Segment Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) segment	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Segment Reporting Information
Number of reporting segments | segment			3
Total net sales	$ 2,005,007	$ 2,069,761	$ 4,052,442	$ 3,899,843
Operating income (loss)	77,559	131,905	177,330	212,837
Income (loss) before income taxes	41,608	103,609	82,100	154,603
Depreciation and amortization	74,273	58,441	147,095	116,009
Capital expenditures	22,821	33,534	56,172	58,375
Assets	6,826,763	5,985,202	6,826,763	5,985,202	$ 7,311,027
Liabilities	3,902,063	3,025,992	3,902,063	3,025,992
U.S.
Segment Reporting Information
Total net sales	1,887,360	1,960,665	3,811,335	3,676,183
Non-U.S.
Segment Reporting Information
Total net sales	117,647	109,096	241,107	223,660
Steel Operations
Segment Reporting Information
Capital expenditures	9,762	16,332	24,448	34,938
Metals Recycling and Ferrous Resources Operations
Segment Reporting Information
Capital expenditures	12,121	16,384	29,779	22,163
Steel Fabrication Operations
Segment Reporting Information
Capital expenditures	534	536	1,571	847
Other.
Segment Reporting Information
Capital expenditures	404	282	374	427
Operating Segment
Segment Reporting Information
Total net sales	2,005,007	2,069,761	4,052,442	3,899,843
Operating Segment | Steel Operations
Segment Reporting Information
Total net sales	1,429,237	1,334,906	2,863,559	2,496,236
Operating income (loss)	107,761	155,949	219,301	261,592
Income (loss) before income taxes	86,039	142,594	171,945	234,592
Depreciation and amortization	49,171	28,869	97,785	56,246
Assets	4,023,351	2,732,388	4,023,351	2,732,388
Liabilities	710,780	578,124	710,780	578,124
Operating Segment | Steel Operations | Other segments
Segment Reporting Information
Total net sales	53,560	69,802	102,463	113,534
Operating Segment | Steel Operations | U.S.
Segment Reporting Information
Total net sales	1,303,278	1,214,247	2,616,704	2,275,326
Operating Segment | Steel Operations | Non-U.S.
Segment Reporting Information
Total net sales	72,399	50,857	144,392	107,376
Operating Segment | Metals Recycling and Ferrous Resources Operations
Segment Reporting Information
Total net sales	680,113	948,833	1,385,905	1,868,535
Operating income (loss)	(35,182)	(6,053)	(52,248)	(21,572)
Income (loss) before income taxes	(40,312)	(12,634)	(64,982)	(35,330)
Depreciation and amortization	21,775	25,870	42,613	52,491
Assets	2,023,082	2,551,899	2,023,082	2,551,899
Liabilities	541,396	640,459	541,396	640,459
Operating Segment | Metals Recycling and Ferrous Resources Operations | Other segments
Segment Reporting Information
Total net sales	218,480	303,617	445,558	647,545
Operating Segment | Metals Recycling and Ferrous Resources Operations | U.S.
Segment Reporting Information
Total net sales	416,525	587,385	843,936	1,105,342
Operating Segment | Metals Recycling and Ferrous Resources Operations | Non-U.S.
Segment Reporting Information
Total net sales	45,108	57,831	96,411	115,648
Operating Segment | Steel Fabrication Operations
Segment Reporting Information
Total net sales	154,525	134,852	315,553	250,713
Operating income (loss)	27,660	7,590	49,021	10,716
Income (loss) before income taxes	25,879	6,099	45,473	7,751
Depreciation and amortization	2,158	2,401	4,388	4,623
Assets	295,642	297,149	295,642	297,149
Liabilities	57,566	20,879	57,566	20,879
Operating Segment | Steel Fabrication Operations | Other segments
Segment Reporting Information
Total net sales	12		16
Operating Segment | Steel Fabrication Operations | U.S.
Segment Reporting Information
Total net sales	154,513	134,852	315,537	250,713
Operating Segment | Other.
Segment Reporting Information
Total net sales	19,157	31,898	48,124	59,420
Operating income (loss)	(18,191)	(24,159)	(38,111)	(40,704)
Income (loss) before income taxes	(25,508)	(31,028)	(69,702)	(55,215)
Depreciation and amortization	1,221	1,352	2,411	2,751
Assets	693,993	624,518	693,993	624,518
Liabilities	2,792,947	1,996,306	2,792,947	1,996,306
Operating Segment | Other. | Other segments
Segment Reporting Information
Total net sales	5,973	7,309	12,662	13,982
Operating Segment | Other. | U.S.
Segment Reporting Information
Total net sales	13,044	24,181	35,158	44,802
Operating Segment | Other. | Non-U.S.
Segment Reporting Information
Total net sales	140	408	304	636
Eliminations
Segment Reporting Information
Total net sales	(278,025)	(380,728)	(560,699)	(775,061)
Operating income (loss)	(4,489)	(1,422)	(633)	2,805
Income (loss) before income taxes	(4,490)	(1,422)	(634)	2,805
Depreciation and amortization	(52)	(51)	(102)	(102)
Assets	(209,305)	(220,752)	(209,305)	(220,752)
Liabilities	(200,626)	(209,776)	(200,626)	(209,776)
Eliminations | Other segments
Segment Reporting Information
Total net sales	$ (278,025)	$ (380,728)	$ (560,699)	$ (775,061)