Employee Benefit Plans, Target and Actual Asset Allocation (Details) (Defined Benefit Pension Plan and Benefit Equalization Plan [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Pension Plan Assets [Abstract]
Target asset allocation (in hundredths)	100.00%
Actual asset allocation (in hundredths)	100.00%	100.00%
Decrease in cash position (in hundredths)	(35.20%)
Investments in hedge funds which do not have readily determinable fair values	$ 44.3	$ 31.1
Expected contributions to the defined benefit pension plan in 2013	1.7
Cash and Cash Equivalents [Member]
Pension Plan Assets [Abstract]
Target asset allocation (in hundredths)	5.00%
Actual asset allocation (in hundredths)	6.60%	41.80%
Domestic Equity Securities [Member]
Pension Plan Assets [Abstract]
Target asset allocation (in hundredths)	70.00%
Actual asset allocation (in hundredths)	67.50%	49.50%
International Equity Securities [Member]
Pension Plan Assets [Abstract]
Target asset allocation (in hundredths)	20.00%
Actual asset allocation (in hundredths)	20.80%	8.70%
Fixed Income Securities [Member]
Pension Plan Assets [Abstract]
Target asset allocation (in hundredths)	5.00%
Actual asset allocation (in hundredths)	5.10%	0.00%
Fixed Income and Equity Securities [Member]
Pension Plan Assets [Abstract]
Purchase of assets	5.7
Global Equity Partnership Fund [Member]
Pension Plan Assets [Abstract]
Purchase of assets	5.0
Hedge Funds [Member]
Pension Plan Assets [Abstract]
Purchase of assets	$ 11.5