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		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Numerator:
Net income available to common stockholders	$ 50,797	$ 48,584	$ 142,098	$ 89,475
Denominator:
Weighted average common shares outstanding-basic (in shares)	48,168	45,164	47,025	44,985
Denominator for diluted calculation (in shares)	49,045	45,684	47,987	45,537
Earnings per common share:
Basic (dollars per share)	$ 1.05	$ 1.08	$ 3.02	$ 1.99
Diluted (dollars per share)	$ 1.04	$ 1.06	$ 2.96	$ 1.96
Stock options and ESPP
Denominator:
Weighted average effect of dilutive securities (in shares)	569	380	601	384
Restricted stock units
Denominator:
Weighted average effect of dilutive securities (in shares)	308	140	361	168