Summary of Activity within Stockholders Equity and Noncontrolling Interest (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Class Of Stock [Line Items]
Balance at beginning of period			$ 85.6
Net earnings (loss)	$ 1.3	$ 0.8	(3.0)	$ 0.4
Dividends and accretion on Redeemable Preferred Stock	(0.7)		(1.6)
Exercise of common stock options			1.1
Issuance of common stock, net of issuance costs			63.3
Share-based compensation expense			1.0	$ 1.0
Proceeds from Warrant exercises			0.1
Reclassification of common stock warrant liability on Warrant exercises			0.2
Treasury shares acquired, net of reissuances			(0.1)
Noncontrolling interest acquired in business combination			0.8
Change in accumulated other comprehensive loss			(2.6)
Balance at end of period	144.8		144.8
Equity Attributable to Real Industry, Inc.
Class Of Stock [Line Items]
Balance at beginning of period			85.7
Net earnings (loss)			(3.3)
Dividends and accretion on Redeemable Preferred Stock			(1.6)
Exercise of common stock options			1.1
Issuance of common stock, net of issuance costs			63.3
Share-based compensation expense			1.0
Proceeds from Warrant exercises			0.1
Reclassification of common stock warrant liability on Warrant exercises			0.2
Treasury shares acquired, net of reissuances			(0.1)
Change in accumulated other comprehensive loss			(2.6)
Balance at end of period	143.8		143.8
Noncontrolling Interest
Class Of Stock [Line Items]
Balance at beginning of period			(0.1)
Net earnings (loss)			0.3
Noncontrolling interest acquired in business combination			0.8
Balance at end of period	$ 1.0		$ 1.0