Consolidated Condensed Statements Of Income - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Interest and dividend income:
Interest and fees on loans	$ 81,176,000	$ 80,155,000	$ 159,913,000	$ 160,842,000
Interest and dividends on:
Obligations of U.S. Government, its agencies and other securities	4,600,000	5,026,000	8,856,000	10,557,000
Interest Income, Securities, State and Municipal	2,032,000	2,151,000	4,069,000	4,351,000
Other interest income	186,000	113,000	329,000	604,000
Total interest and dividend income	87,994,000	87,445,000	173,167,000	176,354,000
Interest on deposits:
Demand and savings deposits	401,000	1,507,000	787,000	7,849,000
Time deposits	1,285,000	3,346,000	2,869,000	7,631,000
Interest on borrowings:
Short-term borrowings	182,000	233,000	365,000	695,000
Long-term debt	2,275,000	1,173,000	4,561,000	2,710,000
Total interest expense	4,143,000	6,259,000	8,582,000	18,885,000
Net interest income	83,851,000	81,186,000	164,585,000	157,469,000
(Recovery of) provision for credit losses	(4,040,000)	12,224,000	(8,895,000)	17,377,000
Net interest income after provision for credit losses	87,891,000	68,962,000	173,480,000	140,092,000
Noninterest Income [Abstract]
Debit card fee income	6,758,000	5,560,000	12,844,000	10,520,000
Bank owned life insurance income	1,149,000	1,179,000	2,314,000	2,427,000
ATM Fees	655,000	438,000	1,185,000	850,000
Gains (Losses) on Sales of Other Real Estate	4,000	841,000	(29,000)	645,000
Debt Securities, Realized Gain (Loss)	0	3,313,000	0	3,313,000
(Gain) loss on equity securities, net	467,000	(977,000)	2,277,000	(1,950,000)
Other components of net periodic benefit income	2,038,000	1,988,000	4,076,000	3,976,000
Other	2,407,000	1,395,000	5,056,000	3,035,000
Total other income	31,238,000	30,964,000	65,327,000	53,450,000
Other expense:
Salaries and employee benefits	30,303,000	30,699,000	60,199,000	59,128,000
Employee Benefits and Share-based Compensation	10,056,000	9,080,000	20,257,000	19,123,000
Occupancy expense	3,027,000	3,256,000	6,667,000	6,736,000
Furniture and equipment expense	2,756,000	4,850,000	5,366,000	9,169,000
Data processing fees	7,150,000	2,577,000	14,862,000	5,069,000
Professional fees and services	6,973,000	6,901,000	12,637,000	13,967,000
Marketing	1,290,000	1,136,000	2,781,000	2,622,000
Insurance	1,276,000	1,477,000	2,967,000	3,027,000
Communication	770,000	874,000	1,892,000	2,029,000
Excise and Sales Taxes	1,103,000	1,116,000	2,211,000	2,261,000
Amortization of Intangible Assets	479,000	607,000	958,000	1,213,000
Payment for Debt Extinguishment or Debt Prepayment Cost	0	0	0	1,793,000
Foundation contribution expense	4,000,000	0	4,000,000	0
Other expense	2,217,000	2,226,000	4,468,000	4,938,000
Total other expense	71,400,000	64,799,000	139,265,000	131,075,000
Income before income taxes	47,729,000	35,127,000	99,542,000	62,467,000
Income taxes	8,597,000	5,622,000	17,579,000	10,590,000
Net income	$ 39,132,000	$ 29,505,000	$ 81,963,000	$ 51,877,000
Net income available to common shareholders
Basic	$ 2.39	$ 1.81	$ 5.02	$ 3.18
Diluted	$ 2.38	$ 1.80	$ 4.98	$ 3.16
Weighted average common shares outstanding
Basic	16,340,690	16,296,427	16,327,838	16,300,015
Diluted	16,472,800	16,375,434	16,455,673	16,400,657
Cash dividends declared	$ 1.03	$ 1.02	$ 2.26	$ 2.24
Fiduciary and Trust [Member]
Noninterest Income [Abstract]
Revenue from Contract with Customer, Including Assessed Tax	$ 8,569,000	$ 6,793,000	$ 16,742,000	$ 13,906,000
Deposit Account [Member]
Noninterest Income [Abstract]
Revenue from Contract with Customer, Including Assessed Tax	2,032,000	1,676,000	4,086,000	4,204,000
Bank Servicing [Member]
Noninterest Income [Abstract]
Revenue from Contract with Customer, Including Assessed Tax	$ 7,159,000	$ 8,758,000	$ 16,776,000	$ 12,524,000