Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	12 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2015
Compensation And Retirement Disclosure [Abstract]
Service cost		$ 0.6	$ 1.3
Interest cost	$ 0.7	0.7	0.7
Expected return on plan assets	(1.0)	(0.9)	(0.9)
Amortization of net actuarial loss recognized		0.1	0.2
Total net periodic benefit cost	$ (0.3)	$ 0.5	$ 1.3