Revenue from Contracts with Customers (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Personal trust and agency accounts	$ 2,637,000	$ 2,290,000	$ 7,650,000	$ 6,550,000
Employee benefit and retirement-related accounts	2,506,000	1,967,000	7,170,000	5,702,000
Investment management and investment advisory agency accounts	3,220,000	2,695,000	9,345,000	7,852,000
Other	457,000	383,000	1,397,000	1,137,000
Non-sufficient funds (NSF) fees	1,498,000	1,201,000	3,776,000	3,644,000
Demand deposit account (DDA) charges	762,000	787,000	2,325,000	2,289,000
Other	129,000	130,000	374,000	389,000
Credit card	692,000	488,000	1,908,000	1,548,000
HELOC	100,000	108,000	288,000	319,000
Installment	34,000	43,000	114,000	144,000
Real estate	5,418,000	11,806,000	19,867,000	22,228,000
Commercial	424,000	602,000	1,267,000	1,332,000
Debit card fee income	6,453,000	5,853,000	19,297,000	16,373,000
Bank owned life insurance income	1,462,000	1,192,000	3,776,000	3,619,000
ATM Fees	622,000	491,000	1,807,000	1,341,000
Gains (Losses) on Sales of Other Real Estate	3,000	569,000	(26,000)	1,214,000
(Gain) loss on equity securities, net	609,000	1,201,000	2,886,000	(749,000)
Other components of net periodic benefit income	2,038,000	1,988,000	6,114,000	5,964,000
Other	3,347,000	2,791,000	8,403,000	5,826,000
Total other income	32,411,000	36,558,000	97,738,000	90,008,000
Debt Securities, Realized Gain (Loss)	0	(27,000)	0	3,286,000
Bank Servicing [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	6,668,000	13,047,000	23,444,000	25,571,000
Within Scope [Domain]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	1,300,000	1,300,000	3,800,000	3,700,000
Out of Scope [Domain]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	5,400,000	11,700,000	19,600,000	21,900,000
PNB [Member]
Disaggregation of Revenue [Line Items]
Personal trust and agency accounts	2,637,000	2,290,000	7,650,000	6,550,000
Employee benefit and retirement-related accounts	2,506,000	1,967,000	7,170,000	5,702,000
Investment management and investment advisory agency accounts	3,220,000	2,695,000	9,345,000	7,852,000
Other	457,000	383,000	1,397,000	1,137,000
Non-sufficient funds (NSF) fees	1,498,000	1,201,000	3,776,000	3,644,000
Demand deposit account (DDA) charges	762,000	787,000	2,325,000	2,289,000
Other	129,000	130,000	374,000	389,000
Credit card	690,000	487,000	1,906,000	1,544,000
HELOC	100,000	108,000	288,000	319,000
Installment	34,000	43,000	114,000	144,000
Real estate	5,418,000	11,806,000	19,867,000	22,228,000
Commercial	281,000	567,000	1,063,000	1,245,000
Debit card fee income	6,453,000	5,853,000	19,297,000	16,373,000
Bank owned life insurance income	1,022,000	1,109,000	3,169,000	3,452,000
ATM Fees	622,000	491,000	1,807,000	1,341,000
Gains (Losses) on Sales of Other Real Estate	3,000	198,000	(26,000)	843,000
(Gain) loss on equity securities, net	429,000	739,000	1,758,000	113,000
Other components of net periodic benefit income	1,987,000	1,940,000	5,960,000	5,820,000
Other	3,084,000	2,663,000	8,018,000	5,649,000
Total other income	31,332,000	35,430,000	95,258,000	89,920,000
Debt Securities, Realized Gain (Loss)		(27,000)		3,286,000
All Other [Member]
Disaggregation of Revenue [Line Items]
Personal trust and agency accounts	0	0	0	0
Employee benefit and retirement-related accounts	0	0	0	0
Investment management and investment advisory agency accounts	0	0	0	0
Other	0	0	0	0
Non-sufficient funds (NSF) fees	0	0	0	0
Demand deposit account (DDA) charges	0	0	0	0
Other	0	0	0	0
Credit card	2,000	1,000	2,000	4,000
HELOC	0	0	0	0
Installment	0	0	0	0
Real estate	0	0	0	0
Commercial	143,000	35,000	204,000	87,000
Debit card fee income	0	0	0	0
Bank owned life insurance income	440,000	83,000	607,000	167,000
ATM Fees	0	0	0	0
Gains (Losses) on Sales of Other Real Estate	0	371,000	0	371,000
(Gain) loss on equity securities, net	180,000	462,000	1,128,000	(862,000)
Other components of net periodic benefit income	51,000	48,000	154,000	144,000
Other	263,000	128,000	385,000	177,000
Total other income	$ 1,079,000	1,128,000	$ 2,480,000	88,000
Debt Securities, Realized Gain (Loss)		$ 0		$ 0