Acquisition (Details) - Severstal Columbus LLC $ in Thousands		6 Months Ended
	Sep. 16, 2014 USD ($) MT	Jun. 30, 2014 USD ($)
Business Acquisition Information
Business acquisition percentage	100.00%
Purchase price	$ 1,625,000
Working capital adjustments	$ 44,400
Additional production capacity due to acquisition (in million tons) | MT	3.4
Unaudited pro forma results
Net sales		$ 4,985,410
Net Income attributable to Steel Dynamics, Inc.		$ 161,119
Senior Notes
Business Acquisition Information
Issuance of Senior Notes	$ 1,200,000