CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net sales
Unrelated parties	$ 10,451,132	$ 11,801,609	$ 9,364,213
Related parties	13,859	20,230	174,584
Total net sales	10,464,991	11,821,839	9,538,797
Costs of goods sold	8,934,007	9,499,025	7,956,783
Gross profit	1,530,984	2,322,814	1,582,014
Selling, general and administrative expenses	436,498	416,640	394,631
Profit sharing	78,029	155,985	91,309
Amortization of intangible assets	29,577	27,780	29,193
Operating income	986,880	1,722,409	1,066,881
Interest expense, net of capitalized interest	127,104	126,620	134,399
Other income, net	(15,561)	(23,985)	(2,753)
Income before income taxes	875,337	1,619,774	935,235
Income tax expense	197,437	363,969	129,439
Net income	677,900	1,255,805	805,796
Net (income) loss attributable to noncontrolling interests	(6,797)	2,574	6,945
Net income attributable to Steel Dynamics, Inc.	$ 671,103	$ 1,258,379	$ 812,741
Basic earnings per share attributable to Steel Dynamics, Inc. stockholders	$ 3.06	$ 5.38	$ 3.38
Weighted average common shares outstanding (in shares)	219,639	233,923	240,132
Diluted earnings per share attributable to Steel Dynamics, Inc. stockholders, including the effect of assumed conversions when dilutive (in dollars per share)	$ 3.04	$ 5.35	$ 3.36
Weighted average common shares and share equivalents outstanding (in shares)	220,748	235,193	241,781
Dividends declared per share (in dollars per share)	$ 0.96	$ 0.75	$ 0.62