Employee Benefits (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010
Weighted-average asset allocations of the Company's Defined Benefit Plans by asset category
Equity securities (as a percent)	63.00%	68.00%
Debt securities (as a percent)	34.00%	29.00%
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	$ 53.1	$ 53.7
Level 1
Employee Benefits
Fair value of plan assets	31.6	33.6
Level 2
Employee Benefits
Fair value of plan assets	21.5	20.1
Common stock
Employee Benefits
Fair value of plan assets	22.2	23.6
Common stock \| Level 1
Employee Benefits
Fair value of plan assets	22.2	23.6
U.S. government and agency
Employee Benefits
Fair value of plan assets	6.5	6.1
U.S. government and agency \| Level 2
Employee Benefits
Fair value of plan assets	6.5	6.1
State government
Employee Benefits
Fair value of plan assets		0.3
State government \| Level 2
Employee Benefits
Fair value of plan assets		0.3
Corporate debt securities
Employee Benefits
Fair value of plan assets	6.1	6.6
Corporate debt securities \| Level 2
Employee Benefits
Fair value of plan assets	6.1	6.6
Mutual funds
Employee Benefits
Fair value of plan assets	16.8	15.5
Mutual funds \| Level 1
Employee Benefits
Fair value of plan assets	7.9	8.4
Mutual funds \| Level 2
Employee Benefits
Fair value of plan assets	8.9	7.1
Interest and non-interest bearing cash
Employee Benefits
Fair value of plan assets	1.5	1.6
Interest and non-interest bearing cash \| Level 1
Employee Benefits
Fair value of plan assets	$ 1.5	$ 1.6

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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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