Segment and Geographical Area Information by Operating Segment Table (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Net sales:
Net Sales	$ 356.3	$ 334.9	$ 711.6	$ 678.1
Segment operating income (loss):
Operating income (loss)	11.4	57.9	70.9	102.7
Interest expense	(5.5)	(5.5)	(11.1)	(9.2)
Other (expense) income, net	1.0	(10.7)	1.6	(10.4)
Income before income taxes	6.9	41.7	61.4	83.1
Depreciation and amortization:
Depreciation and amortization	9.5	9.0	19.1	17.7
Capital expenditures:
Capital expenditures	24.9	16.4	39.7	42.3
Assets:
Assets	1,386.7		1,386.7		$ 1,443.5
Fabricated Products
Segment operating income (loss):
Operating income (loss)	25.6	72.1	96.2	130.0
Depreciation and amortization:
Depreciation and amortization	9.4	8.8	18.8	17.4
Capital expenditures:
Capital expenditures	24.8	16.3	39.4	42.1
Assets:
Assets	991.5		991.5		969.4
All Other
Segment operating income (loss):
Operating income (loss)	(14.2)	(14.2)	(25.3)	(27.3)
Depreciation and amortization:
Depreciation and amortization	0.1	0.2	0.3	0.3
Capital expenditures:
Capital expenditures	0.1	$ 0.1	0.3	$ 0.2
Assets:
Assets	$ 395.2		$ 395.2		$ 474.1