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, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Total	$ 20,336	$ 21,425	$ 22,858
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	243	833
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	18,334	18,623
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	1,759	1,969
Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	243	833
Cash [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	243	833
Pooled Pension Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	11,760	12,397
Pooled Pension Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	11,760	12,397
Pooled Fixed Pension Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	6,015	5,740
Pooled Fixed Pension Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	6,015	5,740
Real Estate Pooled Pension Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	559	486
Real Estate Pooled Pension Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	559	486
Insurance Contracts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	1,759	1,969
Insurance Contracts [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	$ 1,759	$ 1,969