Stockholders' Equity and EPS - Reconciliation of Basic EPS to Diluted EPS (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Numerator:
Net income available to common stockholders	$ 91,301	$ 40,891
Denominator:
Weighted average common shares outstanding-basic (in shares)	45,866	44,802
Denominator for diluted calculation (in shares)	46,725	45,393
Earnings per common share:
Basic (dollars per share)	$ 1.99	$ 0.91
Diluted (dollars per share)	$ 1.95	$ 0.90
Stock options and ESPP
Denominator:
Weighted average effect of dilutive securities (in shares)	566	402
Restricted stock units
Denominator:
Weighted average effect of dilutive securities (in shares)	293	189