Condensed Consolidating Information (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Condensed Consolidating Balance Sheets
Ownership interest in subsidiaries (as a percent)	100.00%
Cash and equivalents	$ 342,919	$ 395,156	$ 477,861	$ 375,917
Accounts receivable, net	811,100	720,600
Inventories	1,332,101	1,314,747
Other current assets	42,234	43,131
Total current assets	2,528,354	2,473,634
Property, plant and equipment, net	2,197,503	2,226,134
Intangible assets, net	379,488	386,159
Goodwill	730,360	731,996
Other assets, including investments in subs	78,152	115,083
Total assets	5,913,857	5,933,006	5,956,574
Accounts payable	417,168	414,932
Accrued expenses	190,541	218,702
Current maturities of long-term debt	343,722	341,544
Total current liabilities	951,431	975,178
Long-term debt	1,755,028	1,766,045
Other liabilities	573,068	579,414
Redeemable noncontrolling interests	121,834	116,514
Common stock	646	645
Treasury stock	(716,545)	(718,529)
Additional paid-in capital	1,092,281	1,085,694
Retained earnings (deficit)	2,192,413	2,179,513
Total Steel Dynamics, Inc. equity	2,568,795	2,547,323
Noncontrolling interests	(56,299)	(51,468)
Total equity	2,512,496	2,495,855
Total liabilities and equity	5,913,857	5,933,006
Reportable legal entity | Parent
Condensed Consolidating Balance Sheets
Cash and equivalents	281,376	320,866	441,989	322,707
Accounts receivable, net	320,996	309,691
Inventories	728,638	673,763
Other current assets	48,969	50,228
Total current assets	1,379,979	1,354,548
Property, plant and equipment, net	1,042,424	1,046,093
Other assets, including investments in subs	2,604,100	2,630,411
Total assets	5,026,503	5,031,052
Accounts payable	178,731	160,255
Accrued expenses	124,762	142,055
Current maturities of long-term debt	318,969	315,521
Total current liabilities	622,462	617,831
Long-term debt	1,714,982	1,725,433
Other liabilities	120,264	140,465
Common stock	646	645
Treasury stock	(716,545)	(718,529)
Additional paid-in capital	1,092,281	1,085,694
Retained earnings (deficit)	2,192,413	2,179,513
Total Steel Dynamics, Inc. equity	2,568,795	2,547,323
Total equity	2,568,795	2,547,323
Total liabilities and equity	5,026,503	5,031,052
Reportable legal entity | Guarantors
Condensed Consolidating Balance Sheets
Cash and equivalents	48,071	61,148	22,546	41,675
Accounts receivable, net	1,012,562	874,707
Inventories	502,339	557,640
Other current assets	6,968	8,399
Total current assets	1,569,940	1,501,894
Property, plant and equipment, net	598,946	619,617
Intangible assets, net	379,488	386,159
Goodwill	730,360	731,996
Other assets, including investments in subs	21,572	21,789
Total assets	3,300,306	3,261,455
Accounts payable	266,205	258,406
Accrued expenses	107,284	115,182
Current maturities of long-term debt	300	300
Total current liabilities	373,789	373,888
Other liabilities	2,004,584	1,986,260
Common stock	33,896	33,896
Additional paid-in capital	117,737	117,737
Retained earnings (deficit)	770,300	749,674
Total Steel Dynamics, Inc. equity	921,933	901,307
Total equity	921,933	901,307
Total liabilities and equity	3,300,306	3,261,455
Reportable legal entity | Combined Non-Guarantors
Condensed Consolidating Balance Sheets
Cash and equivalents	13,472	13,142	13,326	11,535
Accounts receivable, net	42,095	32,018
Inventories	105,553	91,199
Other current assets	5,048	3,259
Total current assets	166,168	139,618
Property, plant and equipment, net	558,500	562,843
Other assets, including investments in subs	7,352	8,092
Total assets	732,020	710,553
Accounts payable	89,012	60,987
Accrued expenses	10,050	10,694
Current maturities of long-term debt	66,580	52,163
Total current liabilities	165,642	123,844
Long-term debt	182,506	204,385
Other liabilities	30,844	34,895
Redeemable noncontrolling interests	121,834	116,514
Common stock	18,121	18,121
Additional paid-in capital	575,877	552,946
Retained earnings (deficit)	(306,505)	(288,684)
Total Steel Dynamics, Inc. equity	287,493	282,383
Noncontrolling interests	(56,299)	(51,468)
Total equity	231,194	230,915
Total liabilities and equity	732,020	710,553
Consolidating Adjustments
Condensed Consolidating Balance Sheets
Accounts receivable, net	(564,553)	(495,816)
Inventories	(4,429)	(7,855)
Other current assets	(18,751)	(18,755)
Total current assets	(587,733)	(522,426)
Property, plant and equipment, net	(2,367)	(2,419)
Other assets, including investments in subs	(2,554,872)	(2,545,209)
Total assets	(3,144,972)	(3,070,054)
Accounts payable	(116,780)	(64,716)
Accrued expenses	(51,555)	(49,229)
Current maturities of long-term debt	(42,127)	(26,440)
Total current liabilities	(210,462)	(140,385)
Long-term debt	(142,460)	(163,773)
Other liabilities	(1,582,624)	(1,582,206)
Common stock	(52,017)	(52,017)
Additional paid-in capital	(693,614)	(670,683)
Retained earnings (deficit)	(463,795)	(460,990)
Total Steel Dynamics, Inc. equity	(1,209,426)	(1,183,690)
Total equity	(1,209,426)	(1,183,690)
Total liabilities and equity	$ (3,144,972)	$ (3,070,054)