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Retirement and Share-based Compensation Plans (Defined Contribution Plan) (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Share-based Payment Arrangement [Abstract] |  |  |
Defined contribution plan, maximum annual employee contribution | $ 19,500 | $ 19,000 | $ 18,500
Defined contribution plan, employer plan contributions | $ 2,400,000 | $ 1,800,000 | $ 1,700,000

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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
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- Definition Maximum amount the employee may contribute to a defined contribution plan. + References No definition available. + Details
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- References No definition available. + Details
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