Segment Information (Summary of Segment Information) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Net interest income	$ 165,540	$ 151,670	$ 474,323	$ 444,856
Net interest income, Change in Contribution	$ 13,870		$ 29,467
Net interest income, Change in Contribution Percentage	9.00%		7.00%
Non-interest income	$ 64,953	57,952	$ 206,507	157,583
Non-interest income, Change in Contribution	$ 7,001		$ 48,924
Non-interest income, Change in Contribution Percentage	12.00%		31.00%
Net revenue	$ 230,493	209,622	$ 680,830	602,439
Net revenue, Change in Contribution	$ 20,871		$ 78,391
Net revenue, Change in Contribution Percentage	10.00%		13.00%
Segment profit	$ 38,355	40,224	$ 121,238	113,265
Segment profit, Change in Contribution	$ (1,869)		$ 7,973
Segment profit, Change in Contribution Percentage	(5.00%)		7.00%
Segment assets	$ 22,043,930	19,169,345	$ 22,043,930	19,169,345	$ 20,010,727
Segment assets, Change in Contribution	$ 2,874,585
Segment assets, Change in Contribution Percentage	15.00%
Operating Segments
Segment Reporting Information [Line Items]
Net interest income	$ 161,567	147,778	462,065	432,870
Net interest income, Change in Contribution	$ 13,789		$ 29,195
Net interest income, Change in Contribution Percentage	9.00%		7.00%
Non-interest income	$ 72,200	64,785	$ 228,112	177,953
Non-interest income, Change in Contribution	$ 7,415		$ 50,159
Non-interest income, Change in Contribution Percentage	11.00%		28.00%
Net revenue	$ 233,767	212,563	$ 690,177	610,823
Net revenue, Change in Contribution	$ 21,204		$ 79,354
Net revenue, Change in Contribution Percentage	10.00%		13.00%
Operating Segments | Community banking
Segment Reporting Information [Line Items]
Net interest income	$ 132,542	121,998	$ 382,187	359,981
Net interest income, Change in Contribution	$ 10,544		$ 22,206
Net interest income, Change in Contribution Percentage	9.00%		6.00%
Non-interest income	$ 45,574	38,274	$ 146,739	98,930
Non-interest income, Change in Contribution	$ 7,300		$ 47,809
Non-interest income, Change in Contribution Percentage	19.00%		48.00%
Net revenue	$ 178,116	160,272	$ 528,926	458,911
Net revenue, Change in Contribution	$ 17,844		$ 70,015
Net revenue, Change in Contribution Percentage	11.00%		15.00%
Segment profit	$ 22,723	26,184	$ 76,821	73,393
Segment profit, Change in Contribution	$ (3,461)		$ 3,428
Segment profit, Change in Contribution Percentage	(13.00%)		5.00%
Segment assets	$ 18,505,830	15,945,744	$ 18,505,830	15,945,744
Segment assets, Change in Contribution	$ 2,560,086
Segment assets, Change in Contribution Percentage	16.00%
Operating Segments | Specialty finance
Segment Reporting Information [Line Items]
Net interest income	$ 24,657	21,903	67,041	60,907
Net interest income, Change in Contribution	$ 2,754		$ 6,134
Net interest income, Change in Contribution Percentage	13.00%		10.00%
Non-interest income	$ 8,264	8,320	$ 25,270	24,656
Non-interest income, Change in Contribution	$ (56)		$ 614
Non-interest income, Change in Contribution Percentage	(1.00%)		2.00%
Net revenue	$ 32,921	30,223	$ 92,311	85,563
Net revenue, Change in Contribution	$ 2,698		$ 6,748
Net revenue, Change in Contribution Percentage	9.00%		8.00%
Segment profit	$ 12,545	10,973	$ 34,875	30,257
Segment profit, Change in Contribution	$ 1,572		$ 4,618
Segment profit, Change in Contribution Percentage	14.00%		15.00%
Segment assets	$ 2,987,236	2,704,591	$ 2,987,236	2,704,591
Segment assets, Change in Contribution	$ 282,645
Segment assets, Change in Contribution Percentage	10.00%
Operating Segments | Wealth management
Segment Reporting Information [Line Items]
Net interest income	$ 4,368	3,877	12,837	11,982
Net interest income, Change in Contribution	$ 491		$ 855
Net interest income, Change in Contribution Percentage	13.00%		7.00%
Non-interest income	$ 18,362	18,191	$ 56,103	54,367
Non-interest income, Change in Contribution	$ 171		$ 1,736
Non-interest income, Change in Contribution Percentage	1.00%		3.00%
Net revenue	$ 22,730	22,068	$ 68,940	66,349
Net revenue, Change in Contribution	$ 662		$ 2,591
Net revenue, Change in Contribution Percentage	3.00%		4.00%
Segment profit	$ 3,087	3,067	$ 9,542	9,615
Segment profit, Change in Contribution	$ 20		$ (73)
Segment profit, Change in Contribution Percentage	1.00%		(1.00%)
Segment assets	$ 550,864	519,010	$ 550,864	519,010
Segment assets, Change in Contribution	$ 31,854
Segment assets, Change in Contribution Percentage	6.00%
Intersegment Eliminations
Segment Reporting Information [Line Items]
Net interest income	$ 3,973	3,892	12,258	11,986
Net interest income, Change in Contribution	$ 81		$ 272
Net interest income, Change in Contribution Percentage	2.00%		2.00%
Non-interest income	$ (7,247)	(6,833)	$ (21,605)	(20,370)
Non-interest income, Change in Contribution	$ (414)		$ (1,235)
Non-interest income, Change in Contribution Percentage	(6.00%)		(6.00%)
Net revenue	$ (3,274)	$ (2,941)	$ (9,347)	$ (8,384)
Net revenue, Change in Contribution	$ (333)		$ (963)
Net revenue, Change in Contribution Percentage	(11.00%)		(11.00%)