Schedule of Activity Associated with Goodwill (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)
Goodwill And Other Intangible Assets [Line Items]
Acquisition of Real Alloy	$ 104.6
Currency translation adjustments	(0.3)
Balance at end of period	104.3
RANA
Goodwill And Other Intangible Assets [Line Items]
Acquisition of Real Alloy	95.4
Balance at end of period	95.4
RAEU
Goodwill And Other Intangible Assets [Line Items]
Acquisition of Real Alloy	9.2
Currency translation adjustments	(0.3)
Balance at end of period	$ 8.9