Postretirement Benefit Plans - Schedule of Amounts Recognized in Balance Sheets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
United States [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Non-current asset		$ 818
Current liability	(185)	(185)
Non-current liability	(42,853)	(11,877)
Net amount recognized	(43,038)	(11,244)
United Kingdom [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Non-current asset		1,109
Non-current liability	(125)
Net amount recognized	$ (125)	$ 1,109