Parent Company Only Condensed Financial Information Condensed Statement of Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014
Schedule of Condensed Consolidating Statement of Operations [Line Items]
Interest income	$ 307,333	$ 300,413	$ 293,992	$ 291,658	$ 279,232	$ 264,791	$ 253,926	$ 248,816	$ 1,193,396	$ 1,046,765		$ 891,916
Interest expense	(10,728)	(11,252)	(10,656)	(10,237)	(10,163)	(10,131)	(10,155)	(9,891)	(42,873)	(40,340)		(35,321)
Gains on derivative instruments, net									48,581	83,805		96,845
Gains on investment securities, net									51,740	89,445	[1],[2]	267,023
Fund management fees									19,195	15,941		13,498
Impairment loss on SVBIF Sale Transaction									0	0		(13,934)
Income tax expense	(54,825)	(76,877)	(65,047)	(53,584)	(53,697)	(57,017)	(54,974)	(63,066)	(250,333)	(228,754)		(183,508)
Net income available to common stockholders	$ 99,466	$ 111,081	$ 92,964	$ 79,174	$ 87,512	$ 81,733	$ 86,143	$ 88,516	382,685	343,904		263,870
Parent Company
Schedule of Condensed Consolidating Statement of Operations [Line Items]
Interest income									690	964		2,534
Interest expense									(35,316)	(34,169)		(21,863)
Dividend income from subsidiary									40,000	0		0
Gains on derivative instruments, net									35,608	55,477		66,604
Gains on investment securities, net									20,644	39,447		8,750
Fund management fees									24,197	17,772		13,960
Impairment loss on SVBIF Sale Transaction									0	0		(9,564)
General and administrative expenses									(55,139)	(54,822)		(53,912)
Income tax expense									423	(14,448)		(15,038)
Loss before net income of subsidiaries									31,107	10,221		(8,529)
Net income available to common stockholders									382,685	343,904		263,870
Parent Company | Nonbank Subsidiaries
Schedule of Condensed Consolidating Statement of Operations [Line Items]
Loss before net income of subsidiaries									11,949	26,819		23,049
Equity in undistributed net income of subsidiary									11,949	26,819		23,049
Parent Company | Bank Subsidiaries
Schedule of Condensed Consolidating Statement of Operations [Line Items]
Loss before net income of subsidiaries									379,629	306,864		249,350
Equity in undistributed net income of subsidiary									$ 339,629	$ 306,864		$ 249,350

[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] 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.