Financing Arrangements (Narrative) (Details) - USD ($)	1 Months Ended
	Apr. 30, 2017	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Oct. 31, 2015	Aug. 31, 2015
Line of Credit Facility [Line Items]
Percentage ownership	100.00%
Total debt		$ 591,600,000	$ 541,900,000
Southwest Steel Processing LLC | Arkansas Development Finance Authority
Line of Credit Facility [Line Items]
Maximum borrowing capacity					$ 11,000,000.0
Amount drawn		4,400,000
Machinery and Equipment
Line of Credit Facility [Line Items]
Capital lease obligations		$ 19,300,000
Maximum
Line of Credit Facility [Line Items]
Capital lease obligations						$ 50,000,000.0
Revolving credit
Line of Credit Facility [Line Items]
Stated interest rate		3.3331%
Total debt		$ 172,000,000	124,700,000
Foreign Line of Credit
Line of Credit Facility [Line Items]
Stated interest rate		3.25%
Total debt		$ 27,700,000	$ 27,000,000
Line of Credit | Foreign Line of Credit | Banco Bolbao Vizcaya Argentaria, S.A.
Line of Credit Facility [Line Items]
Maximum borrowing capacity				$ 27,700,000.0
Seventh Amendment Credit Agreement | Revolving credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 350,000,000.0
Increase in additional borrowing capacity	100,000,000.0
Financing Agreement | Line of Credit | Revolving credit | Banco Bolbao Vizcaya Argentaria, S.A.
Line of Credit Facility [Line Items]
Maximum borrowing capacity				$ 12,400,000.0
Amount drawn		$ 0
Park-Ohio Industries, Inc. | Senior Notes Due 2027 | Senior Notes
Line of Credit Facility [Line Items]
Aggregate principal amount	$ 350,000,000.0
Stated interest rate	6.625%