Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator:
Net income attributable to Reliance (in dollars)	$ 51.4	$ 95.5	$ 242.9	$ 279.2
Denominator:
Weighted average shares outstanding	73,316,356	77,945,375	74,903,472	77,730,965
Dilutive effect of stock-based awards	819,837	938,806	770,124	943,894
Weighted average diluted shares outstanding	74,136,193	78,884,181	75,673,596	78,674,859
Diluted earnings per common share (in dollars per share)	$ 0.69	$ 1.21	$ 3.21	$ 3.55
Basic earnings per common share (in dollars per share)	$ 0.70	$ 1.23	$ 3.24	$ 3.59