Condensed Consolidating Information (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Condensed Consolidating Financial Statements
Net sales	$ 1,795,696	$ 1,982,040
Costs of goods sold	1,619,432	1,780,776
Gross profit	176,264	201,264
Selling, general and administrative	80,032	81,448
Operating income	96,232	119,816
Interest expense, net of capitalized interest	34,629	41,112
Other (income) expense, net	(1,046)	10,248
Income before income taxes	62,649	68,456
Income taxes (benefit)	21,397	26,679
Net income	41,252	41,777
Net loss attributable to noncontrolling interests	6,963	3,898
Net income attributable to Steel Dynamics, Inc.	48,215	45,675
Parent
Condensed Consolidating Financial Statements
Net sales	827,201	913,193
Costs of goods sold	706,387	785,567
Gross profit	120,814	127,626
Selling, general and administrative	28,686	27,566
Operating income	92,128	100,060
Interest expense, net of capitalized interest	22,046	27,217
Other (income) expense, net	(820)	10,769
Income before income taxes	70,902	62,074
Income taxes (benefit)	11,394	15,870
Net income	59,508	46,204
Equity in net loss of subsidiaries	(11,293)	(4,427)
Net income attributable to Steel Dynamics, Inc.	48,215	41,777
Guarantors
Condensed Consolidating Financial Statements
Net sales	2,015,487	2,308,156
Costs of goods sold	1,914,058	2,198,898
Gross profit	101,429	109,258
Selling, general and administrative	53,992	54,555
Operating income	47,437	54,703
Interest expense, net of capitalized interest	12,039	13,606
Other (income) expense, net	(200)	(1,064)
Income before income taxes	35,598	42,161
Income taxes (benefit)	12,919	16,134
Net income	22,679	26,027
Net income attributable to Steel Dynamics, Inc.	22,679	26,027
Combined Non-Guarantors
Condensed Consolidating Financial Statements
Net sales	66,370	46,835
Costs of goods sold	95,941	63,894
Gross profit	(29,571)	(17,059)
Selling, general and administrative	2,138	2,459
Operating income	(31,709)	(19,518)
Interest expense, net of capitalized interest	1,701	1,710
Other (income) expense, net	(1,183)	(877)
Income before income taxes	(32,227)	(20,351)
Income taxes (benefit)	699	353
Net income	(32,926)	(20,704)
Net loss attributable to noncontrolling interests	6,963	3,898
Net income attributable to Steel Dynamics, Inc.	(25,963)	(16,806)
Consolidating Adjustments
Condensed Consolidating Financial Statements
Net sales	(1,113,362)	(1,286,144)
Costs of goods sold	(1,096,954)	(1,267,583)
Gross profit	(16,408)	(18,561)
Selling, general and administrative	(4,784)	(3,132)
Operating income	(11,624)	(15,429)
Interest expense, net of capitalized interest	(1,157)	(1,421)
Other (income) expense, net	1,157	1,420
Income before income taxes	(11,624)	(15,428)
Income taxes (benefit)	(3,615)	(5,678)
Net income	(8,009)	(9,750)
Equity in net loss of subsidiaries	11,293	4,427
Net income attributable to Steel Dynamics, Inc.	$ 3,284	$ (5,323)