Long-Term Debt - Foreign Debt - Additional Information (Detail) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Foreign debt	$ 13.7	$ 19.5
Foreign Debt [Member]
Debt Instrument [Line Items]
Available credit facility	32.0	26.0
Letters of credit issued by our foreign subsidiaries	3.0	3.0
Foreign Debt [Member] | Owed to Banks [Member] | Ryerson China [Member]
Debt Instrument [Line Items]
Foreign debt	$ 13.7	$ 19.5
Weighted average interest rate	4.30%	4.30%