Segment Information (Summary of Segment Information) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Net interest income:
Net interest income	$ 261,443	$ 261,986
Net interest income, Change in Contribution	$ (543)
Net interest income, Change in Contribution (as a percent)	0.00%
Non-interest income:
Non-interest income	$ 113,242	81,657
Non-interest income, Change in Contribution	$ 31,585
Non-interest income, Change in Contribution (as a percent)	39.00%
Net revenue:
Net revenue	$ 374,685	343,643
Net revenue, Change in Contribution	$ 31,042
Net revenue, Change in Contribution (as a percent)	9.00%
Segment profit:
Segment profit	$ 62,812	89,146
Segment profit, Change in Contribution	$ (26,334)
Segment profit, Change in Contribution (as a percent)	(30.00%)
Segment assets:
Segment assets	$ 38,799,847	32,358,621	$ 36,620,583
Segment assets, Change in Contribution	$ 6,441,226
Segment assets, Change in Contribution (as a percent)	20.00%
Community banking
Segment profit:
Segment profit	$ 34,589	60,326
Segment profit, Change in Contribution	$ (25,737)
Segment profit, Change in Contribution (as a percent)	(43.00%)
Segment assets:
Segment assets	$ 31,499,899	25,997,025
Segment assets, Change in Contribution	$ 5,502,874
Segment assets, Change in Contribution (as a percent)	21.00%
Specialty finance
Segment profit:
Segment profit	$ 22,133	21,848
Segment profit, Change in Contribution	$ 285
Segment profit, Change in Contribution (as a percent)	1.00%
Segment assets:
Segment assets	$ 6,133,548	5,234,210
Segment assets, Change in Contribution	$ 899,338
Segment assets, Change in Contribution (as a percent)	17.00%
Wealth management
Segment profit:
Segment profit	$ 6,090	6,972
Segment profit, Change in Contribution	$ (882)
Segment profit, Change in Contribution (as a percent)	(13.00%)
Segment assets:
Segment assets	$ 1,166,400	1,127,386
Segment assets, Change in Contribution	$ 39,014
Segment assets, Change in Contribution (as a percent)	3.00%
Operating Segments
Net interest income:
Net interest income	$ 255,339	256,632
Net interest income, Change in Contribution	$ (1,293)
Net interest income, Change in Contribution (as a percent)	(1.00%)
Non-interest income:
Non-interest income	$ 126,441	92,908
Non-interest income, Change in Contribution	$ 33,533
Non-interest income, Change in Contribution (as a percent)	36.00%
Net revenue:
Net revenue	$ 381,780	349,540
Net revenue, Change in Contribution	$ 32,240
Net revenue, Change in Contribution (as a percent)	9.00%
Operating Segments | Community banking
Net interest income:
Net interest income	$ 206,835	211,424
Net interest income, Change in Contribution	$ (4,589)
Net interest income, Change in Contribution (as a percent)	(2.00%)
Non-interest income:
Non-interest income	$ 81,003	48,267
Non-interest income, Change in Contribution	$ 32,736
Non-interest income, Change in Contribution (as a percent)	68.00%
Net revenue:
Net revenue	$ 287,838	259,691
Net revenue, Change in Contribution	$ 28,147
Net revenue, Change in Contribution (as a percent)	11.00%
Operating Segments | Specialty finance
Net interest income:
Net interest income	$ 40,712	37,706
Net interest income, Change in Contribution	$ 3,006
Net interest income, Change in Contribution (as a percent)	8.00%
Non-interest income:
Non-interest income	$ 21,308	19,606
Non-interest income, Change in Contribution	$ 1,702
Non-interest income, Change in Contribution (as a percent)	9.00%
Net revenue:
Net revenue	$ 62,020	57,312
Net revenue, Change in Contribution	$ 4,708
Net revenue, Change in Contribution (as a percent)	8.00%
Operating Segments | Wealth management
Net interest income:
Net interest income	$ 7,792	7,502
Net interest income, Change in Contribution	$ 290
Net interest income, Change in Contribution (as a percent)	4.00%
Non-interest income:
Non-interest income	$ 24,130	25,035
Non-interest income, Change in Contribution	$ (905)
Non-interest income, Change in Contribution (as a percent)	(4.00%)
Net revenue:
Net revenue	$ 31,922	32,537
Net revenue, Change in Contribution	$ (615)
Net revenue, Change in Contribution (as a percent)	(2.00%)
Intersegment Eliminations
Net interest income:
Net interest income	$ 6,104	5,354
Net interest income, Change in Contribution	$ 750
Net interest income, Change in Contribution (as a percent)	14.00%
Non-interest income:
Non-interest income	$ (13,199)	(11,251)
Non-interest income, Change in Contribution	$ (1,948)
Non-interest income, Change in Contribution (as a percent)	(17.00%)
Net revenue:
Net revenue	$ (7,095)	$ (5,897)
Net revenue, Change in Contribution	$ (1,198)
Net revenue, Change in Contribution (as a percent)	(20.00%)