CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net sales
Unrelated parties	$ 8,481,567	$ 7,087,101	$ 7,007,417
Related parties	274,385	285,823	282,817
Total net sales	8,755,952	7,372,924	7,290,234
Costs of goods sold	7,789,741	6,653,780	6,570,336
Gross profit	966,211	719,144	719,898
Selling, general and administrative expenses	316,214	272,777	257,943
Profit sharing	42,126	27,764	26,987
Amortization of intangible assets	27,551	31,770	35,553
Impairment charges	260,000	308	8,250
Operating income	320,320	386,525	391,165
Interest expense, net of capitalized interest	137,263	127,728	158,585
Other (income) expense, net	18,254	(4,033)	28,514
Income before income taxes	164,803	262,830	204,066
Income taxes	73,153	99,314	61,785
Net income	91,650	163,516	142,281
Net loss attributable to noncontrolling interests	65,374	25,798	21,270
Net income attributable to Steel Dynamics, Inc.	$ 157,024	$ 189,314	$ 163,551
Basic earnings per share attributable to Steel Dynamics, Inc. stockholders (in dollars per share)	$ 0.68	$ 0.86	$ 0.75
Weighted average common shares outstanding (in shares)	232,547	220,916	219,159
Diluted earnings per share attributable to Steel Dynamics, Inc. stockholders, including the effect of assumed conversions when dilutive (in dollars per share)	$ 0.67	$ 0.83	$ 0.73
Weighted average common shares and share equivalents outstanding (in shares)	242,078	238,996	236,624
Dividends declared per share (in dollars per share)	$ 0.46	$ 0.44	$ 0.40