Employee Benefits (Details 5) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Contributions to Company Sponsored Retirement Plans
Company's expense (credit)for Reliance-sponsored retirement plans	$ 30.5	$ 27.2	$ 25.6
Master Plan
Contributions to Company Sponsored Retirement Plans
Company's expense (credit)for Reliance-sponsored retirement plans	19.0	16.9	14.8
Other Defined Contribution Plans
Contributions to Company Sponsored Retirement Plans
Company's expense (credit)for Reliance-sponsored retirement plans	4.8	3.9	2.4
Employee Stock Ownership Plan
Contributions to Company Sponsored Retirement Plans
Company's expense (credit)for Reliance-sponsored retirement plans	1.4	1.4	1.2
Deferred Compensation Plan
Contributions to Company Sponsored Retirement Plans
Company's expense (credit)for Reliance-sponsored retirement plans	0.5	0.5	1.0
Supplemental Executive Retirement Plans
Contributions to Company Sponsored Retirement Plans
Company's expense (credit)for Reliance-sponsored retirement plans	2.9	2.0	3.1
Defined Benefit Plans
Contributions to Company Sponsored Retirement Plans
Company's expense (credit)for Reliance-sponsored retirement plans	2.4	0.7	1.0
Postretirement Medical Plans
Contributions to Company Sponsored Retirement Plans
Company's expense (credit)for Reliance-sponsored retirement plans	$ (0.5)	$ 1.8	$ 2.1

The amount of pension and other (such as medical, dental and life insurance) postretirement benefit costs recognized during the period for (1) defined benefit plans (periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss) on assets, prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments) and for (2) defined contribution plans (to the extent that a plan's defined contributions to an individual's account are to be made for periods in which that individual renders services, the net cost for a period is the contribution called for in that period; if a plan calls for contributions for periods after an individual retires or terminates, the estimated cost is accrued during the employee's service period).

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-Name Accounting Standards Codification

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details