Computation of Basic and Diluted Earnings (loss) Per Share (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Earnings (loss) from continuing operations	$ 2.0	$ (0.7)	$ (29.5)	$ (4.2)
Earnings (loss) from discontinued operations, net of income taxes	(0.7)	1.5	26.5	4.6
Net earnings (loss)	1.3	0.8	(3.0)	0.4
Earnings from continuing operations attributable to noncontrolling interest	0.1		0.3
Net earnings (loss) attributable to Real Industry, Inc.	1.2	0.8	(3.3)	0.4
Dividends and accretion on Redeemable Preferred Stock	(0.7)		(1.6)
Numerator for basic and diluted earnings per share—Net earnings (loss) available to common stockholders	$ 0.5	$ 0.8	$ (4.9)	$ 0.4
Denominator for basic earnings per share— Weighted average shares outstanding	28,556,383	13,162,987	25,993,660	13,151,059
Effect of dilutive securities
Denominator for diluted earnings per share— Weighted average shares outstanding	29,813,473	13,162,987	25,993,660	13,151,059
Continuing operations	$ 0.04	$ (0.05)	$ (1.21)	$ (0.32)
Discontinued operations	(0.02)	0.11	1.02	0.35
Basic earnings (loss) per share	0.02	0.06	(0.19)	0.03
Continuing operations	0.04	(0.05)	(1.21)	(0.32)
Discontinued operations	(0.02)	0.11	1.02	0.35
Diluted earnings (loss) per share	$ 0.02	$ 0.06	$ (0.19)	$ 0.03