Employee Benefits - Supplemental Bonus Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Contributions to Company Sponsored Retirement Plans
Company's expense for Reliance-sponsored retirement plans	$ 45.6	$ 43.0	$ 53.0
Master 401(k) Plan
Contributions to Company Sponsored Retirement Plans
Company's expense for Reliance-sponsored retirement plans	28.1	25.6	21.2
Precision Strip Retirement and Savings Plan
Contributions to Company Sponsored Retirement Plans
Company's expense for Reliance-sponsored retirement plans	9.2	8.0	5.2
Supplemental Executive Retirement Plans
Contributions to Company Sponsored Retirement Plans
Company's expense for Reliance-sponsored retirement plans	4.0	3.4	10.5
Deferred Compensation Plan
Contributions to Company Sponsored Retirement Plans
Company's expense for Reliance-sponsored retirement plans	2.0	2.5	(0.3)
Other Defined Contribution Plans
Contributions to Company Sponsored Retirement Plans
Company's expense for Reliance-sponsored retirement plans	2.0	2.0	1.7
Defined Benefit Plans
Contributions to Company Sponsored Retirement Plans
Company's expense for Reliance-sponsored retirement plans	$ 0.3	$ 1.5	$ 14.7