Employee Benefits - Additional (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Contributions to Company Sponsored Retirement Plans
Company's expense for Reliance-sponsored retirement plans	$ 47.0	$ 45.6	$ 43.0
Master 401(k) Plan
Contributions to Company Sponsored Retirement Plans
Company's expense for Reliance-sponsored retirement plans	29.3	28.1	25.6
Precision Strip Retirement and Savings Plan
Contributions to Company Sponsored Retirement Plans
Company's expense for Reliance-sponsored retirement plans	10.9	9.2	8.0
Supplemental Executive Retirement Plans
Contributions to Company Sponsored Retirement Plans
Company's expense for Reliance-sponsored retirement plans	1.2	4.0	3.4
Deferred Compensation Plan
Contributions to Company Sponsored Retirement Plans
Company's expense for Reliance-sponsored retirement plans	2.4	2.0	2.5
Other Defined Contribution Plans
Contributions to Company Sponsored Retirement Plans
Company's expense for Reliance-sponsored retirement plans	2.0	2.0	2.0
Defined Benefit Plan
Contributions to Company Sponsored Retirement Plans
Company's expense for Reliance-sponsored retirement plans	$ 1.2	$ 0.3	$ 1.5