Description of the Business and Summary of Significant Accounting Policies (Intangible Assets) (Details) - USD ($) $ in Thousands		12 Months Ended
	Jun. 29, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)		$ 564,777	$ 526,777
Less accumulated amortization		294,449	269,868
Intangible Assets, Net (Excluding Goodwill), Total		270,328	256,909
Amortization of Intangible Assets		27,780	29,193	$ 28,765
Estimated amortization expense
2019		28,345
2020		26,829
2021		24,656
2022		22,723
2023		20,803
Thereafter		146,972
Total		$ 270,328
Impairment of Long-Lived Tangible and Definite-Lived Intangible Assets
Asset impairment charges				132,839
Weighted average
Finite-Lived Intangible Assets [Line Items]
Useful Life		20 years
Minnesota ironmaking operations
Impairment of Long-Lived Tangible and Definite-Lived Intangible Assets
Asset impairment charges				127,300
Minnesota ironmaking operations | Noncontrolling Interests
Impairment of Long-Lived Tangible and Definite-Lived Intangible Assets
Asset impairment charges				13,100
Customer and scrap generator relationships
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross		$ 435,262	394,062
Useful Life	15 years
Amortization of Intangible Assets		870
Estimated amortization expense
2019		3,600
2020		4,200
2021		3,800
2022		3,500
2023		3,200
Thereafter		$ 22,000
Customer and scrap generator relationships | Minimum
Finite-Lived Intangible Assets [Line Items]
Useful Life		5 years
Customer and scrap generator relationships | Maximum
Finite-Lived Intangible Assets [Line Items]
Useful Life		25 years
Customer and scrap generator relationships | Weighted average
Finite-Lived Intangible Assets [Line Items]
Useful Life		21 years
Trade names
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross		$ 127,350	130,550
Trade names | Minimum
Finite-Lived Intangible Assets [Line Items]
Useful Life		15 years
Trade names | Maximum
Finite-Lived Intangible Assets [Line Items]
Useful Life		25 years
Trade names | Weighted average
Finite-Lived Intangible Assets [Line Items]
Useful Life		19 years
Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross		$ 2,165	2,165
Other Intangible Assets [Member] | Minimum
Finite-Lived Intangible Assets [Line Items]
Useful Life		3 years
Other Intangible Assets [Member] | Maximum
Finite-Lived Intangible Assets [Line Items]
Useful Life		5 years
Other Intangible Assets [Member] | Weighted average
Finite-Lived Intangible Assets [Line Items]
Useful Life		4 years
Other current assets
Impairment of Long-Lived Tangible and Definite-Lived Intangible Assets
Assets held for sale		$ 8,300	8,700
Parent Company [Member]
Impairment of Long-Lived Tangible and Definite-Lived Intangible Assets
Asset impairment charges				12,700
Parent Company [Member] | Minnesota ironmaking operations
Impairment of Long-Lived Tangible and Definite-Lived Intangible Assets
Asset impairment charges				72,900
Guarantors
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Net (Excluding Goodwill), Total		$ 270,328	225,503
Impairment of Long-Lived Tangible and Definite-Lived Intangible Assets
Asset impairment charges				5,500
Combined Non-Guarantors
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Net (Excluding Goodwill), Total			$ 31,406
Impairment of Long-Lived Tangible and Definite-Lived Intangible Assets
Asset impairment charges				$ 116,445