Earnings Per Share (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Numerator:
Net income attributable to Reliance (in dollars)	$ 81.0	$ 108.8	$ 164.7	$ 225.0
Denominator for basic earnings per share:
Weighted average shares	76,695,598	75,087,057	76,497,454	75,004,840
Effect of dilutive securities:
Stock options and restricted shares (in shares)	773,519	424,192	778,557	464,129
Denominator for diluted earnings per share:
Adjusted weighted average shares and assumed conversions	77,469,117	75,511,249	77,276,011	75,468,969
Net income per share attributable to Reliance shareholders - diluted (in dollars per share)	$ 1.05	$ 1.44	$ 2.13	$ 2.98
Net income per share attributable to Reliance shareholders - basic (in dollars per share)	$ 1.06	$ 1.45	$ 2.15	$ 3.00
Diluted shares
Shares reserved for issuance upon exercise of outstanding stock options or vesting of restricted shares respectively, not included in the diluted calculation due to their anti-dilutive effect	144,143	2,462,550	313,912	2,468,973