Financing Arrangements (Narrative) (Details) - USD ($)	Apr. 22, 2016	Mar. 31, 2017	Dec. 31, 2016	Dec. 21, 2016	Oct. 21, 2015	Aug. 13, 2015	Oct. 23, 2014
Line of Credit Facility [Line Items]
Carrying amount		$ 486,700,000	$ 475,000,000
Machinery and Equipment
Line of Credit Facility [Line Items]
Capital lease obligations		19,900,000
Southwest Steel Processing LLC | Arkansas Development Finance Authority
Line of Credit Facility [Line Items]
Maximum borrowing capacity					$ 11,000,000.0
Amount drawn		6,100,000
Maximum
Line of Credit Facility [Line Items]
Capital lease obligations						$ 50,000,000
Foreign Line of Credit
Line of Credit Facility [Line Items]
Carrying amount		$ 26,700,000	26,400,000
Stated interest rate		3.25%
Revolving credit
Line of Credit Facility [Line Items]
Carrying amount		$ 145,800,000	132,800,000
Stated interest rate		4.098%
Term Loan
Line of Credit Facility [Line Items]
Carrying amount		$ 22,300,000	23,400,000
Stated interest rate		3.00%
Amendment No. 1 to the Amended Credit Agreement | Revolving credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 300,000,000.0
Inventory advance rate percentage to be reduced to	50.00%
Term over which inventory advance rate percentage reduces	36 months
Amount drawn	$ 35,000,000
Term over which basis spread on variable interest rate reduces	36 months
Amendment No. 1 to the Amended Credit Agreement | Revolving credit | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable interest rate - plus (minus)	(3.50%)
Amendment No. 1 to the Amended Credit Agreement | Revolving Credit Facility, Canadian Sub-Limit
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 35,000,000.0
Amendment No. 1 to the Amended Credit Agreement | Revolving Credit Facility, European Sub-Limit
Line of Credit Facility [Line Items]
Maximum borrowing capacity	25,000,000.0
Amendment No. 1 to the Amended Credit Agreement | Term Loan
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 35,000,000.0
The Amended Credit Agreement | Revolving credit
Line of Credit Facility [Line Items]
Inventory advance rate percentage	65.00%						50.00%
Term of debt instrument	7 years
The Amended Credit Agreement | Revolving credit | LIBOR | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable interest rate - plus (minus)	(1.50%)
The Amended Credit Agreement | Revolving credit | LIBOR | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable interest rate - plus (minus)	(2.50%)
The Amended Credit Agreement | Revolving credit | Prime lending rate | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable interest rate - plus (minus)	0.25%
The Amended Credit Agreement | Revolving credit | Prime lending rate | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable interest rate - plus (minus)	1.25%
The Amended Credit Agreement | Revolving Credit Facility, Canadian Sub-Limit | Canadian deposit offered rate | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable interest rate - plus (minus)	(1.50%)
The Amended Credit Agreement | Revolving Credit Facility, Canadian Sub-Limit | Canadian deposit offered rate | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable interest rate - plus (minus)	(2.50%)
The Amended Credit Agreement | Revolving Credit Facility, Canadian Sub-Limit | Canadian prime lending rate | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable interest rate - plus (minus)	0.00%
The Amended Credit Agreement | Revolving Credit Facility, Canadian Sub-Limit | Canadian prime lending rate | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable interest rate - plus (minus)	(1.00%)
The Amended Credit Agreement | Revolving Credit Facility, Canadian Sub-Limit | US base rate | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable interest rate - plus (minus)	0.00%
The Amended Credit Agreement | Revolving Credit Facility, Canadian Sub-Limit | US base rate | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable interest rate - plus (minus)	(1.00%)
The Amended Credit Agreement | Term Loan | LIBOR | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable interest rate - plus (minus)	(2.00%)
The Amended Credit Agreement | Term Loan | LIBOR | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable interest rate - plus (minus)	(3.00%)
The Amended Credit Agreement | Term Loan | Prime lending rate | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable interest rate - plus (minus)	0.75%
The Amended Credit Agreement | Term Loan | Prime lending rate | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable interest rate - plus (minus)	(0.25%)
Line of Credit | Banco Bolbao Vizcaya Argentaria, S.A. | Foreign Line of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity				$ 36,900,000.0
Line of Credit | Banco Bolbao Vizcaya Argentaria, S.A. | Financing Agreement | Revolving credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity				10,500,000.0
Amount drawn			0
Senior Notes
Line of Credit Facility [Line Items]
Carrying amount		$ 250,000,000	$ 250,000,000
Stated interest rate		8.125%
GH Electrotermia S.A. | Line of Credit | Banco Bolbao Vizcaya Argentaria, S.A. | Financing Agreement | Foreign Line of Credit
Line of Credit Facility [Line Items]
Amount drawn				$ 26,400,000