Condensed Consolidating Information (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Condensed Consolidating Statements of Operations
Net sales	$ 2,069,761	$ 1,801,340	$ 3,899,843	$ 3,597,036
Costs of goods sold	1,846,990	1,653,648	3,513,768	3,273,080
Gross profit	222,771	147,692	386,075	323,956
Selling, general and administrative	90,866	78,494	173,238	158,526
Operating income	131,905	69,198	212,837	165,430
Interest expense, net of capitalized interest	30,050	31,465	60,619	66,094
Other (income) expense, net	(1,754)	(1,246)	(2,385)	(2,292)
Income before income taxes	103,609	38,979	154,603	101,628
Income taxes (benefit)	37,268	15,706	54,564	37,103
Net income	66,341	23,273	100,039	64,525
Net loss attributable to noncontrolling interests	5,962	5,685	10,843	12,648
Net income attributable to Steel Dynamics, Inc.	72,303	28,958	110,882	77,173
Reportable Legal Entities [Member] | Parent Company [Member]
Condensed Consolidating Statements of Operations
Net sales	1,007,569	836,805	1,871,132	1,664,006
Costs of goods sold	860,024	753,761	1,621,419	1,460,148
Gross profit	147,545	83,044	249,713	203,858
Selling, general and administrative	35,419	24,916	64,253	53,602
Operating income	112,126	58,128	185,460	150,256
Interest expense, net of capitalized interest	19,031	20,148	38,392	42,194
Other (income) expense, net	(1,556)	(1,533)	(2,532)	(2,353)
Income before income taxes	94,651	39,513	149,600	110,415
Income taxes (benefit)	23,950	5,621	33,875	17,015
Net income	70,701	33,892	115,725	93,400
Equity in net loss of subsidiaries	1,602	(4,934)	(4,843)	(16,227)
Net income attributable to Steel Dynamics, Inc.	72,303	28,958	110,882	77,173
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Consolidating Statements of Operations
Net sales	2,313,459	1,998,513	4,425,848	4,014,000
Costs of goods sold	2,183,181	1,900,497	4,198,757	3,814,555
Gross profit	130,278	98,016	227,091	199,445
Selling, general and administrative	56,411	54,764	110,700	108,756
Operating income	73,867	43,252	116,391	90,689
Interest expense, net of capitalized interest	10,294	10,751	20,855	22,790
Other (income) expense, net	(46)	214	349	14
Income before income taxes	63,619	32,287	95,187	67,885
Income taxes (benefit)	23,076	12,214	34,018	25,133
Net income	40,543	20,073	61,169	42,752
Net income attributable to Steel Dynamics, Inc.	40,543	20,073	61,169	42,752
Reportable Legal Entities [Member] | Non Guarantor Subsidiaries [Member]
Condensed Consolidating Statements of Operations
Net sales	121,239	88,039	227,088	154,409
Costs of goods sold	141,362	107,814	264,935	203,755
Gross profit	(20,123)	(19,775)	(37,847)	(49,346)
Selling, general and administrative	3,406	2,673	6,814	4,811
Operating income	(23,529)	(22,448)	(44,661)	(54,157)
Interest expense, net of capitalized interest	1,986	1,789	3,866	3,490
Other (income) expense, net	(1,412)	(1,149)	(2,696)	(2,332)
Income before income taxes	(24,103)	(23,088)	(45,831)	(55,315)
Income taxes (benefit)	814	1,382	1,510	2,081
Net income	(24,917)	(24,470)	(47,341)	(57,396)
Net loss attributable to noncontrolling interests	5,962	5,685	10,843	12,648
Net income attributable to Steel Dynamics, Inc.	(18,955)	(18,785)	(36,498)	(44,748)
Consolidation Eliminations [Member]
Condensed Consolidating Statements of Operations
Net sales	(1,372,506)	(1,122,017)	(2,624,225)	(2,235,379)
Costs of goods sold	(1,337,577)	(1,108,424)	(2,571,343)	(2,205,378)
Gross profit	(34,929)	(13,593)	(52,882)	(30,001)
Selling, general and administrative	(4,370)	(3,859)	(8,529)	(8,643)
Operating income	(30,559)	(9,734)	(44,353)	(21,358)
Interest expense, net of capitalized interest	(1,261)	(1,223)	(2,494)	(2,380)
Other (income) expense, net	1,260	1,222	2,494	2,379
Income before income taxes	(30,558)	(9,733)	(44,353)	(21,357)
Income taxes (benefit)	(10,572)	(3,511)	(14,839)	(7,126)
Net income	(19,986)	(6,222)	(29,514)	(14,231)
Equity in net loss of subsidiaries	(1,602)	4,934	4,843	16,227
Net income attributable to Steel Dynamics, Inc.	$ (21,588)	$ (1,288)	$ (24,671)	$ 1,996