Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Before Tax Amount
Income (loss), before tax amount		$ 40,407	$ 232
Net unrealized gains (losses) on available-for-sale investment securities, before tax amount
Other comprehensive income (loss), securities, available-for-sale, unrealized holding gain (loss) arising during period, before tax		2,194	(4,965)
Recovery of provision for credit losses, before tax		(384)	(597)
Less: reclassification adjustment for net gains on sales realized in net income	[1]	(65)	(695)
Other comprehensive income (loss), securities, available-for-sale, adjustment, before tax		1,745	(5,063)
Net unrealized gains (losses) on interest rate swaps used in cash flow hedges, before tax amount
Net unrealized holding gains (losses) arising during the period		6	(497)
Less: reclassification adjustment for net (gains) losses realized in net income	[2]	76	29
Other comprehensive income (loss), derivatives qualifying as hedges, before tax		82	(468)
Defined benefit pension plans, Before Tax Amount
Amortization of net actuarial loss included in net periodic pension costs	[3]	329	297
Total defined benefit pension plans		329	297
Other comprehensive income (loss), before tax amount		2,156	(5,234)
Total comprehensive income (loss), before tax amount		42,563	(5,002)
Tax Expense (Benefit)
Income tax expense (benefit)		7,804	(606)
Net unrealized gains (losses) on available-for-sale investment securities, tax expense (benefit)
Other comprehensive income (loss), securities, available-for-sale, unrealized holding gain (loss) arising during period, tax		461	(1,042)
Recovery of provision for credit losses, tax		(81)	(125)
Less: reclassification adjustment for net gains on sales realized in net income	[1]	(14)	(146)
Total net unrealized gains (losses) on available-for-sale investment securities		366	(1,063)
Net unrealized gains (losses) on interest rate swaps used in cash flow hedges, tax expense (benefit)
Other comprehensive income (loss), unrealized gain (loss) on derivatives arising during period, tax		1	(104)
Less: reclassification adjustment for net (gains) losses realized in net income	[2]	16	6
Other comprehensive income (loss), derivatives qualifying as hedges, tax		17	(98)
Defined benefit pension plans, tax expense (benefit)
Amortization of net actuarial loss included in net periodic pension costs	[3]	69	62
Other comprehensive (income) loss, defined benefit plan, after reclassification adjustment, tax		69	62
Other comprehensive income (loss), tax expense (benefit)		452	(1,099)
Total comprehensive income (loss), tax expense (benefit)		8,256	(1,705)
Net of Tax Amount
Net income		32,603	838
Net unrealized gains (losses) on available-for-sale investment securities, net of tax amount
Net unrealized holding gains (losses) arising during the period		1,733	(3,923)
Recovery of provision for credit losses, after tax		(303)	(472)
Less: reclassification adjustment for net gains on sales realized in net income	[1]	(51)	(549)
Other comprehensive income (loss), securities, available-for-sale, adjustment, after tax		1,379	(4,000)
Net unrealized gains (losses) on interest rate swaps used in cash flow hedges, net of tax amount
Other comprehensive income (loss), unrealized gain (loss) on derivatives arising during period, net of tax		5	(393)
Less: reclassification adjustment for net (gains) losses realized in net income	[2]	60	23
Total net unrealized gains (losses) on interest rate swaps used in cash flow hedges		65	(370)
Defined benefit pension plans, net of tax amount
Amortization of net actuarial loss included in net periodic pension costs	[3]	260	235
Other comprehensive (income) loss, defined benefit plan, after reclassification adjustment, after tax		260	235
Other comprehensive income (loss), net of tax amount		1,704	(4,135)
Total comprehensive income (loss), net of tax amount		$ 34,307	$ (3,297)

[1] (1) Included in net gain on sales of investment securities on the consolidated statements of income (before tax amount).

[2] (2) Included in interest expense on demand deposits on the consolidated statements of income (before tax amount).

[3] (3) These accumulated other comprehensive loss components are included in the computation of net periodic pension cost (before tax amount). See Note 8, "Retirement Plans and Other Postretirement Benefits" for additional details.