Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Assets
Cash and due from banks	$ 215,024	$ 222,753	$ 202,652
Money market and other interest-earning investments	71,737	67,679	49,715
Total cash and cash equivalents	286,761	290,432	252,367
Trading securities, at fair value	5,828	5,584	5,351
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	3,272,456	3,196,207	2,775,837
Investment securities - held-to-maturity, at amortized cost (fair value $505,566; $727,703; and $740,564, respectively)	512,207	684,063	688,951
Federal Home Loan Bank/Federal Reserve Bank stock, at cost	136,206	119,686	117,354
Loans held for sale, at fair value	21,384	17,930	30,221
Loans:
Commercial	2,949,277	2,717,269	2,049,054
Commercial real estate	4,481,554	4,354,552	3,370,211
Residential real estate	2,166,203	2,167,053	2,119,120
Consumer credit, net of unearned income	1,695,625	1,879,247	1,859,739
Total loans	11,292,659	11,118,121	9,398,124
Allowance for loan losses	(52,713)	(50,381)	(50,169)
Net loans	11,239,946	11,067,740	9,347,955
Premises and equipment, net	450,253	458,074	412,488
Accrued interest receivable	78,493	87,102	75,342
Goodwill	828,804	828,051	655,018
Other intangible assets	42,134	53,096	29,235
Company-owned life insurance	405,245	403,753	356,897
Net deferred tax assets	94,667	110,857	137,951
Loan servicing rights	24,336	24,661	24,900
Assets held for sale	9,381	7,180	8,196
Other real estate owned and repossessed personal property	3,563	8,810	10,259
Other assets	156,095	155,066	137,478
Total assets	17,567,759	17,518,292	15,065,800
Deposits:
Noninterest-bearing demand	3,588,370	3,680,807	3,034,696
Interest-bearing:
Checking and NOW	3,011,544	3,115,822	2,539,233
Savings	2,920,712	3,035,622	2,932,488
Money market	1,185,439	1,139,077	648,378
Time	1,892,135	1,634,436	1,451,989
Total deposits	12,598,200	12,605,764	10,606,784
Federal funds purchased and interbank borrowings	450,031	335,033	317,021
Securities sold under agreements to repurchase	319,831	384,810	285,409
Federal Home Loan Bank advances	1,554,515	1,609,579	1,589,367
Other borrowings	251,662	248,782	219,314
Accrued expenses and other liabilities	172,840	179,927	141,082
Total liabilities	15,347,079	15,363,895	13,158,977
Shareholders' Equity
Preferred stock, 2,000 shares authorized, no shares issued or outstanding
Common stock, $1.00 per share stated value, 300,000 shares authorized, 152,352; 152,040; and 135,523 shares issued and outstanding, respectively	152,352	152,040	135,523
Capital surplus	1,645,111	1,639,499	1,354,036
Retained earnings	503,147	413,130	451,461
Accumulated other comprehensive income (loss), net of tax	(79,930)	(50,272)	(34,197)
Total shareholders' equity	2,220,680	2,154,397	1,906,823
Total liabilities and shareholders' equity	17,567,759	17,518,292	15,065,800
U.S. Treasury [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	5,237	5,551	5,615
U.S. Government-Sponsored Entities and Agencies [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	611,696	664,286	576,436
Investment securities - held-to-maturity, at amortized cost (fair value $505,566; $727,703; and $740,564, respectively)	73,776
Mortgage-Backed Securities - Agency [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	1,508,692	1,667,682	1,450,736
Investment securities - held-to-maturity, at amortized cost (fair value $505,566; $727,703; and $740,564, respectively)	131,562	6,903
States and Political Subdivisions [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	792,666	530,193	414,673
Investment securities - held-to-maturity, at amortized cost (fair value $505,566; $727,703; and $740,564, respectively)	306,869	677,160
Other Debt Securities Including Pooled Trust Preferred Securities [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	$ 354,165	$ 328,495	$ 328,377