Weighted-Average Shares Outstanding for Computation of Basic and Diluted Income Per Common Share (Detail)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010		Dec. 31, 2009
Earnings Per Share Disclosure [Line Items]
Basic method	193,409,621	191,830,357	[1]	190,767,077	[1]
Dilutive stock options	1,102,781	1,327,457		1,701,373
Diluted method	194,512,402	193,157,814	[1]	192,468,450	[1]

[1] Reclassified to conform to current presentation.