Accumulated Other Comprehensive Income (Loss) - Reclassifications out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of unrealized gains and losses		$ 312	$ 394	$ 1,118	$ 730
Tax benefit (expense)		(4,977)	(3,783)	(12,614)	(7,071)
Realized net gain on sale of securities		1,381	78	3,399	8,281
Total reclassifications for the period, net of tax		(681)	(2,150)	(2,726)	2,418
Unrealized gains (losses)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassified from accumulated other comprehensive income		1,069	(316)	2,281	7,551
Realized net gain (loss) on interest rate swap derivatives
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassified from accumulated other comprehensive income		(1,617)	(1,587)	(4,784)	(2,283)
Net actuarial loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassified from accumulated other comprehensive income	[1]	(316)	(821)	(948)	(2,213)
Prior service credit
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassified from accumulated other comprehensive income	[1]	0	2	0	6
Amortization of pension plan
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassified from accumulated other comprehensive income		(316)	(819)	(948)	(2,207)
Tax benefit		67	172	199	463
Total reclassifications for the period, net of tax		(249)	(647)	(749)	(1,744)
Unrealized gains and losses on securities transferred | Reclassification out of accumulated other comprehensive income | Unrealized gains (losses)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of unrealized gains and losses	[2]	(312)	(394)	(1,118)	(730)
Tax benefit (expense)		66	82	235	153
Net of tax		(246)	(312)	(883)	(577)
Unrealized gains and losses on available for sale securities | Reclassification out of accumulated other comprehensive income | Unrealized gains (losses)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax benefit (expense)		(290)	(16)	(714)	(1,739)
Net of tax		1,091	62	2,685	6,542
Realized net gain on sale of securities	[3]	1,381	78	3,399	8,281
Interest rate swap derivatives | Reclassification out of accumulated other comprehensive income | Realized net gain (loss) on interest rate swap derivatives
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax benefit (expense)		340	335	1,005	484
Net of tax		(1,277)	(1,258)	(3,779)	(1,819)
Realized net (loss) gain on interest rate swap derivatives	[4]	(1,617)	(1,593)	(4,784)	(2,303)
Interest rate swap derivatives | Reclassification out of accumulated other comprehensive income | Amortization of unrealized gains on terminated interest rate swap derivatives
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax benefit (expense)		0	(1)	0	(4)
Net of tax		0	5	0	16
Realized net (loss) gain on interest rate swap derivatives	[4]	$ 0	$ 6	$ 0	$ 20

[1] These AOCI components are included in the computation of net periodic pension cost (income) presented in “Note 8 – Employee Benefit Plans.”

[2] Included in interest income on the consolidated statements of income.

[3] Listed as net gain on sale of securities AFS on the consolidated statements of income.

[4] Included in interest expense for FHLB borrowings on the consolidated statements of income.