Retirement Plans (Narrative) (Details) (USD $)	3 Months Ended	9 Months Ended		12 Months Ended	0 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2013 property	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Oct. 11, 2013 Subsequent Event [Member] property	Oct. 11, 2013 Subsequent Event [Member]	Sep. 30, 2013 Pension Benefits [Member]	Sep. 30, 2013 Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Capitalization of pension and OPEB expense related to engineering and plant construction		$ 14,900,000	$ 11,700,000
Estimated pension and other postretirement benefit expenses, maximum		100,000,000
Pension and other postretirement benefit expenses		22,558,000	24,220,000	81,600,000
Lump sum pension payments		149,000,000
Settlement threshold		125,400,000
Pension settlement costs	(40,309,000)	(40,309,000)					(40,309,000)	(40,309,000)
Net pension plan liability	447,800,000	447,800,000		697,900,000
Funded status of pension plan, percentage	71.00%	71.00%		64.00%
Number of properties contributed	3				1
Contribution of Property	18,200,000	18,216,000			5,200,000
Lease term of contributed property	15 years				15 years
Annual rental payments	1,600,000	1,600,000
Increase in pension obligation	18,200,000
Other liabilities	254,953,000	254,953,000		266,625,000			18,100,000	18,100,000
Other current liabilities	219,234,000	219,234,000		232,836,000			100,000	100,000
Cash contributions to pension plan		38,900,000
Contributions to pension plan		57,100,000				62,300,000
Estimated contributions to pension plan in current fiscal year		0
Plan assets	1,181,100,000	1,181,100,000		1,253,600,000
Decrease in plan assets		72,500,000
Percentage of decrease in pension plan assets		6.00%
Benefit payments		194,700,000
Positive investment returns		$ 65,100,000