Pension and Other Postretirement Benefits - Contributions for Pension and Other Postretirement Benefits (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
U.S. Pension Benefits Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Contributions	$ 0	$ 0
U.K. Pension Benefits Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Contributions	870	888
Other Postretirement Benefits (e.g. Net Payments) [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Contributions	281	289
U.K. Defined Contribution Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Contributions	$ 146	$ 152