Stockholders' Equity - Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Numerator used in basic and diluted EPS:
Net income	$ 96,441	$ 82,911	$ 261,157	$ 230,843	$ 329,142
Denominator:
Weighted average number of common shares used in basic EPS	168,044,100	165,978,080	168,089,919	165,587,027
Effect of dilutive shares:
Potential common shares issuable from stock options and stock awards	4,110,453	5,682,463	4,371,041	6,050,544
Weighted average number of common shares and dilutive potential common shares used in diluted EPS	172,154,553	171,660,543	172,460,960	171,637,571
Basic net income per share (in dollars per share)	$ 0.57	$ 0.50	$ 1.55	$ 1.39
Diluted net income per share (in dollars per share)	$ 0.56	$ 0.48	$ 1.51	$ 1.34