Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Assets
Cash and due from banks	$ 184,974	$ 209,381	$ 153,259
Money market and other interest-earning investments	32,061	46,138	22,299
Total cash and cash equivalents	217,035	255,519	175,558
Trading securities, at fair value	5,083	4,982	3,699
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	2,816,943	2,797,174	2,348,443
Investment securities - held-to-maturity, at amortized cost (fair value $784,906; $784,172; and $932,590, respectively)	741,448	745,090	869,012
Federal Home Loan Bank/Federal Reserve Bank stock, at cost	107,501	101,716	86,146
Loans held for sale, at fair value	17,373	90,682	22,546
Loans:
Commercial	1,910,536	1,917,099	1,792,988
Commercial real estate	3,222,865	3,130,853	1,922,754
Residential real estate	2,112,262	2,087,530	1,649,996
Consumer credit, net of unearned income	1,886,110	1,875,030	1,641,336
Total loans	9,131,773	9,010,512	7,007,074
Allowance for loan losses	(49,834)	(49,808)	(50,700)
Net loans	9,081,939	8,960,704	6,956,374
FDIC indemnification asset			7,703
Premises and equipment, net	420,866	429,622	198,065
Accrued interest receivable	76,674	81,381	68,641
Goodwill	655,018	655,018	584,634
Other intangible assets	34,657	37,677	32,443
Company-owned life insurance	353,786	352,956	342,292
Net deferred tax assets	165,376	181,863	98,712
Loan servicing rights	25,446	25,561	10,534
Assets held for sale	14,604	5,970	2,038
Other real estate owned and repossessed personal property	12,547	18,546	13,522
Other assets	123,349	115,776	111,964
Total assets	14,869,645	14,860,237	11,932,326
Deposits:
Noninterest-bearing demand	3,024,111	3,016,093	2,491,767
Interest-bearing:
NOW	2,635,317	2,596,595	2,178,690
Savings	2,997,919	2,954,709	2,271,341
Money market	697,287	707,748	561,250
Time	1,466,718	1,468,108	1,085,847
Total deposits	10,821,352	10,743,253	8,588,895
Federal funds purchased and interbank borrowings	61,016	213,003	165,320
Securities sold under agreements to repurchase	345,550	367,052	379,060
Federal Home Loan Bank advances	1,441,030	1,353,092	899,418
Other borrowings	219,021	218,939	218,393
Accrued expenses and other liabilities	135,317	150,481	172,597
Total liabilities	13,023,286	13,045,820	10,423,683
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, 135,435; 135,159; and 114,352 shares issued and outstanding, respectively	135,435	135,159	114,352
Capital surplus	1,350,866	1,348,338	1,088,037
Retained earnings	408,623	390,292	335,839
Accumulated other comprehensive income (loss), net of tax	(48,565)	(59,372)	(29,585)
Total shareholders' equity	1,846,359	1,814,417	1,508,643
Total liabilities and shareholders' equity	14,869,645	14,860,237	11,932,326
U.S. Treasury [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	12,117	7,103	12,243
U.S. Government-Sponsored Entities and Agencies [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	543,034	493,956	603,457
Mortgage-Backed Securities - Agency [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	1,474,995	1,525,019	990,984
States and Political Subdivisions [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	452,551	436,684	400,236
Other Debt Securities Including Pooled Trust Preferred Securities [Member]
Investment securities - available-for-sale, at fair value:
Total investment securities - available-for-sale	$ 334,246	$ 334,412	$ 341,523