Significant Accounting Policies (Details)	12 Months Ended
Dec. 31, 2020 USD ($) Payment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Home office and equipment [Abstract]
Accumulated depreciation of home office and equipment	$ 51,200,000	$ 43,000,000.0	$ 38,100,000
Depreciation expense of home office and equipment	$ 6,300,000	6,500,000	6,000,000.0
Minimum number of payments past due to be in default \| Payment	2
Maximum age for qualified employees for both medical and dental benefits	65 years
Related party transaction amount		$ 0	$ 0
Minimum
Home office and equipment [Abstract]
Estimated useful life	3 years
Award vesting period	1 year
Maximum
Home office and equipment [Abstract]
Estimated useful life	45 years
Award vesting period	3 years

The number of payments past due in order for such loans to be considered in default.

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Postretirement Benefits Liability, Maximum Age For Qualified Employees

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- Definition

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
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The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Amount of transactions with related party during the financial reporting period.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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