Employee Pension Benefits - Schedule of Changes in Components of Accumulated Other Comprehensive Loss (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Compensation and Retirement Disclosure [Abstract]
Accumulated Other Comprehensive Income (Loss) Before Tax - Beginning Balance			$ (13,058)
Amortization of Actuarial (gains)/losses - Before Tax			1,012
Amortization of Prior service costs (credits)- Before Tax			(778)
Accumulated Other Comprehensive Income (Loss) Before Tax - Ending Balance	(12,824)		(12,824)
Income Tax Benefit (Expense) - Beginning Balance			5,128
Amortization of Actuarial (gains)/losses - Tax Effect	(182)	(259)	(393)	(531)
Amortization of Prior service costs (credits)- Tax Effect			302
Income Tax Benefit (Expense) - Ending Balance	5,037		5,037
Accumulated Other Comprehensive Income (Loss) Net of Income Tax - Beginning Balance			(7,930)
Amortization of Actuarial (gains)/losses - Net of Income Tax	286	404	619	827
Amortization of Prior service costs (credits)- Net of Income Tax	(238)	(237)	(476)	(474)
Accumulated Other Comprehensive Income (Loss) Net of Income Tax - Ending Balance	$ (7,787)		$ (7,787)