Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest income
Loans and leases	$ 1,073,051	$ 955,637	$ 876,472
Total investment securities interest and dividend income	150,709	121,207	96,751
Overnight investments	21,997	26,846	14,534
Total interest income	1,245,757	1,103,690	987,757
Interest expense
Deposits	22,483	16,196	18,169
Short-term borrowings	3,657	4,838	1,965
Long-term obligations	10,717	22,760	22,948
Total interest expense	36,857	43,794	43,082
Net interest income (loss)	1,208,900	1,059,896	944,675
Provision for loan and lease losses	28,468	25,692	32,941
Net interest income after provision for loan and lease losses	1,180,432	1,034,204	911,734
Noninterest income
Gain on extinguishment of debt	26,553	12,483	0
ATM income	16,433	23,251	20,348
Insurance commissions	12,702	12,465	11,150
Gain on acquisitions	0	134,745	5,831
ATM income	7,980	9,143	7,283
Securities gains (losses)	351	4,293	26,673
Net impact from FDIC shared-loss termination	0	(45)	16,559
Adjustments to FDIC receivable	(6,341)	(6,232)	(9,725)
Marketable equity securities losses, net	(7,610)	0	0
Other	26,041	35,358	34,170
Total noninterest income	400,149	521,963	377,099
Noninterest expense
Salaries and wages	527,691	490,610	443,746
Employee benefits	118,203	105,975	94,340
Occupancy expense	109,169	104,690	102,609
Equipment expense	102,909	97,478	92,501
Processing Fees Paid to Third Parties	30,017	25,673	18,976
FDIC insurance expense	18,890	22,191	20,967
Foreclosure-related expenses	16,567	14,407	13,379
Merger-related expenses	6,462	9,015	5,341
Other	147,063	142,430	145,907
Total noninterest expense	1,076,971	1,012,469	937,766
Income before income taxes	503,610	543,698	351,067
Income taxes	103,297	219,946	125,585
Net income	$ 400,313	$ 323,752	$ 225,482
Net income per share	$ 33.53	$ 26.96	$ 18.77
Cash dividends (in dollars per share)	$ 1.45	$ 1.25	$ 1.20
Average shares outstanding (in shares)	11,938,439	12,010,405	12,010,405
Service charges on deposit accounts
Noninterest income
Revenue from contracts with customers	$ 105,486	$ 101,201	$ 89,359
Wealth management services
Noninterest income
Revenue from contracts with customers	97,966	86,719	80,221
Cardholder services, net
Noninterest income
Revenue from contracts with customers	65,478	57,583	47,319
Other service charges and fees
Noninterest income
Revenue from contracts with customers	30,606	28,321	27,011
Merchant services, net
Noninterest income
Revenue from contracts with customers	$ 24,504	$ 22,678	$ 20,900