Reconciliation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Numerator:
Net income used for calculating basic and diluted earnings per share	$ 30,464		$ 20,075		$ 91,878		$ 59,591
Denominator:
Weighted average number of common shares used in the calculation of basic earnings per share	96,057		95,473		96,462		95,698
Common stock equivalents associated with stock-based compensation plans	2,202	[1],[2]	3,324	[1],[2]	3,005	[1],[2]	3,886	[1],[2]
Shares used in the calculation of diluted earnings per share	98,259		98,797		99,467		99,584
Basic earnings per share	$ 0.32		$ 0.21		$ 0.95		$ 0.62
Diluted earnings per share	$ 0.31		$ 0.20		$ 0.92		$ 0.60

[1] For the nine months ended September 30, 2011 and 2010, 0.3 million and 0.5 million of common stock equivalents, respectively, were not included in the computation of diluted earnings per share because the effect would have been anti-dilutive.

[2] For the three months ended September 30, 2011 and 2010, 1.6 million and 1.0 million of common stock equivalents, respectively, were not included in the computation of diluted earnings per share because the effect would have been anti-dilutive.