Segment Information (Summary of Segment Information) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Net interest income:
Net interest income	$ 261,986	$ 225,082
Net interest income, Change in Contribution	$ 36,904
Net interest income, Change in Contribution (as a percent)	16.00%
Non-interest income:
Non-interest income	$ 81,657	85,679
Non-interest income, Change in Contribution	$ (4,022)
Non-interest income, Change in Contribution (as a percent)	(5.00%)
Net revenue:
Net revenue	$ 343,643	310,761
Net revenue, Change in Contribution	$ 32,882
Net revenue, Change in Contribution (as a percent)	11.00%
Segment profit:
Segment profit	$ 89,146	81,981
Segment profit, Change in Contribution	$ 7,165
Segment profit, Change in Contribution (as a percent)	9.00%
Segment assets:
Segment assets	$ 32,358,621	28,456,772	$ 31,244,849
Segment assets, Change in Contribution	$ 3,901,849
Segment assets, Change in Contribution (as a percent)	14.00%
Community banking
Segment profit:
Segment profit	$ 60,326	57,280
Segment profit, Change in Contribution	$ 3,046
Segment profit, Change in Contribution (as a percent)	5.00%
Segment assets:
Segment assets	$ 25,997,025	23,213,499
Segment assets, Change in Contribution	$ 2,783,526
Segment assets, Change in Contribution (as a percent)	12.00%
Specialty finance
Segment profit:
Segment profit	$ 21,848	20,000
Segment profit, Change in Contribution	$ 1,848
Segment profit, Change in Contribution (as a percent)	9.00%
Segment assets:
Segment assets	$ 5,234,210	4,568,906
Segment assets, Change in Contribution	$ 665,304
Segment assets, Change in Contribution (as a percent)	15.00%
Wealth management
Segment profit:
Segment profit	$ 6,972	4,701
Segment profit, Change in Contribution	$ 2,271
Segment profit, Change in Contribution (as a percent)	48.00%
Segment assets:
Segment assets	$ 1,127,386	674,367
Segment assets, Change in Contribution	$ 453,019
Segment assets, Change in Contribution (as a percent)	67.00%
Operating Segments
Net interest income:
Net interest income	$ 256,632	220,607
Net interest income, Change in Contribution	$ 36,025
Net interest income, Change in Contribution (as a percent)	16.00%
Non-interest income:
Non-interest income	$ 92,908	95,230
Non-interest income, Change in Contribution	$ (2,322)
Non-interest income, Change in Contribution (as a percent)	(2.00%)
Net revenue:
Net revenue	$ 349,540	315,837
Net revenue, Change in Contribution	$ 33,703
Net revenue, Change in Contribution (as a percent)	11.00%
Operating Segments | Community banking
Net interest income:
Net interest income	$ 211,424	183,254
Net interest income, Change in Contribution	$ 28,170
Net interest income, Change in Contribution (as a percent)	15.00%
Non-interest income:
Non-interest income	$ 48,267	56,547
Non-interest income, Change in Contribution	$ (8,280)
Non-interest income, Change in Contribution (as a percent)	(15.00%)
Net revenue:
Net revenue	$ 259,691	239,801
Net revenue, Change in Contribution	$ 19,890
Net revenue, Change in Contribution (as a percent)	8.00%
Operating Segments | Specialty finance
Net interest income:
Net interest income	$ 37,706	32,912
Net interest income, Change in Contribution	$ 4,794
Net interest income, Change in Contribution (as a percent)	15.00%
Non-interest income:
Non-interest income	$ 19,606	15,725
Non-interest income, Change in Contribution	$ 3,881
Non-interest income, Change in Contribution (as a percent)	25.00%
Net revenue:
Net revenue	$ 57,312	48,637
Net revenue, Change in Contribution	$ 8,675
Net revenue, Change in Contribution (as a percent)	18.00%
Operating Segments | Wealth management
Net interest income:
Net interest income	$ 7,502	4,441
Net interest income, Change in Contribution	$ 3,061
Net interest income, Change in Contribution (as a percent)	69.00%
Non-interest income:
Non-interest income	$ 25,035	22,958
Non-interest income, Change in Contribution	$ 2,077
Non-interest income, Change in Contribution (as a percent)	9.00%
Net revenue:
Net revenue	$ 32,537	27,399
Net revenue, Change in Contribution	$ 5,138
Net revenue, Change in Contribution (as a percent)	19.00%
Intersegment Eliminations
Net interest income:
Net interest income	$ 5,354	4,475
Net interest income, Change in Contribution	$ 879
Net interest income, Change in Contribution (as a percent)	20.00%
Non-interest income:
Non-interest income	$ (11,251)	(9,551)
Non-interest income, Change in Contribution	$ (1,700)
Non-interest income, Change in Contribution (as a percent)	(18.00%)
Net revenue:
Net revenue	$ (5,897)	$ (5,076)
Net revenue, Change in Contribution	$ (821)
Net revenue, Change in Contribution (as a percent)	(16.00%)