Calculation of Income (Loss) Per Share From Continuing and Discontinued Operations (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
BASIC EPS:
Income from continuing operations	$ 50,806	$ 81,928	$ 240,618	$ 235,185
Adjust for income attributed to holders of non-vested restricted stock	(462)	(705)	(2,040)	(1,841)
Income from continuing operations attributed to common stockholders	50,344	81,223	238,578	233,344
Loss from discontinued operations, net				(367)
Adjust for loss attributed to holders of non-vested restricted stock				3
Loss from discontinued operations attributed to common stockholders				(364)
Weighted average number of common shares outstanding, excluding non-vested shares of restricted stock	149,846	152,617	152,570	153,661
Basic income from continuing operations per common share	$ 0.34	$ 0.53	$ 1.56	$ 1.52
Basic loss from discontinued operations per common share	$ 0.00	$ 0.00	$ 0.00	$ 0.00
Basic net income per common share	$ 0.34	$ 0.53	$ 1.56	$ 1.52
DILUTED EPS:
Income from continuing operations attributed to common stockholders	50,344	81,223	238,578	233,344
Add incremental earnings related to potential common shares		6
Adjusted income from continuing operations attributed to common stockholders	$ 50,344	$ 81,229	$ 238,578	$ 233,344
Weighted average number of common shares outstanding, excluding non-vested shares of restricted stock	149,846	152,617	152,570	153,661
Add dilutive effect of potential common shares	676	1,503	496	1,708
Weighted average number of diluted common shares outstanding	150,522	154,120	153,066	155,369
Diluted income from continuing operations per common share	$ 0.33	$ 0.53	$ 1.56	$ 1.50
Diluted loss from discontinued operations per common share	$ 0.00	$ 0.00	$ 0.00	$ 0.00
Diluted net income per common share	$ 0.33	$ 0.53	$ 1.56	$ 1.50
Potentially dilutive securities excluded as anti-dilutive	5,538	410	5,498	1,707