Condensed Consolidating Information (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012
Condensed Consolidating Balance Sheets
Ownership interest in subsidiaries (as a percent)	100.00%
Cash and equivalents	$ 357,490	$ 342,919	$ 395,156	$ 243,753	$ 477,861	$ 375,917
Accounts receivable, net	910,796		720,600
Inventories	1,320,871		1,314,747
Other current assets	41,029		43,131
Total current assets	2,630,186		2,473,634
Property, plant and equipment, net	2,177,007		2,226,134
Intangible assets, net	372,819		386,159
Goodwill	728,751		731,996
Other assets, including investments in subs	76,439		115,083
Total assets	5,985,202		5,933,006	5,735,910
Accounts payable	440,691		414,932
Accrued expenses	210,771		218,702
Current maturities of long-term debt	61,761		341,544
Total current liabilities	713,223		975,178
Long-term debt	1,742,128		1,766,045
Other liabilities	570,641		579,414
Redeemable noncontrolling interests	124,180		116,514
Common stock	647		645
Treasury stock	(398,818)		(718,529)
Additional paid-in capital	1,058,921		1,085,694
Retained earnings (deficit)	2,237,147		2,179,513
Total Steel Dynamics, Inc. equity	2,897,897		2,547,323
Noncontrolling interests	(62,867)		(51,468)
Total equity	2,835,030		2,495,855
Total liabilities and equity	5,985,202		5,933,006
Reportable Legal Entities [Member] | Parent Company [Member]
Condensed Consolidating Balance Sheets
Cash and equivalents	297,225		320,866	213,717		322,707
Accounts receivable, net	367,627		309,691
Inventories	684,841		673,763
Other current assets	47,442		50,228
Total current assets	1,397,135		1,354,548
Property, plant and equipment, net	1,033,622		1,046,093
Other assets, including investments in subs	2,615,185		2,630,411
Total assets	5,045,942		5,031,052
Accounts payable	168,091		160,255
Accrued expenses	142,351		142,055
Current maturities of long-term debt	34,925		315,521
Total current liabilities	345,367		617,831
Long-term debt	1,704,528		1,725,433
Other liabilities	98,150		140,465
Common stock	647		645
Treasury stock	(398,818)		(718,529)
Additional paid-in capital	1,058,921		1,085,694
Retained earnings (deficit)	2,237,147		2,179,513
Total Steel Dynamics, Inc. equity	2,897,897		2,547,323
Total equity	2,897,897		2,547,323
Total liabilities and equity	5,045,942		5,031,052
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Condensed Consolidating Balance Sheets
Cash and equivalents	50,461		61,148	14,726		41,675
Accounts receivable, net	1,077,153		874,707
Inventories	543,977		557,640
Other current assets	7,719		8,399
Total current assets	1,679,310		1,501,894
Property, plant and equipment, net	584,587		619,617
Intangible assets, net	372,819		386,159
Goodwill	728,751		731,996
Other assets, including investments in subs	21,781		21,789
Total assets	3,387,248		3,261,455
Accounts payable	284,773		258,406
Accrued expenses	117,303		115,182
Current maturities of long-term debt	300		300
Total current liabilities	402,376		373,888
Other liabilities	2,022,395		1,986,260
Common stock	33,896		33,896
Additional paid-in capital	117,737		117,737
Retained earnings (deficit)	810,844		749,674
Total Steel Dynamics, Inc. equity	962,477		901,307
Total equity	962,477		901,307
Total liabilities and equity	3,387,248		3,261,455
Reportable Legal Entities [Member] | Non Guarantor Subsidiaries [Member]
Condensed Consolidating Balance Sheets
Cash and equivalents	9,804		13,142	15,310		11,535
Accounts receivable, net	49,880		32,018
Inventories	97,561		91,199
Other current assets	4,310		3,259
Total current assets	161,555		139,618
Property, plant and equipment, net	561,115		562,843
Other assets, including investments in subs	7,109		8,092
Total assets	729,779		710,553
Accounts payable	94,049		60,987
Accrued expenses	10,089		10,694
Current maturities of long-term debt	66,474		52,163
Total current liabilities	170,612		123,844
Long-term debt	184,554		204,385
Other liabilities	35,504		34,895
Redeemable noncontrolling interests	124,180		116,514
Common stock	18,121		18,121
Additional paid-in capital	585,348		552,946
Retained earnings (deficit)	(325,673)		(288,684)
Total Steel Dynamics, Inc. equity	277,796		282,383
Noncontrolling interests	(62,867)		(51,468)
Total equity	214,929		230,915
Total liabilities and equity	729,779		710,553
Consolidation Eliminations [Member]
Condensed Consolidating Balance Sheets
Accounts receivable, net	(583,864)		(495,816)
Inventories	(5,508)		(7,855)
Other current assets	(18,442)		(18,755)
Total current assets	(607,814)		(522,426)
Property, plant and equipment, net	(2,317)		(2,419)
Other assets, including investments in subs	(2,567,636)		(2,545,209)
Total assets	(3,177,767)		(3,070,054)
Accounts payable	(106,222)		(64,716)
Accrued expenses	(58,972)		(49,229)
Current maturities of long-term debt	(39,938)		(26,440)
Total current liabilities	(205,132)		(140,385)
Long-term debt	(146,954)		(163,773)
Other liabilities	(1,585,408)		(1,582,206)
Common stock	(52,017)		(52,017)
Additional paid-in capital	(703,085)		(670,683)
Retained earnings (deficit)	(485,171)		(460,990)
Total Steel Dynamics, Inc. equity	(1,240,273)		(1,183,690)
Total equity	(1,240,273)		(1,183,690)
Total liabilities and equity	$ (3,177,767)		$ (3,070,054)