Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Numerator:
Net income attributable to Reliance	$ 92.2	$ 101.3
Denominator for basic earnings per share:
Weighted average shares outstanding (in shares)	71,929,821	77,119,266
Effect of dilutive securities:
Dilutive effect of stock-based awards (in shares)	778,528	713,054
Denominator:
Weighted average diluted shares outstanding (in shares)	72,708,349	77,832,320
Net income per share attributable to Reliance shareholders - diluted (in dollars per share)	$ 1.27	$ 1.30
Net income per share attributable to Reliance shareholders - basic (in dollars per share)	$ 1.28	$ 1.31