Weighted-Average Shares Outstanding for Computation of Basic and Diluted Income Per Common Share (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011		Dec. 31, 2010
Earnings Per Share Disclosure [Line Items]
Basic method	193,902,335	193,409,621	[1]	191,830,357	[1]
Dilutive stock options	766,402	1,102,781		1,327,457
Diluted method	194,668,737	194,512,402	[1]	193,157,814	[1]

[1] Reclassified to conform to current presentation.