Segment Information (Summary of Segment Information) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Net interest income:
Net interest income	$ 261,895	$ 261,443
Net interest income, Change in Contribution	$ 452
Net interest income, Change in Contribution (as a percent)	0.00%
Provision for credit losses:
Provision for credit losses	$ (45,347)	52,961
Provision for credit losses, Change in Contribution	$ (98,308)
Provision for credit losses, Change in Contribution (as a percent)	(186.00%)
Non-interest income:
Non-interest income	$ 186,506	113,242
Non-interest income, Change in Contribution	$ 73,264
Non-interest income, Change in Contribution (as a percent)	65.00%
Net revenue:
Net revenue	$ 448,401	374,685
Net revenue, Change in Contribution	$ 73,716
Net revenue, Change in Contribution (as a percent)	20.00%
Segment profit:
Segment profit	$ 153,148	62,812
Segment profit, Change in Contribution	$ 90,336
Segment profit, Change in Contribution (as a percent)	144.00%
Segment assets:
Segment assets	$ 45,682,202	38,799,847	$ 45,080,768
Segment assets, Change in Contribution	$ 6,882,355
Segment assets, Change in Contribution (as a percent)	18.00%
Community banking
Segment profit:
Segment profit	$ 121,801	34,589
Segment profit, Change in Contribution	$ 87,212
Segment profit, Change in Contribution (as a percent)	252.00%
Segment assets:
Segment assets	$ 37,102,603	31,499,899
Segment assets, Change in Contribution	$ 5,602,704
Segment assets, Change in Contribution (as a percent)	18.00%
Specialty finance
Segment profit:
Segment profit	$ 23,903	22,133
Segment profit, Change in Contribution	$ 1,770
Segment profit, Change in Contribution (as a percent)	8.00%
Segment assets:
Segment assets	$ 7,174,269	6,133,548
Segment assets, Change in Contribution	$ 1,040,721
Segment assets, Change in Contribution (as a percent)	17.00%
Wealth management
Segment profit:
Segment profit	$ 7,444	6,090
Segment profit, Change in Contribution	$ 1,354
Segment profit, Change in Contribution (as a percent)	22.00%
Segment assets:
Segment assets	$ 1,405,330	1,166,400
Segment assets, Change in Contribution	$ 238,930
Segment assets, Change in Contribution (as a percent)	20.00%
Operating Segments
Net interest income:
Net interest income	$ 255,837	255,339
Net interest income, Change in Contribution	$ 498
Net interest income, Change in Contribution (as a percent)	0.00%
Provision for credit losses:
Provision for credit losses	$ (45,347)	52,961
Provision for credit losses, Change in Contribution	$ (98,308)
Provision for credit losses, Change in Contribution (as a percent)	(186.00%)
Non-interest income:
Non-interest income	$ 200,628	126,441
Non-interest income, Change in Contribution	$ 74,187
Non-interest income, Change in Contribution (as a percent)	59.00%
Net revenue:
Net revenue	$ 456,465	381,780
Net revenue, Change in Contribution	$ 74,685
Net revenue, Change in Contribution (as a percent)	20.00%
Operating Segments | Community banking
Net interest income:
Net interest income	$ 203,489	206,835
Net interest income, Change in Contribution	$ (3,346)
Net interest income, Change in Contribution (as a percent)	(2.00%)
Provision for credit losses:
Provision for credit losses	$ (46,572)	51,677
Provision for credit losses, Change in Contribution	$ (98,249)
Provision for credit losses, Change in Contribution (as a percent)	(190.00%)
Non-interest income:
Non-interest income	$ 147,268	81,003
Non-interest income, Change in Contribution	$ 66,265
Non-interest income, Change in Contribution (as a percent)	82.00%
Net revenue:
Net revenue	$ 350,757	287,838
Net revenue, Change in Contribution	$ 62,919
Net revenue, Change in Contribution (as a percent)	22.00%
Operating Segments | Specialty finance
Net interest income:
Net interest income	$ 44,899	40,712
Net interest income, Change in Contribution	$ 4,187
Net interest income, Change in Contribution (as a percent)	10.00%
Provision for credit losses:
Provision for credit losses	$ 1,225	1,284
Provision for credit losses, Change in Contribution	$ (59)
Provision for credit losses, Change in Contribution (as a percent)	(5.00%)
Non-interest income:
Non-interest income	$ 23,109	21,308
Non-interest income, Change in Contribution	$ 1,801
Non-interest income, Change in Contribution (as a percent)	8.00%
Net revenue:
Net revenue	$ 68,008	62,020
Net revenue, Change in Contribution	$ 5,988
Net revenue, Change in Contribution (as a percent)	10.00%
Operating Segments | Wealth management
Net interest income:
Net interest income	$ 7,449	7,792
Net interest income, Change in Contribution	$ (343)
Net interest income, Change in Contribution (as a percent)	(4.00%)
Provision for credit losses:
Provision for credit losses	$ 0	0
Provision for credit losses, Change in Contribution	$ 0
Provision for credit losses, Change in Contribution (as a percent)	0.00%
Non-interest income:
Non-interest income	$ 30,251	24,130
Non-interest income, Change in Contribution	$ 6,121
Non-interest income, Change in Contribution (as a percent)	25.00%
Net revenue:
Net revenue	$ 37,700	31,922
Net revenue, Change in Contribution	$ 5,778
Net revenue, Change in Contribution (as a percent)	18.00%
Intersegment Eliminations
Net interest income:
Net interest income	$ 6,058	6,104
Net interest income, Change in Contribution	$ (46)
Net interest income, Change in Contribution (as a percent)	(1.00%)
Provision for credit losses:
Provision for credit losses	$ 0	0
Provision for credit losses, Change in Contribution	$ 0
Provision for credit losses, Change in Contribution (as a percent)	0.00%
Non-interest income:
Non-interest income	$ (14,122)	(13,199)
Non-interest income, Change in Contribution	$ (923)
Non-interest income, Change in Contribution (as a percent)	7.00%
Net revenue:
Net revenue	$ (8,064)	$ (7,095)
Net revenue, Change in Contribution	$ (969)
Net revenue, Change in Contribution (as a percent)	14.00%