Per Share Information - Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
AMOUNTS ATTRIBUTABLE TO COMMON STOCK:
Net income from continuing operations	$ 72,081	$ 45,798
Net loss from discontinued operations		(91)
Net income attributable to common stock	$ 72,081	$ 45,707
WEIGHTED AVERAGE SHARES:
Weighted average shares outstanding for basic earnings per share	213,453	211,481
Effect of dilutive stock options	59	111
Weighted average shares outstanding for diluted earnings per share	213,512	211,592