Segment Information - Results (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Segment Reporting Information
Net sales	$ 2,101,310	$ 1,950,923	$ 5,866,513	$ 6,003,365
Operating income (loss)	283,855	131,029	671,942	308,359
Income (loss) before income taxes	243,305	93,706	561,313	175,806
Depreciation and amortization	74,190	74,211	222,970	221,306
Capital expenditures	59,774	30,286	123,168	86,458
Assets	6,787,562	6,842,541	6,787,562	6,842,541	$ 6,202,082
U.S.
Segment Reporting Information
Net sales	2,000,867	1,831,665	5,576,165	5,643,000
Non-U.S.
Segment Reporting Information
Net sales	100,443	119,258	290,348	360,365
Steel Operations
Segment Reporting Information
Net sales	1,627,886	1,407,533	4,419,572	4,271,091
Operating income (loss)	307,553	124,712	712,939	338,690
Income (loss) before income taxes	285,131	102,566	645,189	269,187
Depreciation and amortization	53,456	52,404	159,614	154,616
Capital expenditures	49,200	21,975	103,202	52,324
Assets	4,147,447	4,096,188	4,147,447	4,096,188
Steel Operations | Other segments
Segment Reporting Information
Net sales	70,384	56,146	178,190	158,609
Steel Operations | U.S.
Segment Reporting Information
Net sales	1,502,726	1,285,459	4,068,688	3,902,162
Steel Operations | Non-U.S.
Segment Reporting Information
Net sales	54,776	65,928	172,694	210,320
Metals Recycling Operations
Segment Reporting Information
Net sales	565,263	616,460	1,643,172	1,913,921
Operating income (loss)	6,154	(3,555)	20,014	229
Income (loss) before income taxes	2,437	(6,967)	10,300	(12,780)
Depreciation and amortization	13,836	15,913	42,666	50,207
Capital expenditures	9,506	6,286	17,068	17,332
Assets	1,034,637	1,588,821	1,034,637	1,588,821
Metals Recycling Operations | Other segments
Segment Reporting Information
Net sales	259,171	270,888	756,613	751,542
Metals Recycling Operations | U.S.
Segment Reporting Information
Net sales	260,518	294,357	769,260	1,014,753
Metals Recycling Operations | Non-U.S.
Segment Reporting Information
Net sales	45,574	51,215	117,299	147,626
Steel Fabrication Operations
Segment Reporting Information
Net sales	178,640	174,956	530,441	490,509
Operating income (loss)	17,744	36,733	73,230	85,754
Income (loss) before income taxes	15,645	35,108	67,175	80,581
Depreciation and amortization	2,848	2,300	8,431	6,688
Capital expenditures	747	935	1,918	2,506
Assets	353,560	372,673	353,560	372,673
Steel Fabrication Operations | Other segments
Segment Reporting Information
Net sales	1,211	2	2,415	18
Steel Fabrication Operations | U.S.
Segment Reporting Information
Net sales	177,341	173,047	527,859	488,584
Steel Fabrication Operations | Non-U.S.
Segment Reporting Information
Net sales	88	1,907	167	1,907
Other
Segment Reporting Information
Net sales	61,395	83,219	214,149	267,127
Operating income (loss)	(47,687)	(28,401)	(125,186)	(117,273)
Income (loss) before income taxes	(59,999)	(38,541)	(152,296)	(162,141)
Depreciation and amortization	4,101	3,645	12,413	9,948
Capital expenditures	321	1,090	980	14,296
Assets	1,374,469	898,772	1,374,469	898,772
Other | Other segments
Segment Reporting Information
Net sales	1,108	4,209	3,603	29,114
Other | U.S.
Segment Reporting Information
Net sales	60,282	78,802	210,358	237,501
Other | Non-U.S.
Segment Reporting Information
Net sales	5	208	188	512
Eliminations
Segment Reporting Information
Net sales	(331,874)	(331,245)	(940,821)	(939,283)
Operating income (loss)	91	1,540	(9,055)	959
Income (loss) before income taxes	91	1,540	(9,055)	959
Depreciation and amortization	(51)	(51)	(154)	(153)
Assets	(122,551)	(113,913)	(122,551)	(113,913)
Eliminations | Other segments
Segment Reporting Information
Net sales	$ (331,874)	$ (331,245)	$ (940,821)	$ (939,283)