Postretirement Benefit Plans - Company's Asset Allocations for its U.K. Pension Plans by Asset Category (Detail) - United Kingdom [Member] - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Total	$ 20,576	$ 24,168	$ 20,336
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	205	745
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	19,128	21,725
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	1,243	1,698
Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	205	745
Cash [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	205	745
Pooled Pension Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	12,750	14,127
Pooled Pension Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	12,750	14,127
Pooled Fixed Pension Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	6,378	6,952
Pooled Fixed Pension Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	6,378	6,952
Real Estate Pooled Pension Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total		646
Real Estate Pooled Pension Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total		646
Insurance Contracts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	1,243	1,698
Insurance Contracts [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	$ 1,243	$ 1,698