Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Assets
Cash and due from banks	$ 239,831	$ 284,003	$ 219,626
Money market and other interest-earning investments	61,155	33,162	54,248
Total cash and cash equivalents	300,986	317,165	273,874
Equity securities	6,234	5,582	5,596
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	4,667,226	4,123,416	3,181,665
Investment securities - held-to-maturity, at amortized cost (fair value $486,728; $506,103; and $524,597, respectively)	470,868	506,334	525,718
Federal Home Loan Bank/Federal Reserve Bank stock, at cost	157,400	142,980	136,206
Loans held for sale, at fair value	37,904	14,911	26,198
Loans:
Total loans	12,046,578	12,243,892	11,295,629
Allowance for loan losses	(56,292)	(55,461)	(53,660)
Net loans	11,990,286	12,188,431	11,241,969
Premises and equipment, net	493,481	485,912	449,304
Operating lease right-of-use assets	106,222	0	0
Accrued interest receivable	90,543	89,464	81,290
Goodwill	1,036,258	1,036,258	828,804
Other intangible assets	68,220	77,016	45,417
Company-owned life insurance	445,749	444,224	405,492
Net deferred tax assets	36,002	87,048	90,187
Loan servicing rights	24,332	24,497	24,303
Other assets	213,574	185,197	166,967
Total assets	20,145,285	19,728,435	17,482,990
Deposits:
Noninterest-bearing demand	3,771,888	3,965,380	3,600,793
Interest-bearing:
Checking and NOW	3,950,161	3,788,339	3,054,302
Savings	2,877,673	2,944,092	3,026,110
Money market	1,819,716	1,627,882	1,090,621
Time	1,943,663	2,024,256	1,824,550
Total deposits	14,363,101	14,349,949	12,596,376
Federal funds purchased and interbank borrowings	410,036	270,135	175,044
Securities sold under agreements to repurchase	334,540	362,294	347,511
Federal Home Loan Bank advances	1,730,065	1,613,481	1,757,308
Other borrowings	251,840	247,883	250,241
Operating lease liabilities	110,596	0	0
Accrued expenses and other liabilities	141,968	195,123	156,295
Total liabilities	17,342,146	17,038,865	15,282,775
Shareholders' Equity
Preferred stock, 2,000 shares authorized, no shares issued or outstanding	0	0	0
Common stock, $1.00 per share stated value, 300,000 shares authorized, 172,231; 175,141; and 152,351 shares issued and outstanding, respectively	172,231	175,141	152,351
Capital surplus	1,981,205	2,031,695	1,642,790
Retained earnings	607,666	527,684	471,777
Accumulated other comprehensive income (loss), net of tax	42,037	(44,950)	(66,703)
Total shareholders' equity	2,803,139	2,689,570	2,200,215
Total liabilities and shareholders' equity	20,145,285	19,728,435	17,482,990
U.S. Treasury [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	5,466	5,301	5,257
U.S. Government-Sponsored Entities and Agencies [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	645,458	628,151	568,231
Investment securities - held-to-maturity, at amortized cost (fair value $486,728; $506,103; and $524,597, respectively)	74,403	73,986
Mortgage-Backed Securities - Agency [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	2,781,515	2,209,295	1,448,526
Investment securities - held-to-maturity, at amortized cost (fair value $486,728; $506,103; and $524,597, respectively)	118,720	127,120
States and Political Subdivisions [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	908,566	940,429	797,533
Investment securities - held-to-maturity, at amortized cost (fair value $486,728; $506,103; and $524,597, respectively)	277,745	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	326,221	340,240	362,118
Commercial Loan [Member]
Loans:
Total loans	3,074,849	3,232,970	2,962,895
Allowance for loan losses	(22,548)	(21,742)	(21,387)
Commercial Real Estate [Member]
Loans:
Total loans	4,993,693	4,958,851	4,451,772
Allowance for loan losses	(23,311)	(23,470)	(22,498)
Consumer Loan [Member]
Loans:
Total loans	1,755,838	1,803,667	1,726,989
Allowance for loan losses	(8,164)	(7,972)	(7,908)
Residential Real Estate [Member]
Loans:
Total loans	$ 2,222,198	$ 2,248,404	$ 2,153,973