Benefit Obligations - Amounts Recognized in Consolidated Balance Sheets for Plans (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Non-current liabilities	$ (559,252)	$ (597,183)
Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Non-current assets	1,863	2,201
Current liabilities	(873)	(856)
Non-current liabilities	(559,252)	(597,183)
Net (liability)/asset	(558,262)	(595,838)
Post-retirement Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Non-current assets	14,328	9,034
Current liabilities
Non-current liabilities
Net (liability)/asset	$ 14,328	$ 9,034