CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Net sales
Unrelated parties	$ 2,399,116	$ 2,060,596	$ 7,066,083	$ 5,737,584
Related parties	44,266	40,714	136,235	128,929
Total net sales	2,443,382	2,101,310	7,202,318	5,866,513
Costs of goods sold	2,046,864	1,692,807	5,941,128	4,841,591
Gross profit	396,518	408,503	1,261,190	1,024,922
Selling, general and administrative expenses	97,056	95,185	298,422	279,899
Profit sharing	21,175	22,255	69,714	51,722
Amortization of intangible assets	7,272	7,208	22,120	21,359
Operating income	271,015	283,855	870,934	671,942
Interest expense, net of capitalized interest	34,177	36,199	102,019	109,888
Other expense (income), net	2,526	4,351	(4,968)	741
Income before income taxes	234,312	243,305	773,883	561,313
Income tax expense	83,300	88,892	271,258	205,139
Net income	151,012	154,413	502,625	356,174
Net loss attributable to noncontrolling interests	2,246	2,984	5,383	5,929
Net income attributable to Steel Dynamics, Inc.	$ 153,258	$ 157,397	$ 508,008	$ 362,103
Basic earnings per share attributable to Steel Dynamics, Inc. stockholders	$ 0.64	$ 0.65	$ 2.11	$ 1.49
Weighted average common shares outstanding - basic (in shares)	239,066	243,761	241,117	243,539
Diluted earnings per share attributable to Steel Dynamics, Inc. stockholders, including the effect of assumed conversions when dilutive (in dollars per share)	$ 0.64	$ 0.64	$ 2.09	$ 1.48
Weighted average common shares and share equivalents outstanding (in shares)	240,880	245,682	242,816	245,227
Dividends declared per share (in dollars per share)	$ 0.155	$ 0.140	$ 0.465	$ 0.420