Weighted-Average Assumptions Used in Measurement of Company's Benefit Obligation (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	6.20%
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefit Obligation, Discount rate	4.24%	5.00%
Expected return on plan assets	6.20%	6.48%
Benefit Obligation, Rate of compensation increase	4.13%	4.22%
Net periodic benefit expense, Discount rate	4.80%	5.50%
Net periodic benefit expense, Rate of compensation increase	4.10%	4.22%
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefit Obligation, Discount rate	4.18%	4.87%
Expected return on plan assets	0.00%	0.00%
Benefit Obligation, Rate of compensation increase	0.00%	0.00%
Net periodic benefit expense, Discount rate	4.87%	5.50%
Net periodic benefit expense, Rate of compensation increase	0.00%	0.00%