Summary of Activity within Stockholders Equity Attributable to Real Industry and Noncontrolling Interest (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Class Of Stock [Line Items]
Balance, beginning of period	$ 142.4
Net earnings (loss)	(10.0)	$ 6.8
Dividends and accretion on Redeemable Preferred Stock	(0.7)
Share-based compensation expense	0.5
Change in accumulated other comprehensive income (loss)	2.6
Balance, end of period	134.8
Equity Attributable to Real Industry, Inc.
Class Of Stock [Line Items]
Balance, beginning of period	141.6
Net earnings (loss)	(10.1)
Dividends and accretion on Redeemable Preferred Stock	(0.7)
Share-based compensation expense	0.5
Change in accumulated other comprehensive income (loss)	2.6
Balance, end of period	133.9
Noncontrolling Interest
Class Of Stock [Line Items]
Balance, beginning of period	0.8
Net earnings (loss)	0.1
Balance, end of period	$ 0.9