Calculation of Basic and Diluted Net Income Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
BASIC EPS:
Net income	$ 56,230	$ 97,274
Adjust for income attributed to holders of non-vested restricted stock	(482)	(742)
Income attributed to common stockholders	55,748	96,532
Weighted average number of common shares outstanding, excluding non-vested shares of restricted stock	144,827	154,625
Basic net income per common share	$ 0.38	$ 0.62
DILUTED EPS:
Income attributed to common stockholders	55,748	96,532
Add incremental earnings related to potential common shares	6
Adjusted income attributed to common stockholders	$ 55,754	$ 96,532
Weighted average number of common shares outstanding, excluding non-vested shares of restricted stock	144,827	154,625
Add dilutive effect of potential common shares	1,956	776
Weighted average number of diluted common shares outstanding	146,783	155,401
Diluted net income per common share	$ 0.38	$ 0.62
Potentially dilutive securities excluded as anti-dilutive	1,874	3,229