Retirement and Other Employee Benefits - Narrative (Details) - USD ($)	9 Months Ended	12 Months Ended
Sep. 30, 2021	Dec. 31, 2020	Feb. 29, 2020
Defined Benefit Plan Disclosure [Line Items]
Qualified pension benefits plan funded status	$ 56,600,000	$ 43,200,000
Funded status percentage	107.00%	105.00%
Cash contribution to qualified pension benefits plan	$ 0
Cash expected contribution to plan over remainder of fiscal year	$ 0
Retirement Health Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate (as a percentage)			1.55%
Reduction in obligations		$ 65,600,000

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

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-Publisher FASB
-Name Accounting Standards Codification
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Amount of contribution expected to be received by defined benefit plan from employer in remainder of current fiscal year. Excludes contribution previously paid by employer in current fiscal year.

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Percentage of plan assets to benefit obligation of defined benefit plan.

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Amount of funded (unfunded) status of defined benefit plan, measured as difference between fair value of plan assets and benefit obligation. Includes, but is not limited to, overfunded (underfunded) status.

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Amount of increase (decrease) in benefit obligation of defined benefit plan from change in terms of existing plan or initiation of new plan.

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Amount of cash outflow for pension benefit. Includes, but is not limited to, employer contribution to fund plan asset and payment to retiree. Excludes other postretirement benefit.

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