Summary of Activity within Stockholders Equity Attributable to Real Industry and Noncontrolling Interest (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Class Of Stock [Line Items]
Balance, December 31, 2015			$ 142.4
Net earnings (loss)	$ (1.2)	$ (10.8)	(11.2)	$ (4.3)
Dividends and accretion of fair value adjustment to Redeemable Preferred Stock			(1.4)
Share-based compensation expense			1.0
Warrants exercised			0.2
Change in accumulated other comprehensive income (loss)			1.2
Balance, June 30, 2016	132.2		132.2
Equity Attributable to Real Industry, Inc.
Class Of Stock [Line Items]
Balance, December 31, 2015			141.6
Net earnings (loss)			(11.6)
Dividends and accretion of fair value adjustment to Redeemable Preferred Stock			(1.4)
Share-based compensation expense			1.0
Warrants exercised			0.2
Change in accumulated other comprehensive income (loss)			1.2
Balance, June 30, 2016	131.0		131.0
Noncontrolling Interest
Class Of Stock [Line Items]
Balance, December 31, 2015			0.8
Net earnings (loss)			0.4
Balance, June 30, 2016	$ 1.2		$ 1.2