Shareholders' Equity - Net Change in Components of Accumulated Other Comprehensive Income (Loss) and the Related Tax Effects (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax amount	$ (154,795)	$ 20,606
Other comprehensive income (loss), tax (expense) benefit	38,699	(5,151)
Other comprehensive income (loss), before reclassifications, net of tax amount	(116,353)	15,817
Reclassification from accumulated other comprehensive income, current period, net of tax amount	257	362
Other comprehensive income (loss), net of tax amount	(116,096)	(15,455)
Securities Available for Sale and Transferred Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, before tax amount	(155,671)	21,800
Other comprehensive income (loss), change in net unrealized holding loss on securities transferred to held to maturity, before tax amount	533	711
Other comprehensive income (loss), before tax amount	(155,138)	21,089
Other comprehensive income (loss), before reclassifications, tax (expense) benefit	38,918	(5,450)
Other comprehensive income (loss), change in net unrealized holding loss on securities transferred to held to maturity, tax (expense) benefit	(133)	(178)
Other comprehensive income (loss), tax (expense) benefit	38,785	(5,272)
Other comprehensive income (loss), before reclassifications, net of tax amount	(116,753)	16,350
Other comprehensive income (loss), change in net unrealized holding loss on securities transferred to held to maturity, net of tax amount	400	533
Other comprehensive income (loss), net of tax amount	(116,353)	15,817
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	28	28
Reclassification from accumulated other comprehensive income, current period, tax (expense) benefit	(8)	(7)
Reclassification from accumulated other comprehensive income, current period, net of tax amount	20	21
Recognized Net Loss Due to Lump Sum Settlements [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from accumulated other comprehensive income, current period, before tax amount	0	0
Reclassification from accumulated other comprehensive income, current period, tax (expense) benefit	(0)	(0)
Reclassification from accumulated other comprehensive income, current period, net of tax amount	0	0
Change in Net Actuarial Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from accumulated other comprehensive income, current period, before tax amount	315	455
Reclassification from accumulated other comprehensive income, current period, tax (expense) benefit	(78)	(114)
Reclassification from accumulated other comprehensive income, current period, net of tax amount	237	341
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	343	483
Reclassification from accumulated other comprehensive income, current period, tax (expense) benefit	(86)	(121)
Reclassification from accumulated other comprehensive income, current period, net of tax amount	$ 257	$ 362