Employee Incentive Plans Employee Incentive Plans, Compensation expense under LTI programs (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cumulative-effect adjustment	[1]			$ 0.7
Allocated Share-based Compensation Expense		$ 2.6	$ 2.1
Restricted Stock And Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		1.1	1.1
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		0.3	0.4
Market-based shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		1.1	0.6
Cost Performance-Based Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		0.1	0.0
Fabricated Products
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		0.8	0.7
All Other
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		$ 1.8	$ 1.4
Minimum | Market-based shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		0.00%
Minimum | Cost Performance-Based Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		0.00%
Maximum | Market-based shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		200.00%
Maximum | Cost Performance-Based Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		200.00%
Additional Paid in Capital
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cumulative-effect adjustment	[1]			0.8
Accounting Standards Update 2016-09 | New Accounting Pronouncement, Early Adoption, Effect
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cumulative-effect adjustment	[1]			0.7
Accounting Standards Update 2016-09 | New Accounting Pronouncement, Early Adoption, Effect | Additional Paid in Capital
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cumulative-effect adjustment	[1]			$ 0.8

[1] See Note 4 and Note 6 for discussion of our adoption of ASU 2016-09 (as defined in Note 1).