Segment Information - Results (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Segment Reporting Information
Total net sales	$ 2,023,902	$ 2,005,007	$ 3,765,203	$ 4,052,442
Operating income (loss)	256,122	77,559	388,087	177,330
Income (loss) before income taxes	221,294	41,608	318,008	82,100
Depreciation and amortization	74,795	74,273	148,780	147,095
Capital expenditures	35,686	22,821	63,394	56,172
Assets	6,629,676	6,826,763	6,629,676	6,826,763	$ 6,202,082
U.S.
Segment Reporting Information
Total net sales	1,926,905	1,887,361	3,575,298	3,811,335
Non-U.S.
Segment Reporting Information
Total net sales	96,997	117,646	189,905	241,107
Operating Segment
Segment Reporting Information
Total net sales	2,023,902	2,005,007	3,765,203	4,052,442
Operating Segment | Steel Operations
Segment Reporting Information
Total net sales	1,533,298	1,429,237	2,791,686	2,863,559
Operating income (loss)	273,111	99,013	405,386	213,978
Income (loss) before income taxes	250,683	77,290	360,058	166,621
Depreciation and amortization	53,675	51,242	106,158	102,212
Capital expenditures	30,098	14,149	54,002	30,349
Assets	3,992,230	4,127,487	3,992,230	4,127,487
Operating Segment | Steel Operations | Other segments
Segment Reporting Information
Total net sales	66,594	53,560	107,806	102,463
Operating Segment | Steel Operations | U.S.
Segment Reporting Information
Total net sales	1,408,993	1,303,278	2,565,962	2,616,704
Operating Segment | Steel Operations | Non-U.S.
Segment Reporting Information
Total net sales	57,711	72,399	117,918	144,392
Operating Segment | Metals Recycling Operations
Segment Reporting Information
Total net sales	590,724	645,449	1,077,909	1,297,460
Operating income (loss)	11,093	8,282	13,860	3,784
Income (loss) before income taxes	8,086	4,723	7,863	(5,813)
Depreciation and amortization	14,250	17,014	28,830	34,294
Capital expenditures	4,482	4,632	7,562	11,047
Assets	1,076,596	1,666,384	1,076,596	1,666,384
Operating Segment | Metals Recycling Operations | Other segments
Segment Reporting Information
Total net sales	279,664	254,238	497,442	480,654
Operating Segment | Metals Recycling Operations | U.S.
Segment Reporting Information
Total net sales	271,985	346,103	508,742	720,395
Operating Segment | Metals Recycling Operations | Non-U.S.
Segment Reporting Information
Total net sales	39,075	45,108	71,725	96,411
Operating Segment | Steel Fabrication Operations
Segment Reporting Information
Total net sales	171,720	154,525	351,801	315,553
Operating income (loss)	23,470	27,660	55,486	49,021
Income (loss) before income taxes	21,514	25,879	51,530	45,473
Depreciation and amortization	2,762	2,158	5,583	4,388
Capital expenditures	567	534	1,171	1,571
Assets	334,530	295,642	334,530	295,642
Operating Segment | Steel Fabrication Operations | Other segments
Segment Reporting Information
Total net sales	1,178	12	1,204	16
Operating Segment | Steel Fabrication Operations | U.S.
Segment Reporting Information
Total net sales	170,477	154,513	350,518	315,537
Operating Segment | Steel Fabrication Operations | Non-U.S.
Segment Reporting Information
Total net sales	65		79
Operating Segment | Other
Segment Reporting Information
Total net sales	76,865	90,308	152,754	183,908
Operating income (loss)	(45,569)	(52,970)	(77,499)	(88,872)
Income (loss) before income taxes	(53,006)	(61,858)	(92,297)	(123,600)
Depreciation and amortization	4,160	3,910	8,312	6,303
Capital expenditures	539	3,506	659	13,205
Assets	1,348,290	869,929	1,348,290	869,929
Operating Segment | Other | Other segments
Segment Reporting Information
Total net sales	1,269	6,702	2,495	24,905
Operating Segment | Other | U.S.
Segment Reporting Information
Total net sales	75,450	83,467	150,076	158,699
Operating Segment | Other | Non-U.S.
Segment Reporting Information
Total net sales	146	139	183	304
Eliminations
Segment Reporting Information
Total net sales	(348,705)	(314,512)	(608,947)	(608,038)
Operating income (loss)	(5,983)	(4,426)	(9,146)	(581)
Income (loss) before income taxes	(5,983)	(4,426)	(9,146)	(581)
Depreciation and amortization	(52)	(51)	(103)	(102)
Assets	(121,970)	(132,679)	(121,970)	(132,679)
Eliminations | Other segments
Segment Reporting Information
Total net sales	$ (348,705)	$ (314,512)	$ (608,947)	$ (608,038)