Condensed Consolidating Information (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Condensed Consolidating Financial Statements
Net sales	$ 1,693,390	$ 2,043,455	$ 5,585,233	$ 6,139,155
Costs of goods sold	1,536,989	1,844,212	5,045,432	5,367,772
Gross profit (loss)	156,401	199,243	539,801	771,383
Selling, general and administrative	83,680	90,458	243,565	269,053
Operating income (loss)	72,721	108,785	296,236	502,330
Interest expense, net of capitalized interest	41,490	44,702	123,708	132,860
Other (income) expense, net	24,010	(3,523)	32,366	(13,835)
Income (loss) before income taxes and equity in net income of subsidiaries	7,221	67,606	140,162	383,305
Income taxes (benefit)	1,116	27,749	52,975	143,392
Net income (loss)	6,105	39,857	87,187	239,913
Net loss attributable to noncontrolling interests	6,728	3,447	15,793	8,004
Net income attributable to Steel Dynamics, Inc.	12,833	43,304	102,980	247,917
Parent
Condensed Consolidating Financial Statements
Net sales	785,168	932,793	2,625,152	2,798,097
Costs of goods sold	685,074	809,684	2,275,227	2,293,661
Gross profit (loss)	100,094	123,109	349,925	504,436
Selling, general and administrative	19,927	37,678	72,196	109,870
Operating income (loss)	80,167	85,431	277,729	394,566
Interest expense, net of capitalized interest	27,153	26,163	81,583	77,984
Other (income) expense, net	23,345	(3,232)	31,419	(10,115)
Income (loss) before income taxes and equity in net income of subsidiaries	29,669	62,500	164,727	326,697
Income taxes (benefit)	(2,771)	19,524	31,809	103,264
Net income (loss)	32,440	42,976	132,918	223,433
Equity in net income of subsidiaries	(19,607)	328	(29,938)	24,484
Net income attributable to Steel Dynamics, Inc.	12,833	43,304	102,980	247,917
Guarantors
Condensed Consolidating Financial Statements
Net sales	1,918,774	2,309,239	6,408,166	6,955,744
Costs of goods sold	1,823,447	2,194,687	6,106,504	6,599,291
Gross profit (loss)	95,327	114,552	301,662	356,453
Selling, general and administrative	53,023	53,755	160,513	163,742
Operating income (loss)	42,304	60,797	141,149	192,711
Interest expense, net of capitalized interest	13,997	18,237	41,208	53,763
Other (income) expense, net	434	(1,895)	(436)	(7,659)
Income (loss) before income taxes and equity in net income of subsidiaries	27,873	44,455	100,377	146,607
Income taxes (benefit)	8,668	16,023	36,354	54,695
Net income (loss)	19,205	28,432	64,023	91,912
Net income attributable to Steel Dynamics, Inc.	19,205	28,432	64,023	91,912
Combined Non-Guarantors
Condensed Consolidating Financial Statements
Net sales	48,167	45,407	131,024	143,872
Costs of goods sold	69,520	60,673	189,477	184,424
Gross profit (loss)	(21,353)	(15,266)	(58,453)	(40,552)
Selling, general and administrative	14,032	2,475	20,940	6,545
Operating income (loss)	(35,385)	(17,741)	(79,393)	(47,097)
Interest expense, net of capitalized interest	1,619	2,343	5,068	7,070
Other (income) expense, net	(1,046)	(437)	(2,767)	(2,123)
Income (loss) before income taxes and equity in net income of subsidiaries	(35,958)	(19,647)	(81,694)	(52,044)
Income taxes (benefit)	73	(247)	444	(260)
Net income (loss)	(36,031)	(19,400)	(82,138)	(51,784)
Net loss attributable to noncontrolling interests	6,728	3,447	15,793	8,004
Net income attributable to Steel Dynamics, Inc.	(29,303)	(15,953)	(66,345)	(43,780)
Consolidating Adjustments
Condensed Consolidating Financial Statements
Net sales	(1,058,719)	(1,243,984)	(3,579,109)	(3,758,558)
Costs of goods sold	(1,041,052)	(1,220,832)	(3,525,776)	(3,709,604)
Gross profit (loss)	(17,667)	(23,152)	(53,333)	(48,954)
Selling, general and administrative	(3,302)	(3,450)	(10,084)	(11,104)
Operating income (loss)	(14,365)	(19,702)	(43,249)	(37,850)
Interest expense, net of capitalized interest	(1,279)	(2,041)	(4,151)	(5,957)
Other (income) expense, net	1,277	2,041	4,150	6,062
Income (loss) before income taxes and equity in net income of subsidiaries	(14,363)	(19,702)	(43,248)	(37,955)
Income taxes (benefit)	(4,854)	(7,551)	(15,632)	(14,307)
Net income (loss)	(9,509)	(12,151)	(27,616)	(23,648)
Equity in net income of subsidiaries	19,607	(328)	29,938	(24,484)
Net income attributable to Steel Dynamics, Inc.	$ 10,098	$ (12,479)	$ 2,322	$ (48,132)