Postretirement Benefit Plans - Company's Asset Allocations for its U.K. Pension Plans by Asset Category (Detail) (United Kingdom [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Total	$ 22,858	$ 22,204	$ 18,390
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	1,176	412
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	19,441	19,366
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	2,241	2,426
Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	1,176	412
Cash [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	1,176	412
Pooled Pension Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	15,322	15,397
Pooled Pension Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	15,322	15,397
Pooled Fixed Pension Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	3,642	3,550
Pooled Fixed Pension Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	3,642	3,550
Real Estate Pooled Pension Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	477	419
Real Estate Pooled Pension Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	477	419
Insurance Contracts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	2,241	2,426
Insurance Contracts [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	$ 2,241	$ 2,426