Condensed Consolidating Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Condensed Consolidating Financial Statements
Ownership interest in subsidiaries (as a percent)	100.00%
Cash and equivalents	$ 390,761	$ 186,513	$ 9,008	$ 16,233
Investment in short-term commercial paper	84,830
Accounts receivable, net	722,791	622,189
Inventories	1,199,584	1,114,063
Other current assets	57,292	77,238
Total current assets	2,455,258	2,000,003
Property, plant and equipment, net	2,193,745	2,213,333
Intangible assets, net	450,893	489,240
Goodwill	745,066	751,675
Other assets, including investments in subs	134,264	135,683
Total assets	5,979,226	5,589,934	5,129,872
Accounts payable	420,824	348,601
Accrued expenses	235,515	203,792
Current maturities of long-term debt	444,078	8,924
Total current liabilities	1,100,417	561,317
Long-term debt	1,936,022	2,377,897
Other liabilities	572,193	519,591
Redeemable noncontrolling interests	70,694	54,294
Common stock	636	633
Treasury stock	(722,653)	(727,624)
Additional paid-in capital	1,026,157	998,728
Retained earnings (deficit)	2,011,801	1,821,133
Total Steel Dynamics, Inc. equity	2,315,941	2,092,870
Noncontrolling interests	(16,041)	(16,035)
Total equity	2,299,900	2,076,835	2,003,265	1,632,313
Total liabilities and equity	5,979,226	5,589,934
Parent
Condensed Consolidating Financial Statements
Cash and equivalents	301,073	173,563	430	1,389
Investment in short-term commercial paper	84,830
Accounts receivable, net	319,995	283,883
Inventories	584,079	548,726
Other current assets	83,116	96,040
Total current assets	1,373,093	1,102,212
Property, plant and equipment, net	1,059,011	1,110,350
Other assets, including investments in subs	2,791,718	2,788,097
Total assets	5,223,822	5,000,659
Accounts payable	155,220	127,246
Accrued expenses	157,868	123,498
Current maturities of long-term debt	439,199	7,554
Total current liabilities	752,287	258,298
Long-term debt	1,905,199	2,344,399
Other liabilities	250,395	305,092
Common stock	636	633
Treasury stock	(722,653)	(727,624)
Additional paid-in capital	1,026,157	998,728
Retained earnings (deficit)	2,011,801	1,821,133
Total Steel Dynamics, Inc. equity	2,315,941	2,092,870
Total equity	2,315,941	2,092,870
Total liabilities and equity	5,223,822	5,000,659
Guarantors
Condensed Consolidating Financial Statements
Cash and equivalents	58,699	10,628	6,362	11,514
Accounts receivable, net	726,192	614,412
Inventories	533,022	487,298
Other current assets	4,119	9,757
Total current assets	1,322,032	1,122,095
Property, plant and equipment, net	660,048	684,118
Intangible assets, net	450,893	489,240
Goodwill	745,066	751,675
Other assets, including investments in subs	33,507	36,617
Total assets	3,211,546	3,083,745
Accounts payable	273,049	227,823
Accrued expenses	98,498	102,114
Current maturities of long-term debt	300	325
Total current liabilities	371,847	330,262
Other liabilities	2,132,778	2,158,725
Common stock	33,896	33,901
Additional paid-in capital	117,737	117,737
Retained earnings (deficit)	555,288	443,120
Total Steel Dynamics, Inc. equity	706,921	594,758
Total equity	706,921	594,758
Total liabilities and equity	3,211,546	3,083,745
Combined Non-Guarantors
Condensed Consolidating Financial Statements
Cash and equivalents	30,989	2,322	2,216	3,330
Accounts receivable, net	8,971	7,282
Inventories	85,046	84,183
Other current assets	2,304	3,444
Total current assets	127,310	97,231
Property, plant and equipment, net	477,514	421,897
Other assets, including investments in subs	9,853	7,601
Total assets	614,677	526,729
Accounts payable	23,195	26,015
Accrued expenses	10,012	8,497
Current maturities of long-term debt	53,551	34,604
Total current liabilities	86,758	69,116
Long-term debt	169,797	168,278
Other liabilities	51,625	27,072
Redeemable noncontrolling interests	70,694	54,294
Common stock	18,121	16,121
Additional paid-in capital	347,151	256,905
Retained earnings (deficit)	(113,428)	(49,022)
Total Steel Dynamics, Inc. equity	251,844	224,004
Noncontrolling interests	(16,041)	(16,035)
Total equity	235,803	207,969
Total liabilities and equity	614,677	526,729
Consolidating Adjustments
Condensed Consolidating Financial Statements
Accounts receivable, net	(332,367)	(283,388)
Inventories	(2,563)	(6,144)
Other current assets	(32,247)	(32,003)
Total current assets	(367,177)	(321,535)
Property, plant and equipment, net	(2,828)	(3,032)
Other assets, including investments in subs	(2,700,814)	(2,696,632)
Total assets	(3,070,819)	(3,021,199)
Accounts payable	(30,640)	(32,483)
Accrued expenses	(30,863)	(30,317)
Current maturities of long-term debt	(48,972)	(33,559)
Total current liabilities	(110,475)	(96,359)
Long-term debt	(138,974)	(134,780)
Other liabilities	(1,862,605)	(1,971,298)
Common stock	(52,017)	(50,022)
Additional paid-in capital	(464,888)	(374,642)
Retained earnings (deficit)	(441,860)	(394,098)
Total Steel Dynamics, Inc. equity	(958,765)	(818,762)
Total equity	(958,765)	(818,762)
Total liabilities and equity	$ (3,070,819)	$ (3,021,199)