Stockholders' Equity and EPS - Reconciliation of Basic EPS to Diluted EPS (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2017		Jun. 30, 2016	Jun. 30, 2017		Jun. 30, 2016
Numerator:
Net income available to common stockholders	$ 123,193	[1]	$ 92,964	$ 224,676	[1]	$ 172,138
Denominator:
Weighted average common shares outstanding-basic (in shares)	52,537		51,831	52,441		51,739
Denominator for diluted calculation (in shares)	53,194		52,187	53,180		52,130
Earnings per common share:
Basic (dollars per share)	$ 2.34	[1]	$ 1.79	$ 4.28	[1]	$ 3.33
Diluted (dollars per share)	$ 2.32	[1]	$ 1.78	$ 4.22	[1]	$ 3.30
Stock options and ESPP
Denominator:
Weighted average effect of dilutive securities (in shares)	368		238	397		246
Restricted stock units
Denominator:
Weighted average effect of dilutive securities (in shares)	289		118	342		145

[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 and six months ended June 30, 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.