Employee Benefit Plans - Assumptions Used in Measuring Net Periodic Benefit Costs (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Weighted average discount rate	5.17%	5.74%	6.54%
Rate of increase in future compensation levels	3.30%	3.39%	3.75%
Expected long-term rate of return on plan assets	7.84%	7.87%	8.00%
Other Postretirement Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Weighted average discount rate	4.00%	4.25%	5.20%
Rate of increase in future compensation levels
Expected long-term rate of return on plan assets