CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net sales
Unrelated parties	$ 11,801,609	$ 9,364,213	$ 7,607,180
Related parties	20,230	174,584	169,929
Total net sales	11,821,839	9,538,797	7,777,109
Costs of goods sold	9,499,025	7,956,783	6,442,245
Gross profit	2,322,814	1,582,014	1,334,864
Selling, general and administrative expenses	416,640	394,631	374,009
Profit sharing	155,985	91,309	71,285
Amortization of intangible assets	27,780	29,193	28,765
Asset impairment charge			132,839
Operating income	1,722,409	1,066,881	727,966
Interest expense, net of capitalized interest	126,620	134,399	146,037
Other expense (income), net	(23,985)	(2,753)	17,796
Income before income taxes	1,619,774	935,235	564,133
Income tax expense	363,969	129,439	204,127
Net income	1,255,805	805,796	360,006
Net loss attributable to noncontrolling interests	2,574	6,945	22,109
Net income attributable to Steel Dynamics, Inc.	$ 1,258,379	$ 812,741	$ 382,115
Basic earnings per share attributable to Steel Dynamics, Inc. stockholders	$ 5.38	$ 3.38	$ 1.57
Weighted average common shares outstanding (in shares)	233,923	240,132	243,576
Diluted earnings per share attributable to Steel Dynamics, Inc. stockholders, including the effect of assumed conversions when dilutive (in dollars per share)	$ 5.35	$ 3.36	$ 1.56
Weighted average common shares and share equivalents outstanding (in shares)	235,193	241,781	245,298
Dividends declared per share (in dollars per share)	$ 0.75	$ 0.62	$ 0.56