Retirement Benefit Plan - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended
	Apr. 15, 2019	Apr. 03, 2019	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
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			100,669,694		100,669,694
Company's stock held by ESOP			78,398,520		78,896,806
ESOP dividends declared date		Apr. 03, 2019
ESOP dividends declared per share		$ 2.00
ESOP dividends declared amount		$ 52.1
ESOP dividends payment date		May 10, 2019
Common stock dividend ratio	200.00%
Dividends declared date	Apr. 15, 2019
Dividends record date	May 07, 2019
Dividends payment, date	May 08, 2019
Direct Costs of Contracts and Indirect, General and Administrative Expense
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
ESOP contribution expense			$ 14.9	$ 12.2