Condensed Consolidating Information (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Condensed Consolidating Financial Statements
Net sales	$ 1,982,040	$ 2,015,969
Costs of goods sold	1,780,776	1,720,215
Gross profit (loss)	201,264	295,754
Selling, general and administrative	81,448	90,428
Operating income (loss)	119,816	205,326
Interest expense, net of capitalized interest	41,112	43,346
Other (income) expense, net	10,248	(4,567)
Income (loss) before income taxes and equity in net income of subsidiaries	68,456	166,547
Income taxes (benefit)	26,679	62,317
Net income (loss)	41,777	104,230
Net loss attributable to noncontrolling interests	3,898	1,673
Net income attributable to Steel Dynamics, Inc.	45,675	105,903
Parent
Condensed Consolidating Financial Statements
Net sales	913,193	912,817
Costs of goods sold	785,567	729,541
Gross profit (loss)	127,626	183,276
Selling, general and administrative	27,566	36,664
Operating income (loss)	100,060	146,612
Interest expense, net of capitalized interest	27,217	25,696
Other (income) expense, net	10,769	(3,179)
Income (loss) before income taxes and equity in net income of subsidiaries	62,074	124,095
Income taxes (benefit)	15,870	40,929
Net income (loss)	46,204	83,166
Equity in net loss of subsidiaries	(4,427)	22,737
Net income attributable to Steel Dynamics, Inc.	41,777	105,903
Guarantors
Condensed Consolidating Financial Statements
Net sales	2,308,156	2,301,547
Costs of goods sold	2,198,898	2,165,378
Gross profit (loss)	109,258	136,169
Selling, general and administrative	54,555	55,893
Operating income (loss)	54,703	80,276
Interest expense, net of capitalized interest	13,606	17,262
Other (income) expense, net	(1,064)	(2,675)
Income (loss) before income taxes and equity in net income of subsidiaries	42,161	65,689
Income taxes (benefit)	16,134	24,904
Net income (loss)	26,027	40,785
Net income attributable to Steel Dynamics, Inc.	26,027	40,785
Combined Non-Guarantors
Condensed Consolidating Financial Statements
Net sales	46,835	47,522
Costs of goods sold	63,894	57,595
Gross profit (loss)	(17,059)	(10,073)
Selling, general and administrative	2,459	2,122
Operating income (loss)	(19,518)	(12,195)
Interest expense, net of capitalized interest	1,710	2,314
Other (income) expense, net	(877)	(718)
Income (loss) before income taxes and equity in net income of subsidiaries	(20,351)	(13,791)
Income taxes (benefit)	353	43
Net income (loss)	(20,704)	(13,834)
Net loss attributable to noncontrolling interests	3,898	1,673
Net income attributable to Steel Dynamics, Inc.	(16,806)	(12,161)
Consolidating Adjustments
Condensed Consolidating Financial Statements
Net sales	(1,286,144)	(1,245,917)
Costs of goods sold	(1,267,583)	(1,232,299)
Gross profit (loss)	(18,561)	(13,618)
Selling, general and administrative	(3,132)	(4,251)
Operating income (loss)	(15,429)	(9,367)
Interest expense, net of capitalized interest	(1,421)	(1,926)
Other (income) expense, net	1,420	2,005
Income (loss) before income taxes and equity in net income of subsidiaries	(15,428)	(9,446)
Income taxes (benefit)	(5,678)	(3,559)
Net income (loss)	(9,750)	(5,887)
Equity in net loss of subsidiaries	4,427	(22,737)
Net income attributable to Steel Dynamics, Inc.	$ (5,323)	$ (28,624)