Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Before Tax Amount
Income (loss), before tax amount		$ 1,821	$ 20,137	$ 2,053	$ 39,715
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		7,169	2,933	2,204	8,053
Recovery of provision for credit losses, before tax		(42)
Provision for credit losses, before tax				555
Less: reclassification adjustment for net gains on sales realized in net income	[1]	(65)	(7)	(760)	(8)
Other comprehensive income (loss), securities, available-for-sale, adjustment, before tax		7,062	2,926	1,999	8,045
Net unrealized gains (losses) on interest rate swaps used in cash flow hedges, before tax amount
Net unrealized holding losses arising during the period		(62)	(263)	(559)	(431)
Less: reclassification adjustment for net (gains) losses realized in net income	[2]	69	(14)	98	(30)
Other comprehensive income (loss), derivatives qualifying as hedges, before tax		7	(277)	(461)	(461)
Defined benefit pension plans, Before Tax Amount
Amortization of net actuarial loss included in net periodic pension costs	[3]	297	294	594	588
Accretion of prior service cost included in net periodic pension costs	[3]	0	(46)	0	(91)
Total defined benefit pension plans		297	248	594	497
Other comprehensive income (loss), before tax amount		7,366	2,897	2,132	8,081
Total comprehensive income (loss), before tax amount		9,187	23,034	4,185	47,796
Tax Expense (Benefit)
Income tax (benefit) expense		(264)	3,669	(870)	7,168
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		1,504	616	462	1,691
Recovery of provision for credit losses, tax		(8)
Provision for credit losses, tax				117
Less: reclassification adjustment for net gains on sales realized in net income	[1]	(14)	(2)	(160)	(2)
Total net unrealized gains on available-for-sale investment securities		1,482	614	419	1,689
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		(13)	(55)	(118)	(91)
Less: reclassification adjustment for net (gains) losses realized in net income	[2]	14	(3)	21	(6)
Other comprehensive income (loss), derivatives qualifying as hedges, tax		1	(58)	(97)	(97)
Defined benefit pension plans, tax expense (benefit)
Amortization of net actuarial loss included in net periodic pension costs	[3]	62	62	124	124
Accretion of prior service cost included in net periodic pension costs	[3]	0	(10)	0	(19)
Other comprehensive (income) loss, defined benefit plan, after reclassification adjustment, tax		62	52	124	105
Other comprehensive income (loss), tax expense (benefit)		1,545	608	446	1,697
Total comprehensive income (loss), tax expense (benefit)		1,281	4,277	(424)	8,865
Net of Tax Amount
Net income		2,085	16,468	2,923	32,547
Net unrealized gains (losses) on available-for-sale investment securities, net of tax amount
Net unrealized holding gains arising during the period		5,665	2,317	1,742	6,362
Recovery of provision for credit losses, after tax		(34)
Provision for credit losses, after tax				438
Less: reclassification adjustment for net gains on sales realized in net income	[1]	(51)	(5)	(600)	(6)
Other comprehensive income (loss), securities, available-for-sale, adjustment, after tax		5,580	2,312	1,580	6,356
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		(49)	(208)	(441)	(340)
Less: reclassification adjustment for net (gains) losses realized in net income	[2]	55	(11)	77	(24)
Total net unrealized gains (losses) on interest rate swaps used in cash flow hedges		6	(219)	(364)	(364)
Defined benefit pension plans, net of tax amount
Amortization of net actuarial loss included in net periodic pension costs	[3]	235	232	470	464
Accretion of prior service cost included in net periodic pension costs	[3]	0	(36)	0	(72)
Other comprehensive (income) loss, defined benefit plan, after reclassification adjustment, after tax		235	196	470	392
Other comprehensive income (loss), net of tax amount		5,821	2,289	1,686	6,384
Total comprehensive income (loss), net of tax amount		$ 7,906	$ 18,757	$ 4,609	$ 38,931

[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 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.