Segment Information (Summary of Segment Information) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Net interest income	$ 156,892	$ 149,180	$ 308,783	$ 293,186
Net interest income, Change in Contribution	$ 7,712		$ 15,597
Net interest income, Change in Contribution Percentage	5.00%		5.00%
Non-interest income	$ 77,013	54,102	$ 141,554	99,631
Non-interest income, Change in Contribution	$ 22,911		$ 41,923
Non-interest income, Change in Contribution Percentage	42.00%		42.00%
Net revenue	$ 233,905	203,282	$ 450,337	392,817
Net revenue, Change in Contribution	$ 30,623		$ 57,520
Net revenue, Change in Contribution Percentage	15.00%		15.00%
Segment profit	$ 43,831	38,541	$ 82,883	73,041
Segment profit, Change in Contribution	$ 5,290		$ 9,842
Segment profit, Change in Contribution Percentage	14.00%		13.00%
Segment assets	$ 20,799,924	18,895,681	$ 20,799,924	18,895,681	$ 20,010,727
Segment assets, Change in Contribution	$ 1,904,243
Segment assets, Change in Contribution Percentage	10.00%
Operating Segments
Segment Reporting Information [Line Items]
Net interest income	$ 152,582	145,026	300,498	285,092
Net interest income, Change in Contribution	$ 7,556		$ 15,406
Net interest income, Change in Contribution Percentage	5.00%		5.00%
Non-interest income	$ 84,401	61,027	$ 155,912	113,168
Non-interest income, Change in Contribution	$ 23,374		$ 42,744
Non-interest income, Change in Contribution Percentage	38.00%		38.00%
Net revenue	$ 236,983	206,053	$ 456,410	398,260
Net revenue, Change in Contribution	$ 30,930		$ 58,150
Net revenue, Change in Contribution Percentage	15.00%		15.00%
Operating Segments | Community banking
Segment Reporting Information [Line Items]
Net interest income	$ 126,964	121,228	$ 249,645	237,983
Net interest income, Change in Contribution	$ 5,736		$ 11,662
Net interest income, Change in Contribution Percentage	5.00%		5.00%
Non-interest income	$ 56,253	33,337	$ 101,165	60,656
Non-interest income, Change in Contribution	$ 22,916		$ 40,509
Non-interest income, Change in Contribution Percentage	69.00%		67.00%
Net revenue	$ 183,217	154,565	$ 350,810	298,639
Net revenue, Change in Contribution	$ 28,652		$ 52,171
Net revenue, Change in Contribution Percentage	19.00%		17.00%
Segment profit	$ 29,133	24,628	$ 54,098	47,209
Segment profit, Change in Contribution	$ 4,505		$ 6,889
Segment profit, Change in Contribution Percentage	18.00%		15.00%
Segment assets	$ 17,321,956	15,669,443	$ 17,321,956	15,669,443
Segment assets, Change in Contribution	$ 1,652,513
Segment assets, Change in Contribution Percentage	11.00%
Operating Segments | Specialty finance
Segment Reporting Information [Line Items]
Net interest income	$ 21,338	19,792	42,384	39,004
Net interest income, Change in Contribution	$ 1,546		$ 3,380
Net interest income, Change in Contribution Percentage	8.00%		9.00%
Non-interest income	$ 9,135	8,455	$ 17,006	16,336
Non-interest income, Change in Contribution	$ 680		$ 670
Non-interest income, Change in Contribution Percentage	8.00%		4.00%
Net revenue	$ 30,473	28,247	$ 59,390	55,340
Net revenue, Change in Contribution	$ 2,226		$ 4,050
Net revenue, Change in Contribution Percentage	8.00%		7.00%
Segment profit	$ 11,378	10,302	$ 22,330	19,284
Segment profit, Change in Contribution	$ 1,076		$ 3,046
Segment profit, Change in Contribution Percentage	10.00%		16.00%
Segment assets	$ 2,931,975	2,703,761	$ 2,931,975	2,703,761
Segment assets, Change in Contribution	$ 228,214
Segment assets, Change in Contribution Percentage	8.00%
Operating Segments | Wealth management
Segment Reporting Information [Line Items]
Net interest income	$ 4,280	4,006	8,469	8,105
Net interest income, Change in Contribution	$ 274		$ 364
Net interest income, Change in Contribution Percentage	7.00%		4.00%
Non-interest income	$ 19,013	19,235	$ 37,741	36,176
Non-interest income, Change in Contribution	$ (222)		$ 1,565
Non-interest income, Change in Contribution Percentage	(1.00%)		4.00%
Net revenue	$ 23,293	23,241	$ 46,210	44,281
Net revenue, Change in Contribution	$ 52		$ 1,929
Net revenue, Change in Contribution Percentage	0.00%		4.00%
Segment profit	$ 3,320	3,611	$ 6,455	6,548
Segment profit, Change in Contribution	$ (291)		$ (93)
Segment profit, Change in Contribution Percentage	(8.00%)		(1.00%)
Segment assets	$ 545,993	522,477	$ 545,993	522,477
Segment assets, Change in Contribution	$ 23,516
Segment assets, Change in Contribution Percentage	5.00%
Intersegment Eliminations
Segment Reporting Information [Line Items]
Net interest income	$ 4,310	4,154	8,285	8,094
Net interest income, Change in Contribution	$ 156		$ 191
Net interest income, Change in Contribution Percentage	4.00%		2.00%
Non-interest income	$ (7,388)	(6,925)	$ (14,358)	(13,537)
Non-interest income, Change in Contribution	$ (463)		$ (821)
Non-interest income, Change in Contribution Percentage	(7.00%)		(6.00%)
Net revenue	$ (3,078)	$ (2,771)	$ (6,073)	$ (5,443)
Net revenue, Change in Contribution	$ (307)		$ (630)
Net revenue, Change in Contribution Percentage	(11.00%)		(12.00%)