Segment Information (Summary of Segment Information) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net interest income	$ 175,270	$ 156,892	$ 346,779	$ 308,783
Net interest income, Change in Contribution	$ 18,378		$ 37,996
Net interest income, Change in Contribution Percentage	12.00%		12.00%
Non-interest income	$ 84,799	77,013	$ 153,551	141,554
Non-interest income, Change in Contribution	$ 7,786		$ 11,997
Non-interest income, Change in Contribution Percentage	10.00%		8.00%
Net revenue	$ 260,069	233,905	$ 500,330	450,337
Net revenue, Change in Contribution	$ 26,164		$ 49,993
Net revenue, Change in Contribution Percentage	11.00%		11.00%
Segment profit	$ 50,041	43,831	$ 99,152	82,883
Segment profit, Change in Contribution	$ 6,210		$ 16,269
Segment profit, Change in Contribution Percentage	14.00%		20.00%
Segment assets	$ 24,420,616	20,790,202	$ 24,420,616	20,790,202	$ 22,909,348
Segment assets, Change in Contribution	$ 3,630,414
Segment assets, Change in Contribution Percentage	17.00%
Operating Segments
Segment Reporting Information [Line Items]
Net interest income	$ 170,986	152,582	338,347	300,498
Net interest income, Change in Contribution	$ 18,404		$ 37,849
Net interest income, Change in Contribution Percentage	12.00%		13.00%
Non-interest income	$ 93,158	84,401	$ 169,980	155,912
Non-interest income, Change in Contribution	$ 8,757		$ 14,068
Non-interest income, Change in Contribution Percentage	10.00%		9.00%
Net revenue	$ 264,144	236,983	$ 508,327	456,410
Net revenue, Change in Contribution	$ 27,161		$ 51,917
Net revenue, Change in Contribution Percentage	11.00%		11.00%
Operating Segments | Community banking
Segment Reporting Information [Line Items]
Net interest income	$ 142,251	126,964	$ 283,949	249,645
Net interest income, Change in Contribution	$ 15,287		$ 34,304
Net interest income, Change in Contribution Percentage	12.00%		14.00%
Non-interest income	$ 60,813	56,253	$ 106,480	101,165
Non-interest income, Change in Contribution	$ 4,560		$ 5,315
Non-interest income, Change in Contribution Percentage	8.00%		5.00%
Net revenue	$ 203,064	183,217	$ 390,429	350,810
Net revenue, Change in Contribution	$ 19,847		$ 39,619
Net revenue, Change in Contribution Percentage	11.00%		11.00%
Segment profit	$ 34,576	29,133	$ 69,333	54,098
Segment profit, Change in Contribution	$ 5,443		$ 15,235
Segment profit, Change in Contribution Percentage	19.00%		28.00%
Segment assets	$ 20,190,707	17,312,377	$ 20,190,707	17,312,377
Segment assets, Change in Contribution	$ 2,878,330
Segment assets, Change in Contribution Percentage	17.00%
Operating Segments | Specialty finance
Segment Reporting Information [Line Items]
Net interest income	$ 24,352	21,338	45,532	42,384
Net interest income, Change in Contribution	$ 3,014		$ 3,148
Net interest income, Change in Contribution Percentage	14.00%		7.00%
Non-interest income	$ 12,482	9,135	$ 24,885	17,006
Non-interest income, Change in Contribution	$ 3,347		$ 7,879
Non-interest income, Change in Contribution Percentage	37.00%		46.00%
Net revenue	$ 36,834	30,473	$ 70,417	59,390
Net revenue, Change in Contribution	$ 6,361		$ 11,027
Net revenue, Change in Contribution Percentage	21.00%		19.00%
Segment profit	$ 12,044	11,378	$ 23,516	22,330
Segment profit, Change in Contribution	$ 666		$ 1,186
Segment profit, Change in Contribution Percentage	6.00%		5.00%
Segment assets	$ 3,645,077	2,931,838	$ 3,645,077	2,931,838
Segment assets, Change in Contribution	$ 713,239
Segment assets, Change in Contribution Percentage	24.00%
Operating Segments | Wealth management
Segment Reporting Information [Line Items]
Net interest income	$ 4,383	4,280	8,866	8,469
Net interest income, Change in Contribution	$ 103		$ 397
Net interest income, Change in Contribution Percentage	2.00%		5.00%
Non-interest income	$ 19,863	19,013	$ 38,615	37,741
Non-interest income, Change in Contribution	$ 850		$ 874
Non-interest income, Change in Contribution Percentage	4.00%		2.00%
Net revenue	$ 24,246	23,293	$ 47,481	46,210
Net revenue, Change in Contribution	$ 953		$ 1,271
Net revenue, Change in Contribution Percentage	4.00%		3.00%
Segment profit	$ 3,421	3,320	$ 6,303	6,455
Segment profit, Change in Contribution	$ 101		$ (152)
Segment profit, Change in Contribution Percentage	3.00%		(2.00%)
Segment assets	$ 584,832	545,987	$ 584,832	545,987
Segment assets, Change in Contribution	$ 38,845
Segment assets, Change in Contribution Percentage	7.00%
Intersegment Eliminations
Segment Reporting Information [Line Items]
Net interest income	$ 4,284	4,310	8,432	8,285
Net interest income, Change in Contribution	$ (26)		$ 147
Net interest income, Change in Contribution Percentage	(1.00%)		2.00%
Non-interest income	$ (8,359)	(7,388)	$ (16,429)	(14,358)
Non-interest income, Change in Contribution	$ (971)		$ (2,071)
Non-interest income, Change in Contribution Percentage	(13.00%)		(14.00%)
Net revenue	$ (4,075)	$ (3,078)	$ (7,997)	$ (6,073)
Net revenue, Change in Contribution	$ (997)		$ (1,924)
Net revenue, Change in Contribution Percentage	(32.00%)		(32.00%)