Employee Pension Benefits - Schedule of Changes in Components of Accumulated Other Comprehensive Loss (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Compensation and Retirement Disclosure [Abstract]
Accumulated Other Comprehensive Income (Loss) Before Tax - Beginning Balance	$ (13,058)
Amortization of Actuarial (gains)/losses - Before Tax	544
Amortization of Prior service costs (credits)- Before Tax	(389)
Accumulated Other Comprehensive Income (Loss) Before Tax - Ending Balance	(12,903)
Income Tax Benefit (Expense) - Beginning Balance	5,128
Amortization of Actuarial (gains)/losses - Tax Effect	(211)	(272)
Amortization of Prior service costs (credits)- Tax Effect	151
Income Tax Benefit (Expense) - Ending Balance	5,068
Accumulated Other Comprehensive Income (Loss) Net of Income Tax - Beginning Balance	(7,930)
Amortization of Actuarial (gains)/losses - Net of Income Tax	333	423
Amortization of Prior service costs (credits)- Net of Income Tax	(238)	(237)
Accumulated Other Comprehensive Income (Loss) Net of Income Tax - Ending Balance	$ (7,835)