Postretirement Benefit Plans - Defined Benefit Pension Plans - Additional Information (Detail)	3 Months Ended	9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)
U.S Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 2,100,000	$ 2,100,000
Expected payment related to qualified plan	0	0
Expected payment related to non-qualified plan	312,000	312,000
Payments related to non-qualified plans	256,000	256,000
U.K Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions		281,000
Expected payment related to qualified plan	$ 360,000	$ 360,000