Pension and Other Post-Retirement Benefits - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($)
Funded Pension Plans [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit payment amount	$ 10.4
Unfunded Pension Plans [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit payment amount	3.5
Anticipated future payments	2.3
Other Postretirement Benefit Plans Defined Benefit [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit payment amount	0.7
Anticipated future payments	$ 0.3