Financing Arrangements (Narrative) (Details) - USD ($)		12 Months Ended
	Apr. 17, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 21, 2016	Oct. 21, 2015	Aug. 13, 2015
Line of Credit Facility [Line Items]
Ownership percentage of domestic subsidiaries		100.00%
Repayments of Long-term Debt		$ 31,300,000	$ 4,500,000	$ 3,600,000
Loss on extinguishment of debt		(11,000,000)	0	0
Premium on early extinguishment of debt		8,000,000	0	$ 0
Capital lease agreement							$ 50,000,000
Foreign subsidiaries borrowings amount		40,200,000	42,400,000
Foreign subsidiaries bank guarantee amount		$ 15,100,000	$ 15,100,000
Weighted average interest rate		6.11%	6.10%
Machinery and Equipment
Line of Credit Facility [Line Items]
Capital lease agreement		$ 20,300,000
Arkansas Development Finance Authority | Southwest Steel Processing LLC
Line of Credit Facility [Line Items]
Maximum borrowing capacity						$ 11,000,000.0
Amount outstanding		5,300,000
Senior Notes Due 2021 And Seventh Amendment To Credit Facility
Line of Credit Facility [Line Items]
Loss on extinguishment of debt	$ (11,000,000)
Premium on early extinguishment of debt	8,000,000
Write off of deferred debt issuance cost	2,500,000
Payments of financing costs	500,000
Term Loan
Line of Credit Facility [Line Items]
Repayments of Long-term Debt	250,000,000
U.S. Line of Credit | Seventh Amendment Credit Agreement
Line of Credit Facility [Line Items]
Amount outstanding		$ 112,700,000
Revolving credit facility
Line of Credit Facility [Line Items]
Senior notes, interest rate		3.299%
Revolving credit facility | Seventh Amendment Credit Agreement
Line of Credit Facility [Line Items]
Maximum borrowing capacity	350,000,000.0
Accordion feature, increase limit	$ 100,000,000.0
Remaining borrowing capacity		$ 194,200,000
Revolving credit facility, European sub-limit | Seventh Amendment Credit Agreement
Line of Credit Facility [Line Items]
Amount outstanding		12,000,000
Current borrowing capacity		25,000,000
Revolving credit facility, Canadian sub-limit | Seventh Amendment Credit Agreement
Line of Credit Facility [Line Items]
Current borrowing capacity		$ 35,000,000
Foreign Line of Credit
Line of Credit Facility [Line Items]
Senior notes, interest rate		3.25%
Senior Notes
Line of Credit Facility [Line Items]
Senior notes, interest rate	8.125%
Senior Notes | Senior Notes Due 2027
Line of Credit Facility [Line Items]
Aggregate principal amount	$ 350,000,000.0
Senior Notes | Senior Notes 6.625% Due 2027
Line of Credit Facility [Line Items]
Senior notes, interest rate	6.625%	6.625%
Banco Bolbao Vizcaya Argentaria, S.A. | Line of Credit | Revolving credit facility | Financing Agreement
Line of Credit Facility [Line Items]
Maximum borrowing capacity					$ 12,100,000.0
Amount outstanding		$ 0
Banco Bolbao Vizcaya Argentaria, S.A. | Line of Credit | Foreign Line of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity					$ 27,000,000