Segment Information - Results (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) segment	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Segment Reporting Information
Number of reporting segments | segment									3
Total net sales	$ 1,591,046	$ 1,950,923	$ 2,005,007	$ 2,047,435	$ 2,517,093	$ 2,339,016	$ 2,069,761	$ 1,830,082	$ 7,594,411	$ 8,755,952	$ 7,372,924
Operating income (loss)	(381,143)	$ 131,029	$ 77,559	$ 99,771	(81,160)	$ 188,643	$ 131,905	$ 80,932	(72,784)	320,320	386,525
Income (loss) before income taxes									(242,117)	164,803	262,830
Depreciation and amortization									294,595	263,325	230,928
Capital expenditures									114,501	111,785	186,843
Assets	6,202,082				7,233,159				6,202,082	7,233,159	5,888,534
Liabilities	3,530,631				4,311,292				3,530,631	4,311,292	3,276,165
U.S.
Segment Reporting Information
Total net sales									7,139,898	8,272,958	6,955,726
Non-U.S.
Segment Reporting Information
Total net sales									454,513	482,994	417,198
Steel Operations
Segment Reporting Information
Capital expenditures									71,752	62,807	126,772
Metals Recycling Operations
Segment Reporting Information
Capital expenditures									21,874	22,223	32,354
Steel Fabrication Operations
Segment Reporting Information
Capital expenditures									3,395	3,027	2,166
Steel Fabrication Operations | Non-U.S.
Segment Reporting Information
Total net sales									2,051
Other
Segment Reporting Information
Capital expenditures									17,480	23,728	25,551
Operating Segment
Segment Reporting Information
Total net sales									7,594,411	8,755,952	7,372,924
Operating Segment | Steel Operations
Segment Reporting Information
Total net sales									5,422,475	5,821,578	4,684,847
Operating income (loss)									403,216	683,609	516,125
Income (loss) before income taxes									312,402	614,653	461,151
Depreciation and amortization									205,827	149,064	116,533
Assets	3,827,108				4,511,436				3,827,108	4,511,436	2,760,752
Liabilities	603,505				776,804				603,505	776,804	572,573
Operating Segment | Steel Operations | Other segments
Segment Reporting Information
Total net sales									218,963	279,835	223,390
Operating Segment | Steel Operations | U.S.
Segment Reporting Information
Total net sales									4,935,549	5,300,762	4,256,077
Operating Segment | Steel Operations | Non-U.S.
Segment Reporting Information
Total net sales									267,963	240,981	205,380
Operating Segment | Metals Recycling Operations
Segment Reporting Information
Total net sales									2,337,716	3,539,206	3,274,866
Operating income (loss)									(448,137)	26,014	41,949
Income (loss) before income taxes									(465,426)	5,670	15,831
Depreciation and amortization									65,640	75,242	80,483
Assets	1,067,672				1,767,820				1,067,672	1,767,820	1,840,490
Liabilities	250,719				352,271				250,719	352,271	364,231
Operating Segment | Metals Recycling Operations | Other segments
Segment Reporting Information
Total net sales									904,713	1,312,379	997,316
Operating Segment | Metals Recycling Operations | U.S.
Segment Reporting Information
Total net sales									1,249,061	1,985,927	2,066,572
Operating Segment | Metals Recycling Operations | Non-U.S.
Segment Reporting Information
Total net sales									183,942	240,900	210,978
Operating Segment | Steel Fabrication Operations
Segment Reporting Information
Total net sales									673,399	631,808	439,655
Operating income (loss)									115,947	51,894	7,003
Income (loss) before income taxes									108,795	45,376	827
Depreciation and amortization									9,587	9,712	8,736
Assets	341,276				301,156				341,276	301,156	270,160
Liabilities	88,439				42,074				88,439	42,074	22,648
Operating Segment | Steel Fabrication Operations | Other segments
Segment Reporting Information
Total net sales									25	58	1,401
Operating Segment | Steel Fabrication Operations | U.S.
Segment Reporting Information
Total net sales									671,323	631,750	438,254
Operating Segment | Other
Segment Reporting Information
Total net sales									314,847	468,505	299,079
Operating income (loss)									(148,784)	(445,549)	(177,939)
Income (loss) before income taxes									(202,862)	(505,248)	(214,366)
Depreciation and amortization									13,746	29,512	25,381
Assets	1,050,506				793,389				1,050,506	793,389	1,106,856
Liabilities	2,667,189				3,270,878				2,667,189	3,270,878	2,394,072
Operating Segment | Other | Other segments
Segment Reporting Information
Total net sales									30,325	112,873	103,416
Operating Segment | Other | U.S.
Segment Reporting Information
Total net sales									283,965	354,519	194,823
Operating Segment | Other | Non-U.S.
Segment Reporting Information
Total net sales									557	1,113	840
Eliminations
Segment Reporting Information
Total net sales									(1,154,026)	(1,705,145)	(1,325,523)
Operating income (loss)									4,974	4,352	(613)
Income (loss) before income taxes									4,974	4,352	(613)
Depreciation and amortization									(205)	(205)	(205)
Assets	(84,480)				(140,642)				(84,480)	(140,642)	(89,724)
Liabilities	$ (79,221)				$ (130,735)				(79,221)	(130,735)	(77,359)
Eliminations | Other segments
Segment Reporting Information
Total net sales									$ (1,154,026)	$ (1,705,145)	$ (1,325,523)