Segment Information - Results (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Segment Reporting Information
Net sales	$ 2,575,100	$ 2,817,435
Operating income (loss)	273,686	291,842
Income (loss) before income taxes	248,256	267,063
Depreciation and amortization	80,259	80,174
Capital expenditures	217,535	54,436
Assets	8,344,923		$ 8,275,765
U.S.
Segment Reporting Information
Net sales		2,671,893
Non-U.S.
Segment Reporting Information
Net sales		145,542
Operating Segment | Other segments
Segment Reporting Information
Net sales	(411,922)
Operating Segment | U.S.
Segment Reporting Information
Net sales	2,436,695
Operating Segment | Non-U.S.
Segment Reporting Information
Net sales	138,405
Operating Segment | Steel Operations
Segment Reporting Information
Net sales	2,016,152	2,200,165
Operating income (loss)	288,394	309,078
Income (loss) before income taxes	273,555	293,019
Depreciation and amortization	62,427	62,512
Capital expenditures	193,273	43,676
Assets	5,458,553
Operating Segment | Steel Operations | Other segments
Segment Reporting Information
Net sales	74,446	75,595
Operating Segment | Steel Operations | U.S.
Segment Reporting Information
Net sales	1,860,585	2,044,491
Operating Segment | Steel Operations | Non-U.S.
Segment Reporting Information
Net sales	81,121	80,079
Operating Segment | Metals Recycling Operations
Segment Reporting Information
Net sales	628,739	737,045
Operating income (loss)	5,528	16,962
Income (loss) before income taxes	4,305	15,505
Depreciation and amortization	11,972	11,439
Capital expenditures	18,223	6,642
Assets	918,403
Operating Segment | Metals Recycling Operations | Other segments
Segment Reporting Information
Net sales	336,882	385,908
Operating Segment | Metals Recycling Operations | U.S.
Segment Reporting Information
Net sales	234,833	285,725
Operating Segment | Metals Recycling Operations | Non-U.S.
Segment Reporting Information
Net sales	57,024	65,412
Operating Segment | Steel Fabrication Operations
Segment Reporting Information
Net sales	221,441	228,669
Operating income (loss)	29,163	20,623
Income (loss) before income taxes	27,918	19,351
Depreciation and amortization	2,748	2,967
Capital expenditures	4,089	1,993
Assets	405,860
Operating Segment | Steel Fabrication Operations | Other segments
Segment Reporting Information
Net sales	506	189
Operating Segment | Steel Fabrication Operations | U.S.
Segment Reporting Information
Net sales	220,935	228,429
Operating Segment | Steel Fabrication Operations | Non-U.S.
Segment Reporting Information
Net sales		51
Operating Segment | Other
Segment Reporting Information
Net sales	120,690	113,496
Operating income (loss)	(46,355)	(56,920)
Income (loss) before income taxes	(54,240)	(62,696)
Depreciation and amortization	3,112	3,256
Capital expenditures	1,950	2,125
Assets	1,619,924
Operating Segment | Other | Other segments
Segment Reporting Information
Net sales	88	248
Operating Segment | Other | U.S.
Segment Reporting Information
Net sales	120,342	113,248
Operating Segment | Other | Non-U.S.
Segment Reporting Information
Net sales	260
Eliminations
Segment Reporting Information
Net sales	(411,922)	(461,940)
Operating income (loss)	(3,044)	2,099
Income (loss) before income taxes	(3,282)	1,884
Assets	$ (57,817)
Eliminations | Other segments
Segment Reporting Information
Net sales		$ (461,940)