Condensed Consolidating Information (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Condensed Consolidating Financial Statements
Net sales	$ 1,801,340	$ 1,909,803	$ 3,597,036	$ 3,891,843
Costs of goods sold	1,653,648	1,727,667	3,273,080	3,508,443
Gross profit	147,692	182,136	323,956	383,400
Selling, general and administrative	78,494	78,437	158,526	159,885
Operating income	69,198	103,699	165,430	223,515
Interest expense, net of capitalized interest	31,465	41,106	66,094	82,218
Other (income) expense, net	(1,246)	(1,892)	(2,292)	8,356
Income before income taxes	38,979	64,485	101,628	132,941
Income taxes (benefit)	15,706	25,180	37,103	51,859
Net income	23,273	39,305	64,525	81,082
Net loss attributable to noncontrolling interests	5,685	5,167	12,648	9,065
Net income attributable to Steel Dynamics, Inc.	28,958	44,472	77,173	90,147
Parent
Condensed Consolidating Financial Statements
Net sales	836,805	926,791	1,664,006	1,839,984
Costs of goods sold	753,761	804,586	1,460,148	1,590,153
Gross profit	83,044	122,205	203,858	249,831
Selling, general and administrative	24,916	24,703	53,602	52,269
Operating income	58,128	97,502	150,256	197,562
Interest expense, net of capitalized interest	20,148	27,213	42,194	54,430
Other (income) expense, net	(1,533)	(2,695)	(2,353)	8,074
Income before income taxes	39,513	72,984	110,415	135,058
Income taxes (benefit)	5,621	18,710	17,015	34,580
Net income	33,892	54,274	93,400	100,478
Equity in net loss of subsidiaries	(4,934)	(9,802)	(16,227)	(10,331)
Net income attributable to Steel Dynamics, Inc.	28,958	44,472	77,173	90,147
Guarantors
Condensed Consolidating Financial Statements
Net sales	1,998,513	2,181,236	4,014,000	4,489,392
Costs of goods sold	1,900,497	2,084,159	3,814,555	4,283,057
Gross profit	98,016	97,077	199,445	206,335
Selling, general and administrative	54,764	52,935	108,756	107,490
Operating income	43,252	44,142	90,689	98,845
Interest expense, net of capitalized interest	10,751	13,605	22,790	27,211
Other (income) expense, net	214	194	14	(870)
Income before income taxes	32,287	30,343	67,885	72,504
Income taxes (benefit)	12,214	11,552	25,133	27,686
Net income	20,073	18,791	42,752	44,818
Net income attributable to Steel Dynamics, Inc.	20,073	18,791	42,752	44,818
Combined Non-Guarantors
Condensed Consolidating Financial Statements
Net sales	88,039	36,022	154,409	82,857
Costs of goods sold	107,814	56,063	203,755	119,957
Gross profit	(19,775)	(20,041)	(49,346)	(37,100)
Selling, general and administrative	2,673	4,449	4,811	6,908
Operating income	(22,448)	(24,490)	(54,157)	(44,008)
Interest expense, net of capitalized interest	1,789	1,739	3,490	3,449
Other (income) expense, net	(1,149)	(844)	(2,332)	(1,721)
Income before income taxes	(23,088)	(25,385)	(55,315)	(45,736)
Income taxes (benefit)	1,382	18	2,081	371
Net income	(24,470)	(25,403)	(57,396)	(46,107)
Net loss attributable to noncontrolling interests	5,685	5,167	12,648	9,065
Net income attributable to Steel Dynamics, Inc.	(18,785)	(20,236)	(44,748)	(37,042)
Consolidating Adjustments
Condensed Consolidating Financial Statements
Net sales	(1,122,017)	(1,234,246)	(2,235,379)	(2,520,390)
Costs of goods sold	(1,108,424)	(1,217,141)	(2,205,378)	(2,484,724)
Gross profit	(13,593)	(17,105)	(30,001)	(35,666)
Selling, general and administrative	(3,859)	(3,650)	(8,643)	(6,782)
Operating income	(9,734)	(13,455)	(21,358)	(28,884)
Interest expense, net of capitalized interest	(1,223)	(1,451)	(2,380)	(2,872)
Other (income) expense, net	1,222	1,453	2,379	2,873
Income before income taxes	(9,733)	(13,457)	(21,357)	(28,885)
Income taxes (benefit)	(3,511)	(5,100)	(7,126)	(10,778)
Net income	(6,222)	(8,357)	(14,231)	(18,107)
Equity in net loss of subsidiaries	4,934	9,802	16,227	10,331
Net income attributable to Steel Dynamics, Inc.	$ (1,288)	$ 1,445	$ 1,996	$ (7,776)