Borrowings (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended			0 Months Ended			1 Months Ended	12 Months Ended								0 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Nov. 20, 2012 3.75% senior notes due 2022	Dec. 31, 2012 3.75% senior notes due 2022	Dec. 31, 2012 3.75% senior notes due 2022 Significant Observable Inputs (Level 2)	Dec. 31, 2010 5.125% senior notes due 2020	Dec. 31, 2012 5.125% senior notes due 2020	Dec. 31, 2011 5.125% senior notes due 2020	Dec. 09, 2010 5.125% senior notes due 2020	Dec. 31, 2012 5.125% senior notes due 2020 Subsidiaries	Dec. 31, 2012 5.125% senior notes due 2020 Significant Observable Inputs (Level 2)	Dec. 31, 2012 6.125% senior notes due 2016	Dec. 31, 2011 6.125% senior notes due 2016	Dec. 31, 2012 6.125% senior notes due 2016 Significant Observable Inputs (Level 2)	Jan. 10, 2011 8.75% Hawk senior notes due 2014	Dec. 31, 2012 8.75% Hawk senior notes due 2014	Dec. 02, 2010 8.75% Hawk senior notes due 2014	Dec. 31, 2012 Revolving credit facility	Dec. 31, 2011 Revolving credit facility	Oct. 20, 2011 Revolving credit facility	Dec. 31, 2012 Industrial development and revenue bonds through 2018	Dec. 31, 2011 Industrial development and revenue bonds through 2018	Dec. 31, 2012 Other, including capital lease obligations	Dec. 31, 2011 Other, including capital lease obligations	Dec. 31, 2012 Uncommitted line of credit	Dec. 31, 2011 Uncommitted line of credit
Borrowings
Total long-term debt	$ 752.5	$ 762.4			$ 348.9			$ 249.1	$ 249.0				$ 149.6	$ 149.5						$ 348.0		$ 4.5	$ 5.5	$ 0.4	$ 10.4
Less current portion		(158.1)
Total long-term debt, net of current portion	752.5	604.3
Interest rate (as a percent)				3.75%	3.75%			5.125%	5.125%	5.125%			6.125%	6.125%			8.75%	8.75%
Unamortized discount				(1.1)	(1.1)			(0.9)	(1.0)	(1.1)			(0.4)	(0.5)
Par value of senior notes				350.0	350.0			250.0		250.0			150.0			57.1
Proceeds from issuance of debt				348.9			248.9
Issuance costs including underwriter's, credit rating agencies' and attorneys' fees and other costs, which are included in other long-term assets	2.9	1.8	1.9	2.9			1.9
Percentage of principal amount at which the entity may redeem some or all of the notes prior to September 15, 2020								100.00%
Long-term debt redemption price, description of variable discount rate								Treasury Rate
Long-term debt redemption price, basis spread on variable discount rate (as a percent)								0.35%
Percentage of principal amount at which the entity may redeem some or all of the notes after September 15, 2020								100.00%
Percentage of the principal amount at which the notes are redeemable due to a change of control								101.00%
Subsidiaries indebtedness											4.9
Fair value of notes						355.4						275.3			171.5			59.0
Redemption amount of senior notes																59.1
Contractual redemption premium of senior notes																1.9
Accrued and unpaid interest of senior notes																0.1
Maximum borrowing capacity																					600.0					45.0	35.0
Remaining borrowing capacity																			600.0
Short-term debt, including current maturities		158.1
Average interest rate (as a percent)																			1.30%	0.84%		1.22%	1.12%			1.58%	1.50%
Outstanding issued letters of credit	31.8
Cash payments for interest	25.7	23.0	9.3
Long-term debt, by maturity
2016	150.0
2018	4.5
2020	250
2022	350.0
Interest income	$ 0.5	$ 0.5	$ 0.3