Segment and Geographical Area Information Segment and Geographical Area Information, Information by Geographical Area (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012		Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Revenues from External Customers, Income Taxes Paid, and Long-Lived Assets
Net sales to unaffiliated customers	$ 311.3		$ 319.9	$ 328.9	$ 337.4	$ 314.0		$ 335.5	$ 345.2	$ 365.4	$ 1,297.5		$ 1,360.1		$ 1,301.3
Income taxes paid											2.1		1.8		3.5
Long-lived assets	429.3	[1]				384.3	[1]				429.3	[1]	384.3	[1]	367.8	[1]
Fabricated Products
Revenues from External Customers, Income Taxes Paid, and Long-Lived Assets
Net sales to unaffiliated customers											1,297.5		1,360.1		1,301.3
Long-lived assets	424.8	[1]				380.0	[1]				424.8	[1]	380.0	[1]	363.3	[1]
Fabricated Products | United States
Revenues from External Customers, Income Taxes Paid, and Long-Lived Assets
Net sales to unaffiliated customers											1,204.7		1,256.5		1,195.1
Income taxes paid											1.2		0.5		1.7
Long-lived assets	409.5	[1]				367.5	[1]				409.5	[1]	367.5	[1]	351.4	[1]
Fabricated Products | Canada
Revenues from External Customers, Income Taxes Paid, and Long-Lived Assets
Net sales to unaffiliated customers											92.8		103.6		106.2
Income taxes paid											0.9		1.3		1.8
Long-lived assets	15.3	[1]				12.5	[1]				15.3	[1]	12.5	[1]	11.9	[1]
All Other
Revenues from External Customers, Income Taxes Paid, and Long-Lived Assets
Long-lived assets	4.5	[1]				4.3	[1]				4.5	[1]	4.3	[1]	4.5	[1]
All Other | United States
Revenues from External Customers, Income Taxes Paid, and Long-Lived Assets
Long-lived assets	$ 4.5	[1]				$ 4.3	[1]				$ 4.5	[1]	$ 4.3	[1]	$ 4.5	[1]

[1] Long-lived assets represent Property, plant and equipment, net.