Components of Accumulated Other Comprehensive Income - Changes in Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Changes in accumulated other comprehensive income by component
Balance at beginning of the period	$ 1,583,571	$ 1,538,703	$ 1,353,285
Other comprehensive income/(loss) before reclassification adjustments	(133,004)	(5,125)	1,464
Amounts reclassified from accumulated other comprehensive income	(525)	1,045	1,928
Other comprehensive income/(loss)	(133,529)	(4,080)	3,392
Balance at end of the period	1,491,486	1,583,571	1,538,703
Unrealized holding gains and losses, tax	(45,321)	(10,333)	5,607
Unrealized holding losses, tax	0	0	(209)
Unrealized holding losses, tax	7,182	9,144	(4,169)
Realized gains, tax	0	(92)	(6)
Realized interest rate swaps, tax	0	0	209
Realized gains, tax	(202)	515	395
Cumulative Effect, Period of Adoption, Adjustment
Changes in accumulated other comprehensive income by component
Balance at beginning of the period			(9,649)
Accumulated other comprehensive loss
Changes in accumulated other comprehensive income by component
Balance at beginning of the period	(37,629)	(33,549)	(36,941)
Balance at end of the period	(171,158)	(37,629)	(33,549)
Unrealized gain/(loss) on marketable securities available-for-sale
Changes in accumulated other comprehensive income by component
Balance at beginning of the period	(12,317)	16,843	3,147
Other comprehensive income/(loss) before reclassification adjustments	(151,888)	(28,873)	13,711
Amounts reclassified from accumulated other comprehensive income	(1)	(287)	(15)
Other comprehensive income/(loss)	(151,889)	(29,160)	13,696
Balance at end of the period	(164,206)	(12,317)	16,843
Change in fair value of interest rate swaps
Changes in accumulated other comprehensive income by component
Balance at beginning of the period		0	0
Other comprehensive income/(loss) before reclassification adjustments			(946)
Amounts reclassified from accumulated other comprehensive income			946
Other comprehensive income/(loss)			0
Balance at end of the period			0
Defined benefit pension plans
Changes in accumulated other comprehensive income by component
Balance at beginning of the period	(25,312)	(50,392)	(40,088)
Other comprehensive income/(loss) before reclassification adjustments	18,884	23,748	(11,301)
Amounts reclassified from accumulated other comprehensive income	(524)	1,332	997
Other comprehensive income/(loss)	18,360	25,080	(10,304)
Balance at end of the period	$ (6,952)	$ (25,312)	$ (50,392)

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of increase (decrease) in accumulated other comprehensive income.

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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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Amount of tax expense (benefit) for (increase) decrease in value of benefit obligation for change in actuarial assumptions and increase (decrease) in value of plan assets from experience different from that assumed of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

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Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.

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