Condensed Consolidating Information (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009
Condensed Consolidating Financial Statements
Ownership interest in subsidiaries (as a percent)	100.00%
Cash and equivalents	$ 277,691	$ 160,810	$ 186,513	$ 191,593	$ 225,506	$ 9,008
Accounts receivable, net	849,401		622,189
Inventories	1,195,194		1,114,063
Other current assets	51,573		77,238
Total current assets	2,373,859		2,000,003
Property, plant and equipment, net	2,176,314		2,213,333
Intangible assets, net	469,719		489,240
Goodwill	748,383		751,675
Other assets, including investments in subsidiaries	132,178		135,683
Total assets	5,900,453		5,589,934	5,545,805
Accounts payable	455,859		348,601
Accrued expenses	213,435		203,792
Current maturities of long-term debt	1,552		8,924
Total current liabilities	670,846		561,317
Long-term debt	2,377,793		2,377,897
Other liabilities	540,326		519,591
Redeemable noncontrolling interest	54,294		54,294
Common stock	636		633
Treasury stock	(725,849)		(727,624)
Additional paid-in capital	1,019,061		998,728
Retained earnings	1,982,051		1,821,133
Total Steel Dynamics, Inc. equity	2,275,899		2,092,870
Noncontrolling interests	(18,705)		(16,035)
Total equity	2,257,194		2,076,835
Total liabilities and equity	5,900,453		5,589,934
Parent
Condensed Consolidating Financial Statements
Cash and equivalents	264,121		173,563	180,831		430
Accounts receivable, net	355,583		283,883
Inventories	604,523		548,726
Other current assets	74,566		96,040
Total current assets	1,298,793		1,102,212
Property, plant and equipment, net	1,081,980		1,110,350
Other assets, including investments in subsidiaries	2,809,475		2,788,097
Total assets	5,190,248		5,000,659
Accounts payable	147,054		127,246
Accrued expenses	136,489		123,498
Current maturities of long-term debt	432		7,554
Total current liabilities	283,975		258,298
Long-term debt	2,344,178		2,344,399
Other liabilities	286,196		305,092
Common stock	636		633
Treasury stock	(725,849)		(727,624)
Additional paid-in capital	1,019,061		998,728
Retained earnings	1,982,051		1,821,133
Total Steel Dynamics, Inc. equity	2,275,899		2,092,870
Total equity	2,275,899		2,092,870
Total liabilities and equity	5,190,248		5,000,659
Guarantors
Condensed Consolidating Financial Statements
Cash and equivalents	9,170		10,628	5,389		6,363
Accounts receivable, net	781,506		614,412
Inventories	523,362		487,298
Other current assets	7,979		9,757
Total current assets	1,322,017		1,122,095
Property, plant and equipment, net	668,009		684,118
Intangible assets, net	469,719		489,240
Goodwill	748,383		751,675
Other assets, including investments in subsidiaries	36,405		36,617
Total assets	3,244,533		3,083,745
Accounts payable	313,747		227,823
Accrued expenses	91,125		102,114
Current maturities of long-term debt	300		325
Total current liabilities	405,172		330,262
Other liabilities	2,179,199		2,158,725
Common stock	33,896		33,901
Additional paid-in capital	117,737		117,737
Retained earnings	508,529		443,120
Total Steel Dynamics, Inc. equity	660,162		594,758
Total equity	660,162		594,758
Total liabilities and equity	3,244,533		3,083,745
Combined Non-Guarantors
Condensed Consolidating Financial Statements
Cash and equivalents	4,400		2,322	5,373		2,215
Accounts receivable, net	13,116		7,282
Inventories	73,151		84,183
Other current assets	2,352		3,444
Total current assets	93,019		97,231
Property, plant and equipment, net	429,255		421,897
Other assets, including investments in subsidiaries	8,095		7,601
Total assets	530,369		526,729
Accounts payable	32,369		26,015
Accrued expenses	8,966		8,497
Current maturities of long-term debt	36,002		34,604
Total current liabilities	77,337		69,116
Long-term debt	187,123		168,278
Other liabilities	29,228		27,072
Redeemable noncontrolling interest	54,294		54,294
Common stock	16,121		16,121
Additional paid-in capital	262,452		256,905
Retained earnings	(77,481)		(49,022)
Total Steel Dynamics, Inc. equity	201,092		224,004
Noncontrolling interests	(18,705)		(16,035)
Total equity	182,387		207,969
Total liabilities and equity	530,369		526,729
Consolidating Adjustments
Condensed Consolidating Financial Statements
Accounts receivable, net	(300,804)		(283,388)
Inventories	(5,842)		(6,144)
Other current assets	(33,324)		(32,003)
Total current assets	(339,970)		(321,535)
Property, plant and equipment, net	(2,930)		(3,032)
Other assets, including investments in subsidiaries	(2,721,797)		(2,696,632)
Total assets	(3,064,697)		(3,021,199)
Accounts payable	(37,311)		(32,483)
Accrued expenses	(23,145)		(30,317)
Current maturities of long-term debt	(35,182)		(33,559)
Total current liabilities	(95,638)		(96,359)
Long-term debt	(153,508)		(134,780)
Other liabilities	(1,954,297)		(1,971,298)
Common stock	(50,017)		(50,022)
Additional paid-in capital	(380,189)		(374,642)
Retained earnings	(431,048)		(394,098)
Total Steel Dynamics, Inc. equity	(861,254)		(818,762)
Total equity	(861,254)		(818,762)
Total liabilities and equity	$ (3,064,697)		$ (3,021,199)