Computation of Basic and Diluted loss Per Share (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Loss from continuing operations	$ (6.2)	$ (1.3)	$ (17.5)	$ (11.3)
Earnings from discontinued operations, net of income taxes	0.0	0.1	0.0	0.1
Net loss	(6.2)	(1.2)	(17.5)	(11.2)
Earnings from continuing operations attributable to noncontrolling interest	0.3	0.3	0.4	0.4
Net loss attributable to Real Industry, Inc.	(6.5)	(1.5)	(17.9)	(11.6)
Dividends on Redeemable Preferred Stock, in-kind	0.0	(0.5)	0.0	(0.9)
Dividends on Redeemable Preferred Stock, in cash or accrued	(0.5)	0.0	(1.1)	0.0
Accretion of fair value adjustment to Redeemable Preferred Stock	(0.3)	(0.2)	(0.5)	(0.5)
Net loss available to common stockholders	$ (7.3)	$ (2.2)	$ (19.5)	$ (13.0)
Denominator for basic and diluted loss per share—Weighted average shares outstanding	29,009,854	29,252,343	28,914,533	29,160,245
Basic and diluted loss per share:
Continuing operations	$ (0.25)	$ (0.08)	$ (0.67)	$ (0.43)
Discontinued operations	0	0.01	0	0
Basic and diluted loss per share	$ (0.25)	$ (0.07)	$ (0.67)	$ (0.43)