Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Activities
Net Income	$ 181,461	$ 160,704	$ 163,042
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Provision for Credit Losses	4,750	1,000	(4,864)
Impairment of Equipment Held for Sale	0	9,453	0
Depreciation and Amortization	12,871	12,785	12,442
Amortization of Deferred Loan and Lease Fees	(1,467)	(1,896)	(2,064)
Amortization and Accretion of Premiums/Discounts on Investment Securities, Net	43,728	49,698	50,280
Share-Based Compensation	6,786	7,689	7,870
Benefit Plan Contributions	(1,284)	(1,974)	(1,561)
Deferred Income Taxes	7,187	(6,517)	(5,211)
Net Gains (Losses) on Sale of Loans and Leases	(11,113)	(4,139)	(2,896)
Net Losses (Gains) on Investment Securities	(10,203)	(10,160)	(8,063)
Proceeds from Sales of Loans Held for Sale	273,597	86,338	72,096
Originations of Loans Held for Sale	(280,391)	(81,224)	(68,006)
Tax Benefits from Share-Based Compensation	(1,153)	(1,076)	(670)
Net Change in Other Assets and Other Liabilities	1,760	13,331	(2,915)
Net Cash Provided by Operating Activities	226,529	234,012	209,480
Investment Securities Available-for-Sale:
Proceeds from Prepayments and Maturities	398,405	413,587	325,211
Proceeds from Sales	10,430	67,985	16,574
Purchases	(367,346)	(468,573)	(375,620)
Investment Securities Held-to-Maturity:
Proceeds from Prepayments and Maturities	806,339	979,007	776,876
Purchases	(677,652)	(518,664)	(525,070)
Payments to Acquire Life Insurance Policies	0	0	(35,000)
Net Change in Loans and Leases	(1,263,749)	(1,092,118)	(809,382)
Proceeds from Sale of Loans and Leases Held-for-investment	147,898	101,803	0
Premises and Equipment, Net	(15,177)	(14,130)	(13,660)
Net Cash Provided by (Used in) Investing Activities	(960,852)	(531,103)	(640,071)
Financing Activities
Net Change in Deposits	1,069,137	618,014	718,433
Net Change in Short-Term Borrowings	(103,196)	(60,870)	(82,971)
Proceeds from Long-Term Debt	75,000	175,000	0
Repayments of Other Debt	(50,000)	(100,000)	0
Tax Benefits from Share-Based Compensation	1,153	1,076	670
Proceeds from Issuance of Common Stock	9,079	15,364	9,995
Repurchase of Common Stock	(61,807)	(52,981)	(64,046)
Cash Dividends Paid	(81,157)	(78,367)	(79,660)
Net Cash Provided by (Used in) Financing Activities	858,209	517,236	502,421
Net Change in Cash and Cash Equivalents	123,886	220,145	71,830
Cash and Cash Equivalents at End of Period	879,607	755,721	535,576
Cash and Cash Equivalents at Beginning of Period	755,721	535,576	463,746
Supplemental Information
Cash Paid for Interest	39,482	37,419	36,795
Cash Paid for Income Taxes	57,005	72,740	72,127
Non-Cash Investing and Financing Activities:
Transfer from Loans to Foreclosed Real Estate	1,058	676	3,950
Transfer of Loans to Loans Held for Sale	$ 189,972	$ 101,803	$ 0