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Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held.

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Amount of benefit for defined benefit plan expected to be paid in five fiscal years after fifth fiscal year following current fiscal year.

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Amount of benefit for defined benefit plan expected to be paid in next fiscal year following current fiscal year.

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Amount of benefit for defined benefit plan expected to be paid in fifth fiscal year following current fiscal year.

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Amount of benefit for defined benefit plan expected to be paid in fourth fiscal year following current fiscal year.

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Amount of benefit for defined benefit plan expected to be paid in third fiscal year following current fiscal year.

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Amount of benefit for defined benefit plan expected to be paid in second fiscal year following current fiscal year.

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Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Retirement Plans - Fair Value Measurements and Expected Benefit Payments for Defined Benefit Pension Plans (Details) - Defined Benefit Pension Plans - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Total plan assets, net	$ 829,420	$ 710,663	$ 964,289
Expected benefit payments for defined benefit pension plans
2021	21,387
2022	21,461
2023	21,677
2024	22,347
2025	23,065
2026 — 2030	125,302
Plan assets measured at fair value, net
Defined Benefit Plan Disclosure [Line Items]
Total plan assets, net	827,913	710,073
Plan assets measured at fair value, net \| Common Stock
Defined Benefit Plan Disclosure [Line Items]
Total plan assets, net	5,252	5,346
Plan assets measured at fair value, net \| Common or collective trusts - Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Total plan assets, net	230,135	215,904
Plan assets measured at fair value, net \| Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Total plan assets, net	532	493
Plan assets measured at fair value, net \| Government securities
Defined Benefit Plan Disclosure [Line Items]
Total plan assets, net	12,036	12,962
Plan assets measured at fair value, net \| Common or collective trusts - Debt securities
Defined Benefit Plan Disclosure [Line Items]
Total plan assets, net	507,691	412,416
Plan assets measured at fair value, net \| Guaranteed investment contracts
Defined Benefit Plan Disclosure [Line Items]
Total plan assets, net	20,588	19,650
Plan assets measured at fair value, net \| Common or collective trusts - Other
Defined Benefit Plan Disclosure [Line Items]
Total plan assets, net	51,679	43,302
Plan assets not measured at fair value, net
Defined Benefit Plan Disclosure [Line Items]
Total plan assets, net	1,507	590
Level 1 \| Plan assets measured at fair value, net
Defined Benefit Plan Disclosure [Line Items]
Total plan assets, net	5,252	5,346
Level 1 \| Plan assets measured at fair value, net \| Common Stock
Defined Benefit Plan Disclosure [Line Items]
Total plan assets, net	5,252	5,346
Level 2 \| Plan assets measured at fair value, net
Defined Benefit Plan Disclosure [Line Items]
Total plan assets, net	802,073	685,077
Level 2 \| Plan assets measured at fair value, net \| Common or collective trusts - Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Total plan assets, net	230,135	215,904
Level 2 \| Plan assets measured at fair value, net \| Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Total plan assets, net	532	493
Level 2 \| Plan assets measured at fair value, net \| Government securities
Defined Benefit Plan Disclosure [Line Items]
Total plan assets, net	12,036	12,962
Level 2 \| Plan assets measured at fair value, net \| Common or collective trusts - Debt securities
Defined Benefit Plan Disclosure [Line Items]
Total plan assets, net	507,691	412,416
Level 2 \| Plan assets measured at fair value, net \| Common or collective trusts - Other
Defined Benefit Plan Disclosure [Line Items]
Total plan assets, net	51,679	43,302
Level 3
Reconciliation of the beginning and ending balances of the fair value measurements using significant unobservable inputs (Level 3):
Balance at beginning of year	19,650	374,724
Actual return on plan assets: Assets still held at reporting date	2,092	1,609
Actual return on plan assets: Assets sold during the period	0	49,524
Purchases	343	187
Settlements	(1,497)	(406,394)
Balance at end of year	20,588	19,650
Level 3 \| Plan assets measured at fair value, net
Defined Benefit Plan Disclosure [Line Items]
Total plan assets, net	20,588	19,650
Level 3 \| Plan assets measured at fair value, net \| Guaranteed investment contracts
Defined Benefit Plan Disclosure [Line Items]
Total plan assets, net	$ 20,588	$ 19,650