Earnings Per Share (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Numerator:
Net income attributable to Reliance (in dollars)	$ 83.7	$ 116.2
Denominator for basic earnings per share:
Weighted average shares	76,297,108	74,922,487
Effect of dilutive securities:
Stock options and restricted shares	783,595	504,065
Denominator for diluted earnings per share:
Adjusted weighted average shares and assumed conversions	77,080,703	75,426,552
Net income per share attributable to Reliance shareholders - diluted (in dollars per share)	$ 1.09	$ 1.54
Net income per share attributable to Reliance shareholders - basic (in dollars per share)	$ 1.10	$ 1.55
Diluted shares
Shares reserved for issuance upon exercise of stock options or vesting of restricted shares respectively, not included in the diluted calculation due to their anti-dilutive effect	483,680	2,475,395