Employee Retirement Benefit Plans - Components of Company's Net Periodic Benefit Costs (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Jun. 30, 2016
Components of net periodic benefit cost:
Service cost		$ 0.8	$ 0.7	$ 1.6	$ 1.4
Interest cost		1.6	2.7	3.3	5.4
Expected return on plan assets		(2.6)	(2.5)	(5.4)	(5.1)
Amortization	[1]	1.0	0.7	2.1	1.4
Net amount recognized		0.8	$ 1.6	1.6	$ 3.1
Estimated discounted value of future employer contributions		39.1		39.1		$ 39.3
Estimated annual cash contribution		$ 1.7		$ 1.7

[1] Amount represents the amortization of unrecognized actuarial gains/(losses).