Stockholders' Equity and EPS Reconciliation of Basic EPS to Diluted EPS (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Numerator:
Net income available to common stockholders	$ 87,512	$ 81,733	$ 86,143	$ 88,516	$ 57,990	$ 63,977	$ 50,953	$ 90,950	$ 343,904	[1],[2]	$ 263,870	[2]	$ 214,517	[2]
Denominator:
Weighted average common shares outstanding-basic (in shares)									51,318		48,931		45,309
Denominator for diluted calculation (in shares)									51,916		49,662		45,944
Earnings per common share:
Basic (usd per share)	$ 1.70	$ 1.59	$ 1.68	$ 1.74	$ 1.14	$ 1.26	$ 1.06	$ 1.98	$ 6.70	[2]	$ 5.39	[2]	$ 4.73	[2]
Diluted (usd per share)	$ 1.68	$ 1.57	$ 1.66	$ 1.71	$ 1.13	$ 1.24	$ 1.04	$ 1.95	$ 6.62	[2]	$ 5.31	[2]	$ 4.67	[2]
Stock options and ESPP
Denominator:
Weighted average effect of dilutive securities (in shares)									387		485		431
Restricted stock units
Denominator:
Weighted average effect of dilutive securities (in shares)									211		246		204

[1] During the second quarter of 2015 we adopted new accounting guidance related to our consolidated variable interest entities (ASU 2015-02). Amounts prior to January 1, 2015 have not been revised for the adoption of this guidance. See Note 2— "Summary of Significant Accounting Policies” of the “Notes to the Consolidated Financial Statements” under Part II, Item 8 of this report for additional details.

[2] Prior period amounts have been revised to reflect the retrospective application of new accounting guidance adopted in the first quarter of 2015 related to our investments in qualified affordable housing projects (ASU 2014-01). See Note 2— "Summary of Significant Accounting Policies” of the “Notes to the Consolidated Financial Statements” under Part II, Item 8 of this report for additional details.