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Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014 segment	Dec. 31, 2013	Dec. 31, 2012
Segment Information
Number of reporting segments									3us-gaap_NumberOfReportableSegments
Segment Reporting Information
Total net sales	$ 2,517,093us-gaap_SalesRevenueNet	$ 2,339,016us-gaap_SalesRevenueNet	$ 2,069,761us-gaap_SalesRevenueNet	$ 1,830,082us-gaap_SalesRevenueNet	$ 1,864,150us-gaap_SalesRevenueNet	$ 1,911,738us-gaap_SalesRevenueNet	$ 1,801,340us-gaap_SalesRevenueNet	$ 1,795,696us-gaap_SalesRevenueNet	$ 8,755,952us-gaap_SalesRevenueNet	$ 7,372,924us-gaap_SalesRevenueNet	$ 7,290,234us-gaap_SalesRevenueNet
Operating income (loss)	(81,160)us-gaap_OperatingIncomeLoss	188,643us-gaap_OperatingIncomeLoss	131,905us-gaap_OperatingIncomeLoss	80,932us-gaap_OperatingIncomeLoss	107,822us-gaap_OperatingIncomeLoss	113,273us-gaap_OperatingIncomeLoss	69,198us-gaap_OperatingIncomeLoss	96,232us-gaap_OperatingIncomeLoss	320,320us-gaap_OperatingIncomeLoss	386,525us-gaap_OperatingIncomeLoss	391,165us-gaap_OperatingIncomeLoss
Income (loss) before income taxes									164,803	262,830	204,066
Depreciation and amortization									263,325	230,928	225,216
Capital expenditures									111,785	186,843	223,525
Assets	7,311,027us-gaap_Assets				5,933,006us-gaap_Assets				7,311,027us-gaap_Assets	5,933,006us-gaap_Assets	5,815,416us-gaap_Assets
Liabilities	4,389,160us-gaap_Liabilities				3,320,637us-gaap_Liabilities				4,389,160us-gaap_Liabilities	3,320,637us-gaap_Liabilities	3,338,760us-gaap_Liabilities
Impairment charges	260,000us-gaap_AssetImpairmentCharges								260,000us-gaap_AssetImpairmentCharges	308us-gaap_AssetImpairmentCharges	8,250us-gaap_AssetImpairmentCharges
U.S.
Segment Reporting Information
Total net sales									8,272,958	6,955,726	6,851,365
Non-U.S.
Segment Reporting Information
Total net sales									482,994	417,198	438,869
Steel Operations
Segment Reporting Information
Capital expenditures									61,426	121,835	55,786
Metals Recycling/Ferrous Resources
Segment Reporting Information
Capital expenditures									46,374	60,678	159,768
Impairment charges	46,500
Steel Fabrication Operations
Segment Reporting Information
Capital expenditures									3,027	2,166	5,735
Other.
Segment Reporting Information
Capital expenditures									958	2,164	2,236
Operating Segment
Segment Reporting Information
Total net sales									8,755,952	7,372,924	7,290,234
Operating Segment \| Steel Operations
Segment Reporting Information
Total net sales									5,821,578	4,685,170	4,701,108
Operating income (loss)									671,607	504,384	495,640
Income (loss) before income taxes									602,651	449,405	425,509
Depreciation and amortization									139,761	106,603	104,222
Assets	4,406,402				2,642,866				4,406,402	2,642,866	2,485,235
Liabilities	768,047				563,924				768,047	563,924	525,351
Operating Segment \| Steel Operations \| Other segments
Segment Reporting Information
Total net sales									279,835	223,713	194,320
Operating Segment \| Steel Operations \| U.S.
Segment Reporting Information
Total net sales									5,300,762	4,256,077	4,294,437
Operating Segment \| Steel Operations \| Non-U.S.
Segment Reporting Information
Total net sales									240,981	205,380	212,351
Operating Segment \| Metals Recycling/Ferrous Resources
Segment Reporting Information
Total net sales									3,769,241	3,558,719	3,611,796
Operating income (loss)									(308,730)	(52,468)	(36,508)
Income (loss) before income taxes									(335,974)	(84,826)	(70,433)
Depreciation and amortization									108,743	109,847	103,993
Assets	2,169,902				2,549,626				2,169,902	2,549,626	2,568,233
Liabilities	574,850				588,232				574,850	588,232	484,017
Impairment charges									260,000
Operating Segment \| Metals Recycling/Ferrous Resources \| Other segments
Segment Reporting Information
Total net sales									1,282,272	1,173,878	1,269,198
Operating Segment \| Metals Recycling/Ferrous Resources \| U.S.
Segment Reporting Information
Total net sales									2,246,069	2,173,863	2,116,537
Operating Segment \| Metals Recycling/Ferrous Resources \| Non-U.S.
Segment Reporting Information
Total net sales									240,900	210,978	226,061
Operating Segment \| Steel Fabrication Operations
Segment Reporting Information
Total net sales									631,808	439,655	371,406
Operating income (loss)									51,894	7,003	2,114
Income (loss) before income taxes									45,376	827	(4,580)
Depreciation and amortization									9,712	8,736	8,025
Assets	301,316				270,215				301,316	270,215	242,747
Liabilities	42,234				22,704				42,234	22,704	15,983
Operating Segment \| Steel Fabrication Operations \| Other segments
Segment Reporting Information
Total net sales									58	1,401	322
Operating Segment \| Steel Fabrication Operations \| U.S.
Segment Reporting Information
Total net sales									631,750	438,254	371,084
Operating Segment \| Other.
Segment Reporting Information
Total net sales									122,986	115,326	87,462
Operating income (loss)									(98,879)	(71,446)	(66,829)
Income (loss) before income taxes									(151,678)	(101,628)	(143,178)
Depreciation and amortization									5,313	5,946	9,180
Assets	639,844				686,594				639,844	686,594	714,069
Liabilities	3,200,497				2,349,722				3,200,497	2,349,722	2,497,750
Operating Segment \| Other. \| Other segments
Segment Reporting Information
Total net sales									27,496	26,954	17,698
Operating Segment \| Other. \| U.S.
Segment Reporting Information
Total net sales									94,377	87,532	69,307
Operating Segment \| Other. \| Non-U.S.
Segment Reporting Information
Total net sales									1,113	840	457
Eliminations
Segment Reporting Information
Total net sales									(1,589,661)	(1,425,946)	(1,481,538)
Operating income (loss)									4,428	(948)	(3,252)
Income (loss) before income taxes									4,428	(948)	(3,252)
Depreciation and amortization									(204)	(204)	(204)
Assets	(206,437)				(216,295)				(206,437)	(216,295)	(194,868)
Liabilities	(196,468)				(203,945)				(196,468)	(203,945)	(184,341)
Eliminations \| Other segments
Segment Reporting Information
Total net sales									$ (1,589,661)	$ (1,425,946)	$ (1,481,538)