330)
Amortization and Accretion of Premiums/Discounts on Investment Securities, Net					15,102	25,633
Amortization of Operating Lease Right-of-Use Assets					9,495	0
Share-Based Compensation					6,662	6,208
Benefit Plan Contributions					(1,472)	(1,352)
Deferred Income Taxes					(5,805)	(6,557)
Gains on Sale of Premises and Equipment					(558)	0
Net Gains on Sales of Loans and Leases					(3,705)	(2,642)
Net Losses (Gains) on Sales of Investment Securities					3,080	3,097
Proceeds from Sales of Loans Held for Sale					299,062	215,897
Originations of Loans Held for Sale					(322,721)	(214,047)
Net Tax Benefits from Share-Based Compensation					693	985
Net Change in Other Assets and Other Liabilities					(38,710)	(5,148)
Net Cash Provided by Operating Activities					152,743	209,372
Investment Securities Available-for-Sale:
Proceeds from Sales, Prepayments and Maturities					1,656,241	287,744
Purchases					(1,203,633)	(147,694)
Investment Securities Held-to-Maturity:
Proceeds from Prepayments and Maturities					518,822	653,488
Purchases					(1,006,455)	(399,346)
Net Change in Loans and Leases					(441,007)	(444,529)
Purchases of Premises and Equipment					(40,381)	(22,514)
Proceeds from Sale of Premises and Equipment					639	0
Net Cash Used in Investing Activities					(515,774)	(72,851)
Financing Activities
Net Change in Deposits					313,510	(40,634)
Net Change in Short-Term Borrowings					99,804	(371)
Repayments of Long-Term Debt					(25,058)	(75,000)
Proceeds from Issuance of Common Stock					6,103	6,233
Repurchase of Common Stock					(107,875)	(66,998)
Cash Dividends Paid					(78,538)	(72,639)
Net Cash Provided by (Used in) Financing Activities					207,946	(249,409)
Net Change in Cash and Cash Equivalents					(155,085)	(112,888)
Cash and Cash Equivalents at Beginning of Period		$ 525,969		$ 447,851	525,969	447,851
Cash and Cash Equivalents at End of Period	370,884		$ 334,963		370,884	334,963
Supplemental Information
Cash Paid for Interest					68,284	44,033
Cash Paid for Income Taxes					43,905	32,403
Non-Cash Investing and Financing Activities:
Initial Recognition of Operating Lease Right-of-Use Assets	101,005				101,005
Initial Recognition of Operating Lease Liabilities	$ 108,264				108,264
Transfer from Investment Securities Held-To-Maturity to Investment Securities Available-For-Sale					1,014,859		$ 0
Transfer from Loans to Foreclosed Real Estate					$ 2,070	$ 2,592