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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