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Retirement Benefit Plan - Additional Information (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Dec. 31, 2020
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items] |  |  |  |  |
Shares fully vested, Description |  |  | Shares allocated to a participant’s account are fully vested after three years of credited service, or in the event(s) of reaching age 65, death or disability while an active employee of the Company. |  |
Shares fully vested after credited service |  |  | 3 years |  |
Common stock shares outstanding including ESOP | 102,257,780 |  | 102,257,780 |  | 102,360,662
Company's stock held by ESOP | 69,719,214 |  | 69,719,214 |  | 76,641,312
Direct Costs of Contracts and Selling, General and Administrative Expense |  |  |  |  |
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items] |  |  |  |  |
ESOP contribution expense | $ 14.8 | $ 12.5 | $ 41.3 | $ 42.0 |

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- Definition The amount of plan compensation cost recognized during the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 40 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=109244661&loc=d3e17540-113929 + Details
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