Segment Information (Summary of Segment Information) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Net interest income:
Net interest income	$ 287,496	$ 255,936	$ 828,981	$ 780,510
Net interest income, change in contribution	$ 31,560		$ 48,471
Net interest income, change in contribution (as a percent)	12.00%		6.00%
Provision for credit losses:
Provision for credit losses	$ (7,916)	25,026	$ (68,562)	213,040
Provision for credit losses, change in contribution	(32,942)		(281,602)
Non-interest income:
Non-interest income	136,474	170,593	452,353	445,828
Non-interest income, change in contribution	$ (34,119)		$ 6,525
Non-interest income, change in contribution (as a percent)	(20.00%)		1.00%
Net revenue:
Net revenue	$ 423,970	426,529	$ 1,281,334	1,226,338
Net revenue, change in contribution	$ (2,559)		$ 54,996
Net revenue, change in contribution (as a percent)	(1.00%)		4.00%
Segment profit:
Segment profit	$ 109,137	107,315	$ 367,394	191,786
Segment profit, change in contribution	$ 1,822		$ 175,608
Segment profit, change in contribution (as a percent)	2.00%		92.00%
Segment assets:
Segment assets	$ 47,832,271	43,731,718	$ 47,832,271	43,731,718	$ 45,080,768
Segment assets, change in contribution	$ 4,100,553
Segment assets, change in contribution (as a percent)	9.00%
Community banking
Segment profit:
Segment profit	$ 68,790	70,584	263,343	97,858
Segment profit, change in contribution	$ (1,794)		165,485
Segment profit, change in contribution (as a percent)	(3.00%)
Segment assets:
Segment assets	$ 38,464,169	35,729,021	38,464,169	35,729,021
Segment assets, change in contribution	$ 2,735,148
Segment assets, change in contribution (as a percent)	8.00%
Specialty finance
Segment profit:
Segment profit	$ 30,202	29,859	77,955	74,680
Segment profit, change in contribution	$ 343		$ 3,275
Segment profit, change in contribution (as a percent)	1.00%		4.00%
Segment assets:
Segment assets	$ 7,918,933	6,732,765	$ 7,918,933	6,732,765
Segment assets, change in contribution	$ 1,186,168
Segment assets, change in contribution (as a percent)	18.00%
Wealth management
Segment profit:
Segment profit	$ 10,145	6,872	26,096	19,248
Segment profit, change in contribution	$ 3,273		$ 6,848
Segment profit, change in contribution (as a percent)	48.00%		36.00%
Segment assets:
Segment assets	$ 1,449,169	1,269,932	$ 1,449,169	1,269,932
Segment assets, change in contribution	$ 179,237
Segment assets, change in contribution (as a percent)	14.00%
Operating Segments
Net interest income:
Net interest income	$ 280,649	250,151	809,124	762,169
Net interest income, change in contribution	$ 30,498		$ 46,955
Net interest income, change in contribution (as a percent)	12.00%		6.00%
Provision for credit losses:
Provision for credit losses	$ (7,916)	25,026	$ (68,562)	213,040
Provision for credit losses, change in contribution	(32,942)		(281,602)
Non-interest income:
Non-interest income	152,275	184,557	497,620	486,992
Non-interest income, change in contribution	$ (32,282)		$ 10,628
Non-interest income, change in contribution (as a percent)	(17.00%)		2.00%
Net revenue:
Net revenue	$ 432,924	434,708	$ 1,306,744	1,249,161
Net revenue, change in contribution	$ (1,784)		$ 57,583
Net revenue, change in contribution (as a percent)	0.00%		5.00%
Operating Segments | Community banking
Net interest income:
Net interest income	$ 220,007	196,803	$ 643,175	609,316
Net interest income, change in contribution	$ 23,204		$ 33,859
Net interest income, change in contribution (as a percent)	12.00%		6.00%
Provision for credit losses:
Provision for credit losses	$ (7,433)	23,342	$ (69,168)	207,168
Provision for credit losses, change in contribution	(30,775)		(276,336)
Non-interest income:
Non-interest income	94,292	136,996	331,970	347,697
Non-interest income, change in contribution	$ (42,704)		$ (15,727)
Non-interest income, change in contribution (as a percent)	(31.00%)		(5.00%)
Net revenue:
Net revenue	$ 314,299	333,799	$ 975,145	957,013
Net revenue, change in contribution	$ (19,500)		$ 18,132
Net revenue, change in contribution (as a percent)	(6.00%)		2.00%
Operating Segments | Specialty finance
Net interest income:
Net interest income	$ 52,659	46,454	$ 142,752	129,581
Net interest income, change in contribution	$ 6,205		$ 13,171
Net interest income, change in contribution (as a percent)	13.00%		10.00%
Provision for credit losses:
Provision for credit losses	$ (483)	1,684	$ 606	5,872
Provision for credit losses, change in contribution	(2,167)		$ (5,266)
Provision for credit losses, change in contribution (as a percent)			(90.00%)
Non-interest income:
Non-interest income	24,426	21,409	$ 69,999	64,548
Non-interest income, change in contribution	$ 3,017		$ 5,451
Non-interest income, change in contribution (as a percent)	14.00%		8.00%
Net revenue:
Net revenue	$ 77,085	67,863	$ 212,751	194,129
Net revenue, change in contribution	$ 9,222		$ 18,622
Net revenue, change in contribution (as a percent)	14.00%		10.00%
Operating Segments | Wealth management
Net interest income:
Net interest income	$ 7,983	6,894	$ 23,197	23,272
Net interest income, change in contribution	$ 1,089		$ (75)
Net interest income, change in contribution (as a percent)	16.00%		0.00%
Provision for credit losses:
Provision for credit losses	$ 0	0	$ 0	0
Provision for credit losses, change in contribution	$ 0		$ 0
Provision for credit losses, change in contribution (as a percent)	0.00%		0.00%
Non-interest income:
Non-interest income	$ 33,557	26,152	$ 95,651	74,747
Non-interest income, change in contribution	$ 7,405		$ 20,904
Non-interest income, change in contribution (as a percent)	28.00%		28.00%
Net revenue:
Net revenue	$ 41,540	33,046	$ 118,848	98,019
Net revenue, change in contribution	$ 8,494		$ 20,829
Net revenue, change in contribution (as a percent)	26.00%		21.00%
Intersegment Eliminations
Net interest income:
Net interest income	$ 6,847	5,785	$ 19,857	18,341
Net interest income, change in contribution	$ 1,062		$ 1,516
Net interest income, change in contribution (as a percent)	18.00%		8.00%
Provision for credit losses:
Provision for credit losses	$ 0	0	$ 0	0
Provision for credit losses, change in contribution	$ 0		$ 0
Provision for credit losses, change in contribution (as a percent)	0.00%		0.00%
Non-interest income:
Non-interest income	$ (15,801)	(13,964)	$ (45,267)	(41,164)
Non-interest income, change in contribution	$ (1,837)		$ (4,103)
Non-interest income, change in contribution (as a percent)	13.00%		10.00%
Net revenue:
Net revenue	$ (8,954)	$ (8,179)	$ (25,410)	$ (22,823)
Net revenue, change in contribution	$ (775)		$ (2,587)
Net revenue, change in contribution (as a percent)	9.00%		11.00%