Employee Benefits (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Weighted-average asset allocations of the Company's Defined Benefit Plans by asset category
Equity securities (as a percent)	61.00%	63.00%
Debt securities (as a percent)	36.00%	34.00%
Other (as a percent)	3.00%	3.00%
Total (as a percent)	100.00%	100.00%
Target allocation
Equity securities, minimum (as a percent)	50.00%
Equity securities, maximum (as a percent)	80.00%
Debt securities, minimum (as a percent)	20.00%
Debt securities, maximum (as a percent)	60.00%
Other assets, minimum (as a percent)	0.00%
Other assets, maximum (as a percent)	10.00%
Employee Benefits
Fair value of plan assets	$ 58.9	$ 53.1
Level 1
Employee Benefits
Fair value of plan assets	42.3	31.6
Level 2
Employee Benefits
Fair value of plan assets	16.6	21.5
Common stock
Employee Benefits
Fair value of plan assets	22.7	22.2
Common stock \| Level 1
Employee Benefits
Fair value of plan assets	22.7	22.2
U.S. government, state, and agency
Employee Benefits
Fair value of plan assets	8.1	6.5
U.S. government, state, and agency \| Level 2
Employee Benefits
Fair value of plan assets	8.1	6.5
Corporate debt securities
Employee Benefits
Fair value of plan assets	7.9	6.1
Corporate debt securities \| Level 2
Employee Benefits
Fair value of plan assets	7.9	6.1
Mutual funds
Employee Benefits
Fair value of plan assets	18.6	16.8
Mutual funds \| Level 1
Employee Benefits
Fair value of plan assets	18.0	7.9
Mutual funds \| Level 2
Employee Benefits
Fair value of plan assets	0.6	8.9
Interest and non-interest bearing cash
Employee Benefits
Fair value of plan assets	1.6	1.5
Interest and non-interest bearing cash \| Level 1
Employee Benefits
Fair value of plan assets	$ 1.6	$ 1.5

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The percentage of the fair value of debt securities to the fair value of total plan assets held as of the measurement date.

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The percentage of the fair value of equity securities to the fair value of total plan assets held as of the measurement date.

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