Condensed Consolidating Information (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Condensed Consolidating Statements of Operations
Net sales	$ 1,830,082	$ 1,795,696
Costs of goods sold	1,666,778	1,619,432
Gross profit	163,304	176,264
Selling, general and administrative	82,372	80,032
Operating income	80,932	96,232
Interest expense, net of capitalized interest	30,569	34,629
Other (income) expense, net	(631)	(1,046)
Income before income taxes	50,994	62,649
Income taxes (benefit)	17,296	21,397
Net income	33,698	41,252
Net loss attributable to noncontrolling interests	4,881	6,963
Net income attributable to Steel Dynamics, Inc.	38,579	48,215
Reportable legal entity | Parent
Condensed Consolidating Statements of Operations
Net sales	863,563	827,201
Costs of goods sold	761,395	706,387
Gross profit	102,168	120,814
Selling, general and administrative	28,834	28,686
Operating income	73,334	92,128
Interest expense, net of capitalized interest	19,361	22,046
Other (income) expense, net	(976)	(820)
Income before income taxes	54,949	70,902
Income taxes (benefit)	9,925	11,394
Net income	45,024	59,508
Equity in net loss of subsidiaries	(6,445)	(11,293)
Net income attributable to Steel Dynamics, Inc.	38,579	48,215
Reportable legal entity | Guarantors
Condensed Consolidating Statements of Operations
Net sales	2,112,389	2,015,487
Costs of goods sold	2,015,576	1,914,058
Gross profit	96,813	101,429
Selling, general and administrative	54,289	53,992
Operating income	42,524	47,437
Interest expense, net of capitalized interest	10,561	12,039
Other (income) expense, net	395	(200)
Income before income taxes	31,568	35,598
Income taxes (benefit)	10,942	12,919
Net income	20,626	22,679
Net income attributable to Steel Dynamics, Inc.	20,626	22,679
Reportable legal entity | Combined Non-Guarantors
Condensed Consolidating Statements of Operations
Net sales	105,849	66,370
Costs of goods sold	123,573	95,941
Gross profit	(17,724)	(29,571)
Selling, general and administrative	3,408	2,138
Operating income	(21,132)	(31,709)
Interest expense, net of capitalized interest	1,880	1,701
Other (income) expense, net	(1,284)	(1,183)
Income before income taxes	(21,728)	(32,227)
Income taxes (benefit)	696	699
Net income	(22,424)	(32,926)
Net loss attributable to noncontrolling interests	4,881	6,963
Net income attributable to Steel Dynamics, Inc.	(17,543)	(25,963)
Consolidating Adjustments
Condensed Consolidating Statements of Operations
Net sales	(1,251,719)	(1,113,362)
Costs of goods sold	(1,233,766)	(1,096,954)
Gross profit	(17,953)	(16,408)
Selling, general and administrative	(4,159)	(4,784)
Operating income	(13,794)	(11,624)
Interest expense, net of capitalized interest	(1,233)	(1,157)
Other (income) expense, net	1,234	1,157
Income before income taxes	(13,795)	(11,624)
Income taxes (benefit)	(4,267)	(3,615)
Net income	(9,528)	(8,009)
Equity in net loss of subsidiaries	6,445	11,293
Net income attributable to Steel Dynamics, Inc.	$ (3,083)	$ 3,284