Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Activities
Net Income	$ 184,672	$ 181,461	$ 160,704
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Provision for Credit Losses	16,900	4,750	1,000
Impairment of Equipment Held for Sale	0	0	9,453
Depreciation and Amortization	13,048	12,871	12,785
Amortization of Deferred Loan and Lease Fees	(1,031)	(1,467)	(1,896)
Amortization and Accretion of Premiums/Discounts on Investment Securities, Net	39,186	43,728	49,698
Share-Based Compensation	7,369	6,786	7,689
Benefit Plan Contributions	(11,454)	(1,284)	(1,974)
Deferred Income Taxes	4,177	7,187	(6,517)
Net Gains (Losses) on Sale of Loans and Leases	(6,780)	(11,113)	(4,139)
Net Losses (Gains) on Investment Securities	(10,430)	(10,203)	(10,160)
Proceeds from Sales of Loans Held for Sale	323,784	273,597	86,338
Originations of Loans Held for Sale	(326,195)	(280,391)	(81,224)
Net Tax Benefits from Share-based Compensation	2,521	0	0
Tax Benefits from Share-Based Compensation	0	(1,153)	(1,076)
Net Change in Other Assets and Other Liabilities	(60,622)	1,760	13,331
Net Cash Provided by Operating Activities	175,145	226,529	234,012
Investment Securities Available-for-Sale:
Proceeds from Prepayments and Maturities	354,804	398,405	413,587
Proceeds from Sales	10,435	10,430	67,985
Purchases	(427,061)	(367,346)	(468,573)
Investment Securities Held-to-Maturity:
Proceeds from Prepayments and Maturities	882,748	806,339	979,007
Purchases	(995,076)	(677,652)	(518,664)
Net Change in Loans and Leases	(954,984)	(1,263,749)	(1,092,118)
Proceeds from Sale of Loans and Leases Held-for-investment	137,717	147,898	101,803
Premises and Equipment, Net	(30,470)	(15,177)	(14,130)
Net Cash Provided by (Used in) Investing Activities	(1,021,887)	(960,852)	(531,103)
Financing Activities
Net Change in Deposits	563,728	1,069,137	618,014
Net Change in Short-Term Borrowings	(27,701)	(103,196)	(60,870)
Proceeds from Long-Term Debt	0	75,000	175,000
Repayments of Other Debt	0	(50,000)	(100,000)
Tax Benefits from Share-Based Compensation	0	1,153	1,076
Proceeds from Issuance of Common Stock	13,101	9,079	15,364
Repurchase of Common Stock	(47,076)	(61,807)	(52,981)
Cash Dividends Paid	(87,066)	(81,157)	(78,367)
Net Cash Provided by (Used in) Financing Activities	414,986	858,209	517,236
Net Change in Cash and Cash Equivalents	(431,756)	123,886	220,145
Cash and Cash Equivalents at End of Period	447,851	879,607	755,721
Cash and Cash Equivalents at Beginning of Period	879,607	755,721	535,576
Supplemental Information
Cash Paid for Interest	44,945	39,482	37,419
Cash Paid for Income Taxes	67,883	57,005	72,740
Non-Cash Investing and Financing Activities:
Transfer from Loans to Foreclosed Real Estate	2,559	1,058	676
Transfer of Loans to Loans Held for Sale	$ 86,625	$ 189,972	$ 101,803