Contingencies and Legacy Environmental Commitments - Schedule of Environmental Activity (Detail) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Mar. 31, 2015
Environmental Remediation Obligations [Abstract]
Environmental activity, Beginning balance	$ 9,255
Environmental costs incurred	(307)	$ (383)	$ (946)
Interest accretion	138	$ 149
Reduction of environmental reserve-Placerita, California	(430)
Change in estimate for pre-existing sites	430
Environmental activity, Ending balance	$ 9,086		$ 9,255