Pension and Post-Retirement Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended		3 Months Ended		6 Months Ended
	Jan. 31, 2018	Apr. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Compensation And Retirement Disclosure [Abstract]
Cash contribution to pension plan during the period	$ 10.0	$ 10.0
Pension plan liabilities			$ 33.2		$ 33.2		$ 43.3
Company contributions			$ 1.8	$ 1.9	$ 3.7	$ 3.7