Consolidated Balance Sheets - USD ($) $ in Thousands		Mar. 31, 2020	Dec. 31, 2019
Assets
Cash and due from banks		$ 203,533	$ 234,766
Money market and other interest-earning investments		139,644	41,571
Total cash and cash equivalents		343,177	276,337
Equity securities		6,870	6,842
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale		5,360,025	5,385,091
Federal Home Loan Bank/Federal Reserve Bank stock, at cost		174,113	164,099
Loans held for sale, at fair value		54,209	46,898
Loans:
Total loans		12,384,612	12,117,524
Allowance for loan losses	[1]	(106,380)	(54,619)
Net loans		12,278,232	12,062,905
Premises and equipment, net		462,364	490,925
Operating lease right-of-use assets		86,819	95,477
Accrued interest receivable		77,810	85,123
Goodwill		1,036,994	1,036,994
Other intangible assets		56,329	60,105
Company-owned life insurance		450,148	448,967
Net deferred tax assets		17,576	29,705
Loan servicing rights		24,132	25,368
Other assets		312,343	196,831
Total assets		20,741,141	20,411,667
Deposits:
Noninterest-bearing demand		4,058,559	4,042,286
Interest-bearing:
Checking and NOW		4,105,006	4,149,639
Savings		2,853,305	2,845,423
Money market		1,746,798	1,833,819
Time		1,541,694	1,682,230
Total deposits		14,305,362	14,553,397
Federal funds purchased and interbank borrowings		560,770	350,414
Securities sold under agreements to repurchase		318,067	327,782
Federal Home Loan Bank advances		2,130,263	1,822,847
Other borrowings		236,114	243,685
Operating lease liabilities		95,830	99,500
Accrued expenses and other liabilities		271,300	161,589
Total liabilities		17,917,706	17,559,214
Shareholders' Equity
Preferred stock, 2,000 shares authorized, no shares issued or outstanding		0	0
Common stock, $1.00 per share stated value, 300,000 shares authorized,    165,109 and 169,616 shares issued and outstanding, respectively		165,109	169,616
Capital surplus		1,870,260	1,944,445
Retained earnings		649,909	682,185
Accumulated other comprehensive income (loss), net of tax		138,157	56,207
Total shareholders' equity		2,823,435	2,852,453
Total liabilities and shareholders' equity		20,741,141	20,411,667
U.S. Treasury
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale		11,733	17,682
U.S. government-sponsored entities and agencies
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale		519,171	592,984
Mortgage-backed securities
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale		3,210,000	3,183,861
States and political subdivisions
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale		1,302,395	1,275,643
Other securities
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale		316,726	314,921
Commercial Loan
Loans:
Total loans		3,046,579	2,890,296
Commercial Real Estate Loan
Loans:
Total loans		5,283,464	5,166,792
Consumer Loan
Loans:
Total loans		1,726,718	1,726,147
Residential Real Estate Loan
Loans:
Total loans		$ 2,327,851	$ 2,334,289

[1] Beginning January 1, 2020, calculation is based on current expected loss methodology. Prior to January 1, 2020, calculation was based on incurred loss methodology.