Consolidated Statements of Comprehensive Income - USD ($)		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Statement of Comprehensive Income [Abstract]
Income before income taxes		$ 114,330,000	$ 56,897,000	$ 80,053,000
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		292,000	2,346,000	10,168,000
Provision for credit losses, before tax		60,000	569,000	0
Less: reclassification adjustment for net gains on sales realized in net income, before tax amount	[1]	(145,000)	(871,000)	(54,000)
Total net unrealized gains (losses) on available-for-sale investment securities, before tax amount		207,000	2,044,000	10,114,000
Cash flow hedge derivative, before tax amount
Net change in fair value of interest rate swap, before tax amount		28,000	(553,000)	(420,000)
Less: reclassification adjustment for loss on termination of interest rate swap realized in net income, before tax amount	[2]	304,000	254,000	(22,000)
Total cash flow hedge derivative, before tax amount		332,000	(299,000)	(442,000)
Defined benefit pension plans, before tax amount
Net unrealized (losses) gains arising during the period, before tax amount		5,476,000	(3,772,000)	(2,308,000)
Less: amortization of net actuarial loss included in net periodic pension costs, before tax amount	[3]	1,316,000	1,202,000	1,176,000
Less: accretion of prior service cost included in net periodic pension costs, before tax amount	[3]	0	0	(181,000)
Total defined benefit pension plans, before tax amount		6,792,000	(2,570,000)	(1,313,000)
Other comprehensive income (loss), before tax amount		7,331,000	(825,000)	8,359,000
Total comprehensive income (loss), before tax amount		121,661,000	56,072,000	88,412,000
Income tax expense		22,529,000	9,981,000	14,334,000
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)		61,000	493,000	2,135,000
Provision for credit losses, tax expense (benefit)		13,000	119,000	0
Less: reclassification adjustment for net gains on sales realized in net income, tax expense (benefit)	[1]	(30,000)	(183,000)	(11,000)
Total net unrealized gains (losses) on available-for-sale investment securities, tax expense (benefit)		44,000	429,000	2,124,000
Cash flow hedge derivative, tax expense (benefit)
Net change in fair value of interest rate swap, tax expense (benefit)		6,000	(116,000)	(88,000)
Less: reclassification adjustment for loss on termination of interest rate swap realized in net income, tax expense (benefit)	[2]	64,000	53,000	(5,000)
Total cash flow hedge derivative, tax expense (benefit)		70,000	(63,000)	(93,000)
Defined benefit pension plans, tax expense (benefit)
Net unrealized (losses) gains arising during the period, tax expense (benefit)		1,150,000	(792,000)	(485,000)
Less: amortization of net actuarial loss included in net periodic pension costs, tax expense (benefit)	[3]	276,000	252,000	248,000
Less: accretion of prior service cost included in net periodic pension costs, tax expense (benefit)	[3]	0	0	(38,000)
Total defined benefit pension plans, tax expense (benefit)		1,426,000	(540,000)	(275,000)
Other comprehensive income (loss), tax expense (benefit)		1,540,000	(174,000)	1,756,000
Total comprehensive income (loss), tax expense (benefit)		24,069,000	9,807,000	16,090,000
Net income		91,801,000	46,916,000	65,719,000
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		231,000	1,853,000	8,033,000
Provision for credit losses, net of tax		47,000	450,000	0
Less: reclassification adjustment for net gains on sales realized in net income, net of tax amount	[1]	(115,000)	(688,000)	(43,000)
Total net unrealized gains (losses) on available-for-sale investment securities, net of tax amount		163,000	1,615,000	7,990,000
Cash flow hedge derivative, net of tax amount
Net change in fair value of interest rate swap, net of tax amount		22,000	(437,000)	(332,000)
Less: reclassification adjustment for loss on termination of interest rate swap realized in net income, net of tax amount	[2]	240,000	201,000	(17,000)
Total cash flow hedge derivative, net of tax amount		262,000	(236,000)	(349,000)
Defined benefit pension plans, net of tax amount
Net unrealized (losses) gains arising during the period, net of tax amount		4,326,000	(2,980,000)	(1,823,000)
Less: amortization of net actuarial loss included in net periodic pension costs, net of tax amount	[3]	1,040,000	950,000	928,000
Less: accretion of prior service cost included in net periodic pension costs, net of tax amount	[3]	0	0	(143,000)
Total defined benefit pension plans, net of tax amount		5,366,000	(2,030,000)	(1,038,000)
Other comprehensive income (loss)		5,791,000	(651,000)	6,603,000
Total comprehensive income (loss), net of tax amount		$ 97,592,000	$ 46,265,000	$ 72,322,000

[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.