Computation of Basic and Diluted loss Per Share (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Earnings Per Share [Abstract]
Loss from continuing operations	$ (11.3)	$ (10.0)
Earnings (loss) from discontinued operations, net of income taxes	0.0	0.0
Net loss	(11.3)	(10.0)	$ (102.6)
Earnings from continuing operations attributable to noncontrolling interest	0.1	0.1
Net loss attributable to Real Industry, Inc.	(11.4)	(10.1)
Dividends on Redeemable Preferred Stock, in-kind	0.0	(0.5)	(2.0)
Dividends on Redeemable Preferred Stock, accrued	(0.6)	0.0
Accretion of fair value adjustment to Redeemable Preferred Stock	(0.2)	(0.2)	$ (1.0)
Net loss available to common stockholders	$ (12.2)	$ (10.8)
Denominator for basic and diluted loss per share—Weighted average shares outstanding	28,872,312	28,703,587
Basic and diluted loss per share:
Continuing operations	$ (0.43)	$ (0.38)
Discontinued operations	0	0
Basic and diluted loss per share	$ (0.43)	$ (0.38)