Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Assets
Cash and due from banks	$ 234,766	$ 284,003
Money market and other interest-earning investments	41,571	33,162
Total cash and cash equivalents	276,337	317,165
Equity securities	6,842	5,582
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	5,385,091	4,123,416
Investment securities - held-to-maturity, at amortized cost (fair value $0 and $506,103, respectively)		506,334
Federal Home Loan Bank/Federal Reserve Bank stock, at cost	164,099	142,980
Loans held for sale, at fair value	46,898	14,911
Loans:
Total loans	12,117,524	12,243,892
Allowance for loan losses	(54,619)	(55,461)
Net loans	12,062,905	12,188,431
Premises and equipment, net	490,925	485,912
Operating lease right-of-use assets	95,477
Accrued interest receivable	85,123	89,464
Goodwill	1,036,994	1,036,258
Other intangible assets	60,105	77,016
Company-owned life insurance	448,967	444,224
Net deferred tax assets	29,705	87,048
Loan servicing rights	25,368	24,497
Other assets	196,831	185,197
Total assets	20,411,667	19,728,435
Deposits:
Noninterest-bearing demand	4,042,286	3,965,380
Interest-bearing:
Checking and NOW	4,149,639	3,788,339
Savings	2,845,423	2,944,092
Money market	1,833,819	1,627,882
Time	1,682,230	2,024,256
Total deposits	14,553,397	14,349,949
Federal funds purchased and interbank borrowings	350,414	270,135
Securities sold under agreements to repurchase	327,782	362,294
Federal Home Loan Bank advances	1,822,847	1,613,481
Other borrowings	243,685	247,883
Operating lease liabilities	99,500
Accrued expenses and other liabilities	161,589	195,123
Total liabilities	17,559,214	17,038,865
Commitments and contingencies (Note 23)
Shareholders' Equity
Preferred stock, series A, 2,000 shares authorized, no shares issued or outstanding
Common stock, $1.00 per share stated value, 300,000 shares authorized, 169,616 and 175,141 shares issued and outstanding, respectively	169,616	175,141
Capital surplus	1,944,445	2,031,695
Retained earnings	682,185	527,684
Accumulated other comprehensive income (loss), net of tax	56,207	(44,950)
Total shareholders' equity	2,852,453	2,689,570
Total liabilities and shareholders' equity	20,411,667	19,728,435
U.S. Treasury [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	17,682	5,301
U.S. Government-Sponsored Entities and Agencies [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	592,984	628,151
Investment securities - held-to-maturity, at amortized cost (fair value $0 and $506,103, respectively)		73,986
Mortgage-Backed Securities - Agency [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	3,183,861	2,209,295
Investment securities - held-to-maturity, at amortized cost (fair value $0 and $506,103, respectively)		127,120
States and Political Subdivisions [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	1,275,643	940,429
Investment securities - held-to-maturity, at amortized cost (fair value $0 and $506,103, respectively)		305,228
Other Debt Securities Including Pooled Trust Preferred Securities [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	314,921	340,240
Commercial Loan [Member]
Loans:
Total loans	2,890,296	3,232,970
Allowance for loan losses	(22,585)	(21,742)
Commercial Real Estate [Member]
Loans:
Total loans	5,166,792	4,958,851
Allowance for loan losses	(21,588)	(23,470)
Consumer Loan [Member]
Loans:
Total loans	1,726,147	1,803,667
Allowance for loan losses	(8,147)	(7,972)
Residential Real Estate [Member]
Loans:
Total loans	$ 2,334,289	$ 2,248,404