Stockholders' Equity and EPS - Reconciliation of Basic EPS to Diluted EPS (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017		Mar. 31, 2016
Numerator:
Net income available to common stockholders	$ 101,483	[1]	$ 79,174
Denominator:
Weighted average common shares outstanding-basic (in shares)	52,344		51,646
Denominator for diluted calculation (in shares)	53,179		52,085
Earnings per common share:
Basic (dollars per share)	$ 1.94	[1]	$ 1.53
Diluted (dollars per share)	$ 1.91	[1]	$ 1.52
Stock options and ESPP
Denominator:
Weighted average effect of dilutive securities (in shares)	440		264
Restricted stock units
Denominator:
Weighted average effect of dilutive securities (in shares)	395		175

[1] Included in income tax expense, net income available to common shareholders, earnings per common share-basic and earnings for common share-diluted, for the three months ended March 31, 2017, are tax benefits recognized associated with the adoption of Accounting Standards Update ("ASU") 2016-09, Improvements to Employee Share-Based Payment Accounting in the first quarter of 2017. This guidance was adopted on a prospective basis with no change to prior period amounts.