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Retirement Benefit Plan - Additional Information (Details) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2021 | Mar. 31, 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 | 102,406,446 |  | 102,360,662
Company's stock held by ESOP | 75,560,749 |  | 76,641,312
Direct Costs of Contracts and Selling, General and Administrative Expense |  |  |
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items] |  |  |
ESOP contribution expense | $ 13.2 | $ 14.9 |

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