Reconciliation of income tax computed at US Federal tax rates (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Statutory Income Tax	35.00%	35.00%	35.00%
Prior Year Taxes	(0.90%)	(11.00%)	0.40%
Foreign Items	(2.00%)	(0.30%)	(1.30%)
Tax Credits	(2.70%)	(5.90%)	(0.60%)
Other Items, Net	(1.00%)	(3.10%)	(0.10%)
Effective Tax	28.40%	14.70%	33.40%