Retirement Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Plan contributions	$ 0.1	$ 0.1	$ 0.2	$ 0.2
Postretirement Medical Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans
Plan contributions	$ 0.1	$ 0.2	$ 0.3	$ 0.4

Amount of contribution received by defined benefit plan from employer which increases plan assets.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
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Name:	us-gaap_DefinedBenefitPlanContributionsByEmployer
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration