Segment and Geographical Area Information by Operating Segment Table (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Net sales:
Net Sales	$ 388.0	$ 355.3
Segment operating income (loss):
Operating Income (Loss)	37.1	59.3
Interest expense	(5.6)	(5.6)
Other income, net	0.1	0.8
Income before income taxes	31.6	54.5
Depreciation and amortization:
Depreciation and amortization	10.5	9.6
Capital expenditures:
Capital expenditures	19.7	14.8
Assets:
Assets	1,405.4		$ 1,396.8	$ 1,385.2
Fabricated Products
Segment operating income (loss):
Operating Income (Loss)	49.5	70.6
Depreciation and amortization:
Depreciation and amortization	10.3	9.4
Capital expenditures:
Capital expenditures	19.6	14.6
Assets:
Assets	1,086.3			1,046.8
All Other
Segment operating income (loss):
Operating Income (Loss)	(12.4)	(11.3)
Depreciation and amortization:
Depreciation and amortization	0.2	0.2
Capital expenditures:
Capital expenditures	0.1	$ 0.2
Assets:
Assets	$ 319.1			$ 338.4