Segment and Geographical Area Information by Operating Segment Table (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Net sales:
Net Sales	$ 332.8	$ 320.6	$ 1,044.4	$ 998.7
Segment operating income (loss):
Operating income (loss)	39.8	29.8	110.7	132.5
Interest expense	(5.3)	(5.5)	(16.4)	(14.7)
Other (expense) income, net	1.5	0.0	3.1	(10.4)
Income before income taxes	36.0	24.3	97.4	107.4
Depreciation and amortization:
Depreciation and amortization	10.2	9.0	29.3	26.7
Capital expenditures:
Capital expenditures	16.4	15.1	56.1	57.4
Assets:
Assets	1,422.7		1,422.7		$ 1,443.5
Fabricated Products
Segment operating income (loss):
Operating income (loss)	53.7	42.1	149.9	172.1
Depreciation and amortization:
Depreciation and amortization	10.1	8.8	28.9	26.2
Capital expenditures:
Capital expenditures	16.3	15.0	55.7	57.1
Assets:
Assets	1,007.9		1,007.9		969.4
All Other
Segment operating income (loss):
Operating income (loss)	(13.9)	(12.3)	(39.2)	(39.6)
Depreciation and amortization:
Depreciation and amortization	0.1	0.2	0.4	0.5
Capital expenditures:
Capital expenditures	0.1	$ 0.1	0.4	$ 0.3
Assets:
Assets	$ 414.8		$ 414.8		$ 474.1