Stockholders' Equity - Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Earnings Per Share [Abstract]
Net income	$ 80,511	$ 74,601	$ 329,142
Denominator:
Weighted average number of common shares used in basic EPS	168,078,589	164,836,992
Effect of dilutive shares:
Potential common shares issuable from stock options and stock awards	4,682,052	6,513,828
Weighted average number of common shares and dilutive potential common shares used in diluted EPS	172,760,641	171,350,820
Basic net income per share	$ 0.48	$ 0.45
Diluted net income per share	$ 0.47	$ 0.44