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Employee Benefit Plans - Defined Contribution Retirement Plans (Details) - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
The DC Plan
Defined Contribution Retirement Plans
Maximum voluntary contribution by eligible U.S. employees as a percentage of their compensation	50.00%
Number of shares contributed	276	287	279
Compensation expense	$ 11.3	$ 10.3	$ 9.4
Supplemental Retirement Savings Plan (SRSP)
Defined Contribution Retirement Plans
Compensation expense	0.2	0.2	$ 0.3
Supplemental Retirement Savings Plan (SRSP) | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Contribution Retirement Plans
Fair value of assets	$ 20.9	$ 20.4

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- Definition

Defined Contribution Plan, Fair Value of Plan Assets

+ References

No definition available.

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- Definition

Represents the number of shares contributed by the entity under the defined contribution plan.

+ References

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- Definition

Amount of cost for defined contribution plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

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- Definition

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No definition available.

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- Definition

Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

+ References

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