Segment Information (Summary of Segment Information) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Net interest income:
Net interest income	$ 263,131	$ 266,202	$ 524,574	$ 528,188
Net interest income, Change in Contribution	$ (3,071)		$ (3,614)
Net interest income, Change in Contribution (as a percent)	(1.00%)		(1.00%)
Non-interest income:
Non-interest income	$ 161,993	98,158	$ 275,235	179,815
Non-interest income, Change in Contribution	$ 63,835		$ 95,420
Non-interest income, Change in Contribution (as a percent)	65.00%		53.00%
Net revenue:
Net revenue	$ 425,124	364,360	$ 799,809	708,003
Net revenue, Change in Contribution	$ 60,764		$ 91,806
Net revenue, Change in Contribution (as a percent)	17.00%		13.00%
Segment (loss) profit:
Segment profit	$ 21,659	81,466	$ 84,471	170,612
Segment profit, Change in Contribution	$ (59,807)		$ (86,141)
Segment profit, Change in Contribution (as a percent)	(73.00%)		(50.00%)
Segment assets:
Segment assets	$ 43,540,017	33,641,769	$ 43,540,017	33,641,769	$ 36,620,583
Segment assets, Change in Contribution	$ 9,898,248
Segment assets, Change in Contribution (as a percent)	29.00%
Community banking
Segment (loss) profit:
Segment profit	$ (7,315)	53,435	27,274	113,761
Segment profit, Change in Contribution	$ (60,750)		$ (86,487)
Segment profit, Change in Contribution (as a percent)	(114.00%)		(76.00%)
Segment assets:
Segment assets	$ 35,560,107	27,005,555	$ 35,560,107	27,005,555
Segment assets, Change in Contribution	$ 8,554,552
Segment assets, Change in Contribution (as a percent)	32.00%
Specialty finance
Segment (loss) profit:
Segment profit	$ 22,688	21,129	44,821	42,977
Segment profit, Change in Contribution	$ 1,559		$ 1,844
Segment profit, Change in Contribution (as a percent)	7.00%		4.00%
Segment assets:
Segment assets	$ 6,708,493	5,566,067	$ 6,708,493	5,566,067
Segment assets, Change in Contribution	$ 1,142,426
Segment assets, Change in Contribution (as a percent)	21.00%
Wealth management
Segment (loss) profit:
Segment profit	$ 6,286	6,902	12,376	13,874
Segment profit, Change in Contribution	$ (616)		$ (1,498)
Segment profit, Change in Contribution (as a percent)	(9.00%)		(11.00%)
Segment assets:
Segment assets	$ 1,271,417	1,070,147	$ 1,271,417	1,070,147
Segment assets, Change in Contribution	$ 201,270
Segment assets, Change in Contribution (as a percent)	19.00%
Operating Segments
Net interest income:
Net interest income	$ 256,679	260,642	512,018	517,274
Net interest income, Change in Contribution	$ (3,963)		$ (5,256)
Net interest income, Change in Contribution (as a percent)	(2.00%)		(1.00%)
Non-interest income:
Non-interest income	$ 175,994	109,899	$ 302,435	202,807
Non-interest income, Change in Contribution	$ 66,095		$ 99,628
Non-interest income, Change in Contribution (as a percent)	60.00%		49.00%
Net revenue:
Net revenue	$ 432,673	370,541	$ 814,453	720,081
Net revenue, Change in Contribution	$ 62,132		$ 94,372
Net revenue, Change in Contribution (as a percent)	17.00%		13.00%
Operating Segments | Community banking
Net interest income:
Net interest income	$ 205,678	214,309	$ 412,513	425,733
Net interest income, Change in Contribution	$ (8,631)		$ (13,220)
Net interest income, Change in Contribution (as a percent)	(4.00%)		(3.00%)
Non-interest income:
Non-interest income	$ 129,698	65,370	$ 210,701	113,637
Non-interest income, Change in Contribution	$ 64,328		$ 97,064
Non-interest income, Change in Contribution (as a percent)	98.00%		85.00%
Net revenue:
Net revenue	$ 335,376	279,679	$ 623,214	539,370
Net revenue, Change in Contribution	$ 55,697		$ 83,844
Net revenue, Change in Contribution (as a percent)	20.00%		16.00%
Operating Segments | Specialty finance
Net interest income:
Net interest income	$ 42,415	39,397	$ 83,127	77,103
Net interest income, Change in Contribution	$ 3,018		$ 6,024
Net interest income, Change in Contribution (as a percent)	8.00%		8.00%
Non-interest income:
Non-interest income	$ 21,831	19,579	$ 43,139	39,185
Non-interest income, Change in Contribution	$ 2,252		$ 3,954
Non-interest income, Change in Contribution (as a percent)	12.00%		10.00%
Net revenue:
Net revenue	$ 64,246	58,976	$ 126,266	116,288
Net revenue, Change in Contribution	$ 5,270		$ 9,978
Net revenue, Change in Contribution (as a percent)	9.00%		9.00%
Operating Segments | Wealth management
Net interest income:
Net interest income	$ 8,586	6,936	$ 16,378	14,438
Net interest income, Change in Contribution	$ 1,650		$ 1,940
Net interest income, Change in Contribution (as a percent)	24.00%		13.00%
Non-interest income:
Non-interest income	$ 24,465	24,950	$ 48,595	49,985
Non-interest income, Change in Contribution	$ (485)		$ (1,390)
Non-interest income, Change in Contribution (as a percent)	(2.00%)		(3.00%)
Net revenue:
Net revenue	$ 33,051	31,886	$ 64,973	64,423
Net revenue, Change in Contribution	$ 1,165		$ 550
Net revenue, Change in Contribution (as a percent)	4.00%		1.00%
Intersegment Eliminations
Net interest income:
Net interest income	$ 6,452	5,560	$ 12,556	10,914
Net interest income, Change in Contribution	$ 892		$ 1,642
Net interest income, Change in Contribution (as a percent)	16.00%		15.00%
Non-interest income:
Non-interest income	$ (14,001)	(11,741)	$ (27,200)	(22,992)
Non-interest income, Change in Contribution	$ (2,260)		$ (4,208)
Non-interest income, Change in Contribution (as a percent)	(19.00%)		18.00%
Net revenue:
Net revenue	$ (7,549)	$ (6,181)	$ (14,644)	$ (12,078)
Net revenue, Change in Contribution	$ (1,368)		$ (2,566)
Net revenue, Change in Contribution (as a percent)	(22.00%)		21.00%