Acquisitions - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2018
Fanello Industries [Member]
Business Acquisition [Line Items]
Effective date of acquisition	Apr. 02, 2018
Description of business acquisition	On April 2, 2018, Ryerson Holding acquired Fanello Industries, LLC (“Fanello”), a privately owned metal service company located in Lavonia, Georgia.
The Laserflex Corporation [Member]
Business Acquisition [Line Items]
Effective date of acquisition	Jan. 19, 2017
Description of business acquisition	On January 19, 2017, Ryerson Holding acquired The Laserflex Corporation (“Laserflex”), a privately-owned metal fabricator specializing in laser fabrication metal processing and welding with locations in Columbus, Ohio and Wellford, South Carolina.
Guy Metals, Inc [Member]
Business Acquisition [Line Items]
Effective date of acquisition	Feb. 15, 2017
Description of business acquisition	On February 15, 2017, Ryerson Holding acquired Guy Metals, Inc. (“Guy Metals”), a privately-owned metal service center company located in Hammond, Wisconsin.