Unaudited Quarterly Financial Data Supplemental Consolidated Financial Information (Detail) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 279,232	$ 264,791	$ 253,926	$ 248,816	$ 243,725	$ 229,326	$ 213,841	$ 205,024	$ 1,046,765		$ 891,916		$ 729,621
Interest expense	(10,163)	(10,131)	(10,155)	(9,891)	(8,988)	(8,761)	(8,876)	(8,696)	(40,340)		(35,321)		(32,277)
Net interest income	269,069	254,660	243,771	238,925	234,737	220,565	204,965	196,328	1,006,425		856,595		697,344
Provision for loan losses	31,261	33,403	26,513	6,452	40,435	16,610	1,947	494	97,629		59,486		63,693
Noninterest income	114,506	108,477	126,287	123,524	167,637	80,167	14,210	310,225	472,794		572,239		673,206
Noninterest expense	(208,608)	(184,755)	(194,112)	(190,541)	(186,067)	(179,761)	(170,944)	(170,408)	(778,016)	[1]	(707,180)	[1]	(615,244)	[1]
Income before income tax expense	143,706	144,979	149,433	165,456	175,872	104,361	46,284	335,651
Income tax expense	(53,697)	(57,017)	(54,974)	(63,066)	(46,077)	(40,207)	(35,928)	(61,296)	(228,754)	[1]	(183,508)	[1]	(146,830)	[1]
Net income before noncontrolling interests	90,009	87,962	94,459	102,390	129,795	64,154	10,356	274,355	374,820	[1],[2],[3],[4]	478,660	[1],[3],[4],[5],[6]	544,783	[1],[3],[4],[5],[6]
Net income attributable to noncontrolling interests	(2,497)	(6,229)	(8,316)	(13,874)	(71,805)	(177)	40,597	(183,405)	(30,916)	[2],[3]	(214,790)	[3]	(330,266)	[3]
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	[1]	$ 214,517	[1]
Earnings per common share—basic, in dollars per share	$ 1.70	$ 1.59	$ 1.68	$ 1.74	$ 1.14	$ 1.26	$ 1.06	$ 1.98	$ 6.70	[1]	$ 5.39	[1]	$ 4.73	[1]
Earnings per common share—diluted, in dollars per share	$ 1.68	$ 1.57	$ 1.66	$ 1.71	$ 1.13	$ 1.24	$ 1.04	$ 1.95	$ 6.62	[1]	$ 5.31	[1]	$ 4.67	[1]

[1] 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.

[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.

[3] 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.

[4] 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.

[5] Cash flows for the years ended December 31, 2014 and 2013 were revised to reflect the retrospective application of our adoption of ASU 2014-01.

[6] See Note 2— "Summary of Significant Accounting Policies-Adoptions of New Accounting Standards” of the “Notes to the Consolidated Financial Statements” under Part II, Item 8 of this report for additional details.