Reconciliation of Basic EPS to Diluted EPS (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 available to common stockholders	$ 37,571	$ 37,787	$ 136,328	$ 77,464
Denominator:
Weighted average common shares outstanding-basic	43,233	41,930	42,882	41,679
3.875% Convertible Notes			27
Denominator for diluted calculation	43,791	42,513	43,641	42,401
Earnings per common share:
Basic	$ 0.87	$ 0.90	$ 3.18	$ 1.86
Diluted	$ 0.86	$ 0.89	$ 3.12	$ 1.83
Stock options and ESPP
Denominator:
Weighted average effect of dilutive securities	452	511	610	652
Restricted stock units
Denominator:
Weighted average effect of dilutive securities	106	72	122	70