Shareholders' Equity - Net Change in Components of Accumulated Other Comprehensive Income (Loss) and the Related Tax Effects (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax amount	$ (77,982)	$ 7,819	$ (232,777)	$ (12,787)
Other comprehensive income (loss), tax (expense) benefit	19,496	1,954	58,195	(3,197)
Other comprehensive income (loss), before reclassifications, net of tax amount			(175,088)	10,306
Reclassification from accumulated other comprehensive income, current period, net of tax amount			506	716
Other comprehensive income (loss), net of tax amount	(58,486)	5,865	(174,582)	(9,590)
Securities Available for Sale and Transferred Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, before tax amount	(44,529)	6,612	(200,200)	(15,188)
Other comprehensive income (loss), change in net unrealized holding loss on securities transferred to held to maturity, before tax amount	(33,784)	736	(33,251)	1,447
Other comprehensive income (loss), before tax amount	(78,313)	7,348	(233,451)	(13,741)
Other comprehensive income (loss), before reclassifications, tax (expense) benefit	11,132	1,653	(50,050)	(3,797)
Other comprehensive income (loss), change in net unrealized holding loss on securities transferred to held to maturity, tax (expense) benefit	8,446	184	(8,313)	362
Other comprehensive income (loss), tax (expense) benefit	19,578	1,837	(58,363)	(3,435)
Other comprehensive income (loss), before reclassifications, net of tax amount	(33,397)	4,959	(150,150)	(11,391)
Other comprehensive income (loss), change in net unrealized holding loss on securities transferred to held to maturity, net of tax amount	(25,338)	552	(24,938)	1,085
Other comprehensive income (loss), net of tax amount	(58,735)	5,511	(175,088)	(10,306)
Net Change in Prior Service Costs [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from accumulated other comprehensive income, current period, before tax amount	27	28	55	56
Reclassification from accumulated other comprehensive income, current period, tax (expense) benefit	(6)	(7)	(14)	(14)
Reclassification from accumulated other comprehensive income, current period, net of tax amount	21	21	41	(42)
Change in Net Actuarial Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from accumulated other comprehensive income, current period, before tax amount	304	443	619	898
Reclassification from accumulated other comprehensive income, current period, tax (expense) benefit	(76)	(110)	(154)	(224)
Reclassification from accumulated other comprehensive income, current period, net of tax amount	(228)	(333)	(465)	(674)
Pension and Other Postretirement Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from accumulated other comprehensive income, current period, before tax amount	(331)	(471)	(674)	(954)
Reclassification from accumulated other comprehensive income, current period, tax (expense) benefit	(82)	(117)	(168)	(238)
Reclassification from accumulated other comprehensive income, current period, net of tax amount	$ (249)	$ (354)	$ (506)	$ (716)