Retirement Plans - Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Equity mutual funds
Defined Benefit Plans
Target allocation percentage of investments	12.00%
Fixed income mutual funds
Defined Benefit Plans
Target allocation percentage of investments	88.00%
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans
Fair value of plan assets	$ 165.6	$ 163.2
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Cash
Defined Benefit Plans
Fair value of plan assets	0.6	0.6
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Equity mutual funds
Defined Benefit Plans
Fair value of plan assets	19.4	20.6
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fixed income mutual funds
Defined Benefit Plans
Fair value of plan assets	$ 145.6	$ 142.0

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- Definition

Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- Definition

Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(5)(i)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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