Reconciliation of Basic EPS to Diluted EPS (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011		Jun. 30, 2012	Jun. 30, 2011
Numerator:
Net income available to common stockholders	$ 47,603	$ 65,750		$ 82,393	$ 98,757
Denominator:
Weighted average common shares outstanding-basic	44,207	42,924		43,994	42,704
3.875% Convertible Notes		61	[1]		77	[1]
Denominator for diluted calculation	44,712	43,740		44,573	43,559
Earnings per common share:
Basic	$ 1.08	$ 1.53		$ 1.87	$ 2.31
Diluted	$ 1.06	$ 1.50		$ 1.85	$ 2.27
Stock options and ESPP
Denominator:
Weighted average effect of dilutive securities	385	654		426	678
Restricted stock units
Denominator:
Weighted average effect of dilutive securities	120	101		153	100

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