Earnings Per Share (Details) - Entity [Domain] - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Numerator:
Net income attributable to Reliance (in dollars)	$ 90.2	$ 96.5	$ 191.5	$ 183.7
Denominator:
Weighted average shares outstanding	74,316,582	77,735,301	75,710,182	77,621,983
Dilutive effect of stock-based awards	777,480	1,042,451	745,267	946,439
Weighted average diluted shares outstanding	75,094,062	78,777,752	76,455,449	78,568,422
Diluted earnings per common share (in dollars per share)	$ 1.20	$ 1.22	$ 2.50	$ 2.34
Basic earnings per common share (in dollars per share)	$ 1.21	$ 1.24	$ 2.53	$ 2.37
Diluted shares
Weighted average shares, respectively, primarily for RSU's and stock options, not included in the diluted calculation due to their aniti-dilutive effect	39,834	46,255	123,617	31,940