Segment Information (Summary of Segment Information) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Net interest income:
Net interest income	$ 255,936	$ 264,852	$ 780,510	$ 793,040
Net interest income, Change in Contribution	$ (8,916)		$ (12,530)
Net interest income, Change in Contribution (as a percent)	(3.00%)		(2.00%)
Non-interest income:
Non-interest income	$ 170,593	115,137	$ 445,828	294,952
Non-interest income, Change in Contribution	$ 55,456		$ 150,876
Non-interest income, Change in Contribution (as a percent)	48.00%		51.00%
Net revenue:
Net revenue	$ 426,529	379,989	$ 1,226,338	1,087,992
Net revenue, Change in Contribution	$ 46,540		$ 138,346
Net revenue, Change in Contribution (as a percent)	12.00%		13.00%
Segment profit:
Segment profit	$ 107,315	99,121	$ 191,786	269,733
Segment profit, Change in Contribution	$ 8,194		$ (77,947)
Segment profit, Change in Contribution (as a percent)	8.00%		(29.00%)
Segment assets:
Segment assets	$ 43,731,718	34,911,902	$ 43,731,718	34,911,902	$ 36,620,583
Segment assets, Change in Contribution	$ 8,819,816
Segment assets, Change in Contribution (as a percent)	25.00%
Community banking
Segment profit:
Segment profit	$ 70,584	68,792	97,858	182,553
Segment profit, Change in Contribution	$ 1,792		$ (84,695)
Segment profit, Change in Contribution (as a percent)	3.00%		(46.00%)
Segment assets:
Segment assets	$ 35,729,021	28,092,785	$ 35,729,021	28,092,785
Segment assets, Change in Contribution	$ 7,636,236
Segment assets, Change in Contribution (as a percent)	27.00%
Specialty finance
Segment profit:
Segment profit	$ 29,859	24,241	74,680	67,218
Segment profit, Change in Contribution	$ 5,618		$ 7,462
Segment profit, Change in Contribution (as a percent)	23.00%		11.00%
Segment assets:
Segment assets	$ 6,732,765	5,739,798	$ 6,732,765	5,739,798
Segment assets, Change in Contribution	$ 992,967
Segment assets, Change in Contribution (as a percent)	17.00%
Wealth management
Segment profit:
Segment profit	$ 6,872	6,088	19,248	19,962
Segment profit, Change in Contribution	$ 784		$ (714)
Segment profit, Change in Contribution (as a percent)	13.00%		(4.00%)
Segment assets:
Segment assets	$ 1,269,932	1,079,319	$ 1,269,932	1,079,319
Segment assets, Change in Contribution	$ 190,613
Segment assets, Change in Contribution (as a percent)	18.00%
Operating Segments
Net interest income:
Net interest income	$ 250,151	259,340	762,169	776,614
Net interest income, Change in Contribution	$ (9,189)		$ (14,445)
Net interest income, Change in Contribution (as a percent)	(4.00%)		(2.00%)
Non-interest income:
Non-interest income	$ 184,557	127,295	$ 486,992	330,102
Non-interest income, Change in Contribution	$ 57,262		$ 156,890
Non-interest income, Change in Contribution (as a percent)	45.00%		48.00%
Net revenue:
Net revenue	$ 434,708	386,635	$ 1,249,161	1,106,716
Net revenue, Change in Contribution	$ 48,073		$ 142,445
Net revenue, Change in Contribution (as a percent)	12.00%		13.00%
Operating Segments | Community banking
Net interest income:
Net interest income	$ 196,803	209,912	$ 609,316	635,645
Net interest income, Change in Contribution	$ (13,109)		$ (26,329)
Net interest income, Change in Contribution (as a percent)	(6.00%)		(4.00%)
Non-interest income:
Non-interest income	$ 136,996	82,870	$ 347,697	196,507
Non-interest income, Change in Contribution	$ 54,126		$ 151,190
Non-interest income, Change in Contribution (as a percent)	65.00%		77.00%
Net revenue:
Net revenue	$ 333,799	292,782	$ 957,013	832,152
Net revenue, Change in Contribution	$ 41,017		$ 124,861
Net revenue, Change in Contribution (as a percent)	14.00%		15.00%
Operating Segments | Specialty finance
Net interest income:
Net interest income	$ 46,454	42,138	$ 129,581	119,241
Net interest income, Change in Contribution	$ 4,316		$ 10,340
Net interest income, Change in Contribution (as a percent)	10.00%		9.00%
Non-interest income:
Non-interest income	$ 21,409	20,003	$ 64,548	59,188
Non-interest income, Change in Contribution	$ 1,406		$ 5,360
Non-interest income, Change in Contribution (as a percent)	7.00%		9.00%
Net revenue:
Net revenue	$ 67,863	62,141	$ 194,129	178,429
Net revenue, Change in Contribution	$ 5,722		$ 15,700
Net revenue, Change in Contribution (as a percent)	9.00%		9.00%
Operating Segments | Wealth management
Net interest income:
Net interest income	$ 6,894	7,290	$ 23,272	21,728
Net interest income, Change in Contribution	$ (396)		$ 1,544
Net interest income, Change in Contribution (as a percent)	(5.00%)		7.00%
Non-interest income:
Non-interest income	$ 26,152	24,422	$ 74,747	74,407
Non-interest income, Change in Contribution	$ 1,730		$ 340
Non-interest income, Change in Contribution (as a percent)	7.00%		0.00%
Net revenue:
Net revenue	$ 33,046	31,712	$ 98,019	96,135
Net revenue, Change in Contribution	$ 1,334		$ 1,884
Net revenue, Change in Contribution (as a percent)	4.00%		2.00%
Intersegment Eliminations
Net interest income:
Net interest income	$ 5,785	5,512	$ 18,341	16,426
Net interest income, Change in Contribution	$ 273		$ 1,915
Net interest income, Change in Contribution (as a percent)	5.00%		12.00%
Non-interest income:
Non-interest income	$ (13,964)	(12,158)	$ (41,164)	(35,150)
Non-interest income, Change in Contribution	$ (1,806)		$ (6,014)
Non-interest income, Change in Contribution (as a percent)	15.00%		17.00%
Net revenue:
Net revenue	$ (8,179)	$ (6,646)	$ (22,823)	$ (18,724)
Net revenue, Change in Contribution	$ (1,533)		$ (4,099)
Net revenue, Change in Contribution (as a percent)	23.00%		22.00%