Calculation of 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
Earnings Per Share [Abstract]
Net income	$ 75,140	$ 63,089	$ 136,691	$ 118,952
Income allocated to participating securities-basic		1		4
Net income available to common stockholders-basic	75,140	63,088	136,691	118,948
Basic weighted average shares	134,699	136,385	135,014	136,845
Basic net income per share	$ 0.56	$ 0.46	$ 1.01	$ 0.87
Net income	75,140	63,089	136,691	118,952
Income allocated to participating securities-diluted		1		4
Net income available to common stockholders-diluted	$ 75,140	$ 63,088	$ 136,691	$ 118,948
Basic weighted average shares	134,699	136,385	135,014	136,845
Dilutive effect of potential common shares	1,009	1,274	918	1,179
Diluted weighted average shares	135,708	137,659	135,932	138,024
Diluted net income per share	$ 0.55	$ 0.46	$ 1.01	$ 0.86