Accumulated Other Comprehensive Income (Loss) - Changes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pre-tax Amount
Other comprehensive income (loss), Pre-tax Amount	$ (209,065)	$ 86,548	$ 137,465
Income Tax Benefit (Expense)
Other comprehensive income (loss), Income Tax Benefit (Expense)	55,768	(23,195)	(37,019)
Net of tax
Balance	2,744,104	2,640,258	2,524,839
Other comprehensive (loss) income	(153,297)	63,353	100,446
Balance	2,656,912	2,744,104	2,640,258
Accumulated Other Comprehensive Income (Loss)
Pre-tax Amount
Accumulated other comprehensive income (loss), beginning balance, Pre-tax Amount	43,098	(43,450)	(180,915)
Accumulated other comprehensive (loss) income, ending balance, Pre-tax Amount	(165,967)	43,098	(43,450)
Income Tax Benefit (Expense)
Accumulated other comprehensive income (loss), beginning balance, Income Tax Benefit (Expense)	(11,494)	11,701	48,720
Accumulated other comprehensive loss, ending balance, Income Tax Benefit (Expense)	44,274	(11,494)	11,701
Net of tax
Balance	31,604	(31,749)	(132,195)
Other comprehensive (loss) income	(153,297)	63,353	100,446
Balance	(121,693)	31,604	(31,749)
Unfunded Pension Liability
Pre-tax Amount
Unrealized net gains (losses) arising during the period, Pre-tax Amount	10,020	(4,855)	407
Income Tax Benefit (Expense)
Unrealized net losses (gains) arising during the period, Income Tax Benefit (Expense)	(2,673)	1,200	(110)
Net of tax
Balance	(31,737)	(28,082)	(28,379)
Unrealized net (losses) gains arising during the period, Net of tax	7,347	(3,655)	297
Other comprehensive (loss) income	7,347	(3,655)	297
Balance	(24,390)	(31,737)	(28,082)
Pension and other benefits, net actuarial losses arising during the period
Pre-tax Amount
Unrealized net gains (losses) arising during the period, Pre-tax Amount	3,107	(10,399)	(5,774)
Income Tax Benefit (Expense)
Unrealized net losses (gains) arising during the period, Income Tax Benefit (Expense)	(829)	2,774	1,555
Net of tax
Unrealized net (losses) gains arising during the period, Net of tax	2,278	(7,625)	(4,219)
Pension and other benefits, prior service credit
Pre-tax Amount
Unrealized net gains (losses) arising during the period, Pre-tax Amount		(51)	(429)
Income Tax Benefit (Expense)
Unrealized net losses (gains) arising during the period, Income Tax Benefit (Expense)		14	115
Net of tax
Unrealized net (losses) gains arising during the period, Net of tax		(37)	(314)
Pension and other benefits: Amortization of net loss included in net income
Pre-tax Amount
Unrealized net gains (losses) arising during the period, Pre-tax Amount	6,913	5,595	6,610
Income Tax Benefit (Expense)
Unrealized net losses (gains) arising during the period, Income Tax Benefit (Expense)	(1,844)	(1,492)	(1,780)
Net of tax
Unrealized net (losses) gains arising during the period, Net of tax	5,069	4,103	4,830
Pension and other benefits, change in Company tax rate
Income Tax Benefit (Expense)
Unrealized net losses (gains) arising during the period, Income Tax Benefit (Expense)		(96)
Unrealized Loss on Securities
Pre-tax Amount
Unrealized net gains (losses) arising during the period, Pre-tax Amount			137,058
Reclassification of net losses (gains) to net income, Pre-tax Amount		114	2,715
Other comprehensive income (loss), Pre-tax Amount	(219,085)	91,403
Income Tax Benefit (Expense)
Unrealized net losses (gains) arising during the period, Income Tax Benefit (Expense)			(36,909)
Reclassification of net gains (losses) to net income, Income Tax Benefit (Expense)		30	731
Other comprehensive income (loss), Income Tax Benefit (Expense)	58,441	(24,395)
Net of tax
Balance	63,341	(3,667)	(103,816)
Unrealized net (losses) gains arising during the period, Net of tax			100,149
Reclassification of net (gains) losses to net income, Net of tax		84	1,984
Other comprehensive (loss) income	(160,644)	67,008	100,149
Balance	(97,303)	63,341	(3,667)
Investment securities: Unrealized net gains arising during the year
Pre-tax Amount
Unrealized net gains (losses) arising during the period, Pre-tax Amount	(218,983)	91,289	134,343
Income Tax Benefit (Expense)
Unrealized net losses (gains) arising during the period, Income Tax Benefit (Expense)	58,414	(24,365)	(36,178)
Net of tax
Unrealized net (losses) gains arising during the period, Net of tax	(160,569)	$ 66,924	$ 98,165
Investment securities: Investment securities losses, net
Pre-tax Amount
Reclassification of net losses (gains) to net income, Pre-tax Amount	(102)
Income Tax Benefit (Expense)
Reclassification of net gains (losses) to net income, Income Tax Benefit (Expense)	(27)
Net of tax
Reclassification of net (gains) losses to net income, Net of tax	$ (75)