Pension and Other Postretirement Benefits - Contributions for Pension and Other Postretirement Benefits (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
U.K. Defined Benefit Pension Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Contributions	$ 427	$ 466
Other Postretirement Benefit Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Contributions	164	137
U.K. Defined Contribution Pension Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Contributions	$ 96	$ 92