Segment Information - Results (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Segment Reporting Information
Net sales	$ 2,817,435	$ 2,603,875
Operating income (loss)	291,842	323,397
Income (loss) before income taxes	267,063	295,964
Depreciation and amortization	80,174	76,135
Capital expenditures	54,436	50,606
Assets	7,857,233		$ 7,703,563
U.S.
Segment Reporting Information
Net sales	2,671,893	2,456,083
Non-U.S.
Segment Reporting Information
Net sales	145,542	147,792
Operating Segment \| Steel Operations
Segment Reporting Information
Net sales	2,200,165	1,981,774
Operating income (loss)	309,078	334,562
Income (loss) before income taxes	293,019	315,805
Depreciation and amortization	62,512	59,141
Capital expenditures	43,676	38,402
Assets	5,378,536
Operating Segment \| Steel Operations \| Other segments
Segment Reporting Information
Net sales	75,595	59,985
Operating Segment \| Steel Operations \| U.S.
Segment Reporting Information
Net sales	2,044,491	1,832,303
Operating Segment \| Steel Operations \| Non-U.S.
Segment Reporting Information
Net sales	80,079	89,486
Operating Segment \| Metals Recycling Operations
Segment Reporting Information
Net sales	737,045	752,766
Operating income (loss)	16,962	24,715
Income (loss) before income taxes	15,505	23,005
Depreciation and amortization	11,439	11,558
Capital expenditures	6,642	6,946
Assets	982,844
Operating Segment \| Metals Recycling Operations \| Other segments
Segment Reporting Information
Net sales	385,908	364,644
Operating Segment \| Metals Recycling Operations \| U.S.
Segment Reporting Information
Net sales	285,725	329,872
Operating Segment \| Metals Recycling Operations \| Non-U.S.
Segment Reporting Information
Net sales	65,412	58,250
Operating Segment \| Steel Fabrication Operations
Segment Reporting Information
Net sales	228,669	201,703
Operating income (loss)	20,623	19,791
Income (loss) before income taxes	19,351	18,457
Depreciation and amortization	2,967	2,898
Capital expenditures	1,993	2,077
Assets	407,576
Operating Segment \| Steel Fabrication Operations \| Other segments
Segment Reporting Information
Net sales	189	210
Operating Segment \| Steel Fabrication Operations \| U.S.
Segment Reporting Information
Net sales	228,429	201,437
Operating Segment \| Steel Fabrication Operations \| Non-U.S.
Segment Reporting Information
Net sales	51	56
Operating Segment \| Other
Segment Reporting Information
Net sales	113,496	92,618
Operating income (loss)	(56,920)	(55,406)
Income (loss) before income taxes	(62,696)	(61,033)
Depreciation and amortization	3,256	2,538
Capital expenditures	2,125	3,181
Assets	1,170,832
Operating Segment \| Other \| Other segments
Segment Reporting Information
Net sales	248	147
Operating Segment \| Other \| U.S.
Segment Reporting Information
Net sales	113,248	92,471
Eliminations
Segment Reporting Information
Net sales	(461,940)	(424,986)
Operating income (loss)	2,099	(265)
Income (loss) before income taxes	1,884	(270)
Assets	(82,555)
Eliminations \| Other segments
Segment Reporting Information
Net sales	$ (461,940)	$ (424,986)

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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