Postretirement Benefit Plans - Defined Benefit Pension Plans - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2020 USD ($)
Defined Contribution Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Balance of trust assets	$ 1,740,000
United States [Member] | Unfunded Plan [Member] | Non-qualified Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected contributions or payments to defined benefit plans	299,000
Employer contributions or payments	195,000
U.K Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected contributions or payments to defined benefit plans	495,000
Employer contributions or payments	$ 284,000