Segment Information (Summary of Segment Information) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net interest income	$ 184,636	$ 165,540	$ 531,415	$ 474,323
Net interest income, Change in Contribution	$ 19,096		$ 57,092
Net interest income, Change in Contribution Percentage	12.00%		12.00%
Non-interest income	$ 86,604	64,953	$ 240,155	206,507
Non-interest income, Change in Contribution	$ 21,651		$ 33,648
Non-interest income, Change in Contribution Percentage	33.00%		16.00%
Net revenue	$ 271,240	230,493	$ 771,570	680,830
Net revenue, Change in Contribution	$ 40,747		$ 90,740
Net revenue, Change in Contribution Percentage	18.00%		13.00%
Segment profit	$ 53,115	38,355	$ 152,267	121,238
Segment profit, Change in Contribution	$ 14,760		$ 31,029
Segment profit, Change in Contribution Percentage	38.00%		26.00%
Segment assets	$ 25,321,759	22,035,216	$ 25,321,759	22,035,216	$ 22,909,348
Segment assets, Change in Contribution	$ 3,286,543
Segment assets, Change in Contribution Percentage	15.00%
Operating Segments
Segment Reporting Information [Line Items]
Net interest income	$ 180,537	161,567	518,884	462,065
Net interest income, Change in Contribution	$ 18,970		$ 56,819
Net interest income, Change in Contribution Percentage	12.00%		12.00%
Non-interest income	$ 95,001	72,200	$ 264,981	228,112
Non-interest income, Change in Contribution	$ 22,801		$ 36,869
Non-interest income, Change in Contribution Percentage	32.00%		16.00%
Net revenue	$ 275,538	233,767	$ 783,865	690,177
Net revenue, Change in Contribution	$ 41,771		$ 93,688
Net revenue, Change in Contribution Percentage	18.00%		14.00%
Operating Segments | Community banking
Segment Reporting Information [Line Items]
Net interest income	$ 150,159	132,542	$ 434,108	382,187
Net interest income, Change in Contribution	$ 17,617		$ 51,921
Net interest income, Change in Contribution Percentage	13.00%		14.00%
Non-interest income	$ 62,730	45,574	$ 169,210	146,739
Non-interest income, Change in Contribution	$ 17,156		$ 22,471
Non-interest income, Change in Contribution Percentage	38.00%		15.00%
Net revenue	$ 212,889	178,116	$ 603,318	528,926
Net revenue, Change in Contribution	$ 34,773		$ 74,392
Net revenue, Change in Contribution Percentage	20.00%		14.00%
Segment profit	$ 37,527	22,723	$ 106,860	76,821
Segment profit, Change in Contribution	$ 14,804		$ 30,039
Segment profit, Change in Contribution Percentage	65.00%		39.00%
Segment assets	$ 21,019,002	18,497,364	$ 21,019,002	18,497,364
Segment assets, Change in Contribution	$ 2,521,638
Segment assets, Change in Contribution Percentage	14.00%
Operating Segments | Specialty finance
Segment Reporting Information [Line Items]
Net interest income	$ 25,543	24,657	71,075	67,041
Net interest income, Change in Contribution	$ 886		$ 4,034
Net interest income, Change in Contribution Percentage	4.00%		6.00%
Non-interest income	$ 12,226	8,264	$ 37,111	25,270
Non-interest income, Change in Contribution	$ 3,962		$ 11,841
Non-interest income, Change in Contribution Percentage	48.00%		47.00%
Net revenue	$ 37,769	32,921	$ 108,186	92,311
Net revenue, Change in Contribution	$ 4,848		$ 15,875
Net revenue, Change in Contribution Percentage	15.00%		17.00%
Segment profit	$ 12,767	12,545	$ 36,283	34,875
Segment profit, Change in Contribution	$ 222		$ 1,408
Segment profit, Change in Contribution Percentage	2.00%		4.00%
Segment assets	$ 3,702,241	2,987,021	$ 3,702,241	2,987,021
Segment assets, Change in Contribution	$ 715,220
Segment assets, Change in Contribution Percentage	24.00%
Operating Segments | Wealth management
Segment Reporting Information [Line Items]
Net interest income	$ 4,835	4,368	13,701	12,837
Net interest income, Change in Contribution	$ 467		$ 864
Net interest income, Change in Contribution Percentage	11.00%		7.00%
Non-interest income	$ 20,045	18,362	$ 58,660	56,103
Non-interest income, Change in Contribution	$ 1,683		$ 2,557
Non-interest income, Change in Contribution Percentage	9.00%		5.00%
Net revenue	$ 24,880	22,730	$ 72,361	68,940
Net revenue, Change in Contribution	$ 2,150		$ 3,421
Net revenue, Change in Contribution Percentage	9.00%		5.00%
Segment profit	$ 2,821	3,087	$ 9,124	9,542
Segment profit, Change in Contribution	$ (266)		$ (418)
Segment profit, Change in Contribution Percentage	(9.00%)		(4.00%)
Segment assets	$ 600,516	550,831	$ 600,516	550,831
Segment assets, Change in Contribution	$ 49,685
Segment assets, Change in Contribution Percentage	9.00%
Intersegment Eliminations
Segment Reporting Information [Line Items]
Net interest income	$ 4,099	3,973	12,531	12,258
Net interest income, Change in Contribution	$ 126		$ 273
Net interest income, Change in Contribution Percentage	3.00%		2.00%
Non-interest income	$ (8,397)	(7,247)	$ (24,826)	(21,605)
Non-interest income, Change in Contribution	$ (1,150)		$ (3,221)
Non-interest income, Change in Contribution Percentage	(16.00%)		(15.00%)
Net revenue	$ (4,298)	$ (3,274)	$ (12,295)	$ (9,347)
Net revenue, Change in Contribution	$ (1,024)		$ (2,948)
Net revenue, Change in Contribution Percentage	(31.00%)		(32.00%)