Other Postretirement Benefit Plans - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2013 Age
Compensation And Retirement Disclosure [Abstract]
Minimum year of service to qualify for postretirement medical benefits	20 years
Minimum age to qualify for postretirement medical benefits	60
Condition to qualify for postretirement medical benefits	Employees who had worked 20 years and attained a minimum age of 60 by September 1, 2000