Employee Benefits - Plan Assets and Investment Policy (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Employee Benefits
Weighted-average asset allocations (as a percent)	100.00%	100.00%
Target allocation
Fair value of plan assets	$ 70.2	$ 72.4
Level 1
Target allocation
Fair value of plan assets	50.3	52.6
Level 2
Target allocation
Fair value of plan assets	19.9	19.8
Equity securities
Target allocation
Fair value of plan assets	24.8	26.6
Equity securities \| Level 1
Target allocation
Fair value of plan assets	24.8	26.6
U.S. government, state, and agency
Target allocation
Fair value of plan assets	7.9	7.1
U.S. government, state, and agency \| Level 2
Target allocation
Fair value of plan assets	7.9	7.1
Corporate debt securities
Target allocation
Fair value of plan assets	9.7	10.0
Corporate debt securities \| Level 2
Target allocation
Fair value of plan assets	9.7	10.0
Mutual funds
Target allocation
Fair value of plan assets	23.4	25.3
Mutual funds \| Level 1
Target allocation
Fair value of plan assets	21.1	22.6
Mutual funds \| Level 2
Target allocation
Fair value of plan assets	2.3	2.7
Interest and non-interest bearing cash
Target allocation
Fair value of plan assets	4.4	3.4
Interest and non-interest bearing cash \| Level 1
Target allocation
Fair value of plan assets	$ 4.4	$ 3.4
Equity securities
Employee Benefits
Weighted-average asset allocations (as a percent)	56.00%	58.00%
Target allocation
Target allocation, minimum (as a percent)	50.00%
Target allocation, maximum (as a percent)	80.00%
Debt securities
Employee Benefits
Weighted-average asset allocations (as a percent)	38.00%	37.00%
Target allocation
Target allocation, minimum (as a percent)	20.00%
Target allocation, maximum (as a percent)	60.00%
Other
Employee Benefits
Weighted-average asset allocations (as a percent)	6.00%	5.00%
Target allocation
Target allocation, minimum (as a percent)	0.00%
Target allocation, maximum (as a percent)	10.00%

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No definition available.

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Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 30
-Section 35
-Paragraph 50
-URI http://asc.fasb.org/extlink&oid=49178875&loc=d3e12355-114930

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Target allocation maximum percentage of investments of this type to total plan assets presented on a weighted average basis.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
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Target allocation minimum percentage of investments of this type to total plan assets presented on a weighted average basis.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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