Calculation of Basic and Diluted Net Income per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
BASIC EPS:
Net income	$ 54,283	$ 40,768	$ 89,105	$ 96,998
Adjust for income attributed to holders of non-vested restricted stock	(559)	(392)	(910)	(882)
Income attributed to common stockholders	53,724	40,376	88,195	96,116
Weighted average number of common shares outstanding, excluding non-vested shares of restricted stock	143,622	145,465	143,259	145,148
Basic net income per common share	$ 0.37	$ 0.28	$ 0.62	$ 0.66
DILUTED EPS:
Income attributed to common stockholders	$ 53,724	$ 40,376	$ 88,195	$ 96,116
Weighted average number of common shares outstanding, excluding non-vested shares of restricted stock	143,622	145,465	143,259	145,148
Add dilutive effect of potential common shares	2,407	909	2,327	1,144
Weighted average number of diluted common shares outstanding	146,029	146,374	145,586	146,292
Diluted net income per common share	$ 0.37	$ 0.28	$ 0.61	$ 0.66
Potentially dilutive securities excluded as anti-dilutive	432	4,015	432	4,065