Computation of Basic and Diluted Earnings (loss) Per Share (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Loss from continuing operations									$ (31.7)	$ (0.1)	$ (14.2)
Earnings from discontinued operations, net of income taxes									24.9	5.5	4.2
Net earnings (loss)									(6.8)	5.4	(10.0)
Earnings (loss) from continuing operations attributable to noncontrolling interest									0.1	(0.1)
Net earnings (loss) attributable to Real Industry, Inc.	$ (3.9)	$ 1.2	$ (10.9)	$ 6.7	$ 5.1	$ 0.8	$ (0.5)	$ 0.1	(6.9)	5.5	(10.0)
Dividends and accretion on Redeemable Preferred Stock									(2.3)
Net earnings (loss) available to common stockholders									$ (9.2)	$ 5.5	$ (10.0)
Denominator for basic and diluted earnings (loss) per share— Weighted average shares outstanding									26,657,832	13,403,083	12,836,071
Basic and diluted earnings (loss) per share:
Continuing operations									$ (1.28)		$ (1.11)
Discontinued operations									0.93	$ 0.41	0.32
Basic and diluted earnings (loss) per share									$ (0.35)	$ 0.41	$ (0.79)