Employee Benefits (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Employee Benefits
Weighted-average asset allocations (as a percent)	100.00%	100.00%
Target allocation
Fair value of plan assets	$ 72.4	$ 70.2
Level 1
Target allocation
Fair value of plan assets	52.6	55.1
Level 2
Target allocation
Fair value of plan assets	19.8	15.1
U.S. government, state, and agency
Target allocation
Fair value of plan assets	7.1	6.3
U.S. government, state, and agency \| Level 2
Target allocation
Fair value of plan assets	7.1	6.3
Corporate debt securities
Target allocation
Fair value of plan assets	10.0	8.4
Corporate debt securities \| Level 2
Target allocation
Fair value of plan assets	10.0	8.4
Mutual funds
Target allocation
Fair value of plan assets	25.3	28.3
Mutual funds \| Level 1
Target allocation
Fair value of plan assets	22.6	27.9
Mutual funds \| Level 2
Target allocation
Fair value of plan assets	2.7	0.4
Interest and non-interest bearing cash
Target allocation
Fair value of plan assets	3.4	1.6
Interest and non-interest bearing cash \| Level 1
Target allocation
Fair value of plan assets	3.4	1.6
Equity securities
Employee Benefits
Weighted-average asset allocations (as a percent)	58.00%	61.00%
Target allocation
Target allocation, minimum (as a percent)	50.00%
Target allocation, maximum (as a percent)	80.00%
Fair value of plan assets	26.6	25.6
Equity securities \| Level 1
Target allocation
Fair value of plan assets	$ 26.6	$ 25.6
Debt securities
Employee Benefits
Weighted-average asset allocations (as a percent)	37.00%	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)	5.00%	2.00%
Target allocation
Target allocation, minimum (as a percent)	0.00%
Target allocation, maximum (as a percent)	10.00%

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- Definition

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

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

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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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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.

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