Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Assets
Cash and due from banks	$ 211,174	$ 284,003	$ 192,022
Money market and other interest-earning investments	111,942	33,162	86,219
Total cash and cash equivalents	323,116	317,165	278,241
Equity securities	6,235	5,582	5,569
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	4,569,772	4,123,416	3,219,863
Investment securities - held-to-maturity, at amortized cost (fair value $493,877; $506,103; and $536,143, respectively)	484,834	506,334	535,153
Federal Home Loan Bank/Federal Reserve Bank stock, at cost	157,400	142,980	136,206
Loans held for sale, at fair value	14,082	14,911	17,635
Loans:
Commercial	3,042,790	3,232,970	2,811,629
Commercial real estate	5,023,620	4,958,851	4,449,980
Residential real estate	2,243,885	2,248,404	2,158,532
Consumer credit, net of unearned income	1,758,682	1,803,667	1,818,541
Total loans	12,068,977	12,243,892	11,238,682
Allowance for loan losses	(55,559)	(55,461)	(50,381)
Net loans	12,013,418	12,188,431	11,188,301
Premises and equipment, net	490,216	485,912	453,603
Operating lease right-of-use assets	109,916	0	0
Accrued interest receivable	86,279	89,464	81,621
Goodwill	1,036,258	1,036,258	828,804
Other intangible assets	72,544	77,016	48,833
Company-owned life insurance	444,551	444,224	404,561
Net deferred tax assets	59,430	87,048	88,773
Loan servicing rights	24,254	24,497	24,380
Assets held for sale	5,068	3,253	6,331
Other real estate owned and repossessed personal property	3,279	3,232	6,735
Other assets	183,768	178,712	171,678
Total assets	20,084,420	19,728,435	17,496,287
Deposits:
Noninterest-bearing demand	3,903,314	3,965,380	3,655,732
Interest-bearing:
Checking and NOW	3,742,241	3,788,339	3,135,778
Savings	2,941,361	2,944,092	3,091,101
Money market	1,780,756	1,627,882	1,130,258
Time	2,061,598	2,024,256	1,775,731
Total deposits	14,429,270	14,349,949	12,788,600
Federal funds purchased and interbank borrowings	325,030	270,135	150,026
Securities sold under agreements to repurchase	342,480	362,294	308,189
Federal Home Loan Bank advances	1,719,944	1,613,481	1,664,179
Other borrowings	251,584	247,883	248,898
Operating lease liabilities	114,040	0	0
Accrued expenses and other liabilities	150,200	195,123	157,277
Total liabilities	17,332,548	17,038,865	15,317,169
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, 173,979; 175,141; and 152,172 shares issued and outstanding, respectively	173,979	175,141	152,172
Capital surplus	2,007,962	2,031,695	1,640,776
Retained earnings	567,311	527,684	447,696
Accumulated other comprehensive income (loss), net of tax	2,620	(44,950)	(61,526)
Total shareholders' equity	2,751,872	2,689,570	2,179,118
Total liabilities and shareholders' equity	20,084,420	19,728,435	17,496,287
U.S. Treasury [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	9,777	5,301	9,295
U.S. Government-Sponsored Entities and Agencies [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	698,514	628,151	572,689
Investment securities - held-to-maturity, at amortized cost (fair value $493,877; $506,103; and $536,143, respectively)	74,195	73,986
Mortgage-Backed Securities - Agency [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	2,560,703	2,209,295	1,477,896
Investment securities - held-to-maturity, at amortized cost (fair value $493,877; $506,103; and $536,143, respectively)	123,627	127,120
States and Political Subdivisions [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	965,436	940,429	843,488
Investment securities - held-to-maturity, at amortized cost (fair value $493,877; $506,103; and $536,143, respectively)	287,012	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	$ 335,342	$ 340,240	$ 316,495