Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Assets
Cash and due from banks	$ 320,822	$ 284,003	$ 215,024
Money market and other interest-earning investments	99,428	33,162	71,737
Total cash and cash equivalents	420,250	317,165	286,761
Equity securities	6,562	5,582	5,828
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	4,916,979	4,123,416	3,272,456
Investment securities - held-to-maturity, at amortized cost (fair value $425,588; $506,103; and $505,566, respectively)	407,281	506,334	512,207
Federal Home Loan Bank/Federal Reserve Bank stock, at cost	164,101	142,980	136,206
Loans held for sale, at fair value	58,285	14,911	21,384
Loans:
Total loans	12,017,648	12,243,892	11,292,659
Allowance for loan losses	(56,910)	(55,461)	(52,713)
Net loans	11,960,738	12,188,431	11,239,946
Premises and equipment, net	492,065	485,912	450,253
Operating lease right-of-use assets	102,976	0	0
Accrued interest receivable	80,747	89,464	78,493
Goodwill	1,036,994	1,036,258	828,804
Other intangible assets	64,051	77,016	42,134
Company-owned life insurance	447,110	444,224	405,245
Net deferred tax assets	26,523	87,048	94,667
Loan servicing rights	24,623	24,497	24,336
Other assets	229,503	185,197	169,039
Total assets	20,438,788	19,728,435	17,567,759
Deposits:
Noninterest-bearing demand	3,996,264	3,965,380	3,588,370
Interest-bearing:
Checking and NOW	3,936,318	3,788,339	3,011,544
Savings	2,863,718	2,944,092	2,920,712
Money market	1,821,989	1,627,882	1,185,439
Time	1,830,063	2,024,256	1,892,135
Total deposits	14,448,352	14,349,949	12,598,200
Federal funds purchased and interbank borrowings	240,589	270,135	450,031
Securities sold under agreements to repurchase	337,551	362,294	319,831
Federal Home Loan Bank advances	2,001,960	1,613,481	1,554,515
Other borrowings	251,763	247,883	251,662
Operating lease liabilities	107,272	0	0
Accrued expenses and other liabilities	218,771	195,123	172,840
Total liabilities	17,606,258	17,038,865	15,347,079
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, 170,031; 175,141; and 152,352 shares issued and outstanding, respectively	170,031	175,141	152,352
Capital surplus	1,948,808	2,031,695	1,645,111
Retained earnings	655,177	527,684	503,147
Accumulated other comprehensive income (loss), net of tax	58,514	(44,950)	(79,930)
Total shareholders' equity	2,832,530	2,689,570	2,220,680
Total liabilities and shareholders' equity	20,438,788	19,728,435	17,567,759
U.S. Treasury [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	5,494	5,301	5,237
U.S. Government-Sponsored Entities and Agencies [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	486,104	628,151	611,696
Investment securities - held-to-maturity, at amortized cost (fair value $425,588; $506,103; and $505,566, respectively)	33,321	73,986
Mortgage-Backed Securities - Agency [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	3,136,180	2,209,295	1,508,692
Investment securities - held-to-maturity, at amortized cost (fair value $425,588; $506,103; and $505,566, respectively)	112,187	127,120
States and Political Subdivisions [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	969,475	940,429	792,666
Investment securities - held-to-maturity, at amortized cost (fair value $425,588; $506,103; and $505,566, respectively)	261,773	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	319,726	340,240	354,165
Commercial Loan [Member]
Loans:
Total loans	2,950,559	3,232,970	2,949,277
Allowance for loan losses	(22,129)	(21,742)	(19,719)
Commercial Real Estate [Member]
Loans:
Total loans	5,112,123	4,958,851	4,481,554
Allowance for loan losses	(24,254)	(23,470)	(22,892)
Consumer Loan [Member]
Loans:
Total loans	1,718,343	1,803,667	1,695,625
Allowance for loan losses	(8,164)	(7,972)	(8,182)
Residential Real Estate [Member]
Loans:
Total loans	$ 2,236,623	$ 2,248,404	$ 2,166,203