Reconciliation of Basic EPS to Diluted EPS (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Numerator:
Net income available to common stockholders	$ 42,289		$ 37,571		$ 124,682		$ 136,328
Denominator:
Weighted average common shares outstanding-basic	44,449		43,233		44,147		42,882
3.875% Convertible Notes	0	[1]	0	[1]	0	[1]	27	[1]
Denominator for diluted calculation	44,915		43,791		44,692		43,641
Earnings per common share:
Basic	$ 0.95		$ 0.87		$ 2.82		$ 3.18
Diluted	$ 0.94		$ 0.86		$ 2.79		$ 3.12
Stock options and ESPP
Denominator:
Weighted average effect of dilutive securities	346		452		402		610
Restricted stock units
Denominator:
Weighted average effect of dilutive securities	120		106		143		122

[1] Our $250 million 3.875% Convertible Notes matured on April 15, 2011.