Consolidated Statements of Comprehensive Income - USD ($)		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Statement of Comprehensive Income [Abstract]
Income before income taxes		$ 88,689,000	$ 97,210,000	$ 114,330,000
Net unrealized gains (losses) on available-for-sale investment securities, before tax amount
Net unrealized holding gains (losses) arising during the period, before tax amount		7,681,000	(49,358,000)	292,000
Provision for credit losses, before tax		(409,000)	211,000	60,000
Less: reclassification adjustment for net gains on sales realized in net income, before tax amount	[1]	0	(30,000)	(145,000)
Total net unrealized gains (losses) on available-for-sale investment securities, before tax amount		7,272,000	(49,177,000)	207,000
Cash flow hedge derivative, before tax amount
Net change in fair value of interest rate swap, before tax amount		(2,726,000)	(7,925,000)	28,000
Less: reclassification adjustment for loss on termination of interest rate swap realized in net income, before tax amount	[2]	5,593,000	(521,000)	304,000
Total cash flow hedge derivative, before tax amount		2,867,000	(8,446,000)	332,000
Defined benefit pension plans, before tax amount
Net unrealized (losses) gains arising during the period, before tax amount		3,380,000	(1,162,000)	5,476,000
Less: amortization of net actuarial loss included in net periodic pension costs, before tax amount	[3]	985,000	873,000	1,316,000
Total defined benefit pension plans, before tax amount		4,365,000	(289,000)	6,792,000
Other comprehensive income (loss), before tax amount		14,504,000	(57,912,000)	7,331,000
Total comprehensive income (loss), before tax amount		103,193,000	39,298,000	121,661,000
Income tax expense		17,585,000	19,090,000	22,529,000
Net unrealized gains (losses) on available-for-sale investment securities, tax expense (benefit)
Net unrealized holding gains (losses) arising during the period, tax expense (benefit)		1,613,000	(10,365,000)	61,000
Provision for credit losses, tax expense (benefit)		(86,000)	44,000	13,000
Less: reclassification adjustment for net gains on sales realized in net income, tax expense (benefit)	[1]	0	(6,000)	(30,000)
Total net unrealized gains (losses) on available-for-sale investment securities, tax expense (benefit)		1,527,000	(10,327,000)	44,000
Cash flow hedge derivative, tax expense (benefit)
Net change in fair value of interest rate swap, tax expense (benefit)		(573,000)	(1,665,000)	6,000
Less: reclassification adjustment for loss on termination of interest rate swap realized in net income, tax expense (benefit)	[2]	1,175,000	(109,000)	64,000
Total cash flow hedge derivative, tax expense (benefit)		602,000	(1,774,000)	70,000
Defined benefit pension plans, tax expense (benefit)
Net unrealized (losses) gains arising during the period, tax expense (benefit)		710,000	(244,000)	1,150,000
Less: amortization of net actuarial loss included in net periodic pension costs, tax expense (benefit)	[3]	207,000	184,000	276,000
Total defined benefit pension plans, tax expense (benefit)		917,000	(60,000)	1,426,000
Other comprehensive income (loss), tax expense (benefit)		3,046,000	(12,161,000)	1,540,000
Total comprehensive income (loss), tax expense (benefit)		20,631,000	6,929,000	24,069,000
Net income		71,104,000	78,120,000	91,801,000
Net unrealized gains (losses) on available-for-sale investment securities, net of tax amount
Net unrealized holding gains (losses) arising during the period, net of tax amount		6,068,000	(38,993,000)	231,000
Provision for credit losses, net of tax		(323,000)	167,000	47,000
Less: reclassification adjustment for net gains on sales realized in net income, net of tax amount	[1]	0	(24,000)	(115,000)
Total net unrealized gains (losses) on available-for-sale investment securities, net of tax amount		5,745,000	(38,850,000)	163,000
Cash flow hedge derivative, net of tax amount
Net change in fair value of interest rate swap, net of tax amount		(2,153,000)	(6,260,000)	22,000
Less: reclassification adjustment for loss on termination of interest rate swap realized in net income, net of tax amount	[2]	4,418,000	(412,000)	240,000
Total cash flow hedge derivative, net of tax amount		2,265,000	(6,672,000)	262,000
Defined benefit pension plans, net of tax amount
Net unrealized (losses) gains arising during the period, net of tax amount		2,670,000	(918,000)	4,326,000
Less: amortization of net actuarial loss included in net periodic pension costs, net of tax amount	[3]	778,000	689,000	1,040,000
Total defined benefit pension plans, net of tax amount		3,448,000	(229,000)	5,366,000
Other comprehensive income (loss)		11,458,000	(45,751,000)	5,791,000
Total comprehensive income (loss), net of tax amount		$ 82,562,000	$ 32,369,000	$ 97,592,000

[1] (1) Included in net gain on sales of investment securities on the consolidated statements of income (before tax amount).

[2] (2) Included in interest expense on demand deposits on the consolidated statements of income (before tax amount).

[3] (3) These accumulated other comprehensive loss components are included in the computation of net periodic pension cost (before tax amount). See Note 13, "Retirement Plans and Other Postretirement Benefits" for additional details.