Segment Information (Summary of Segment Information) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net interest income	$ 171,509	$ 151,891
Net interest income, Change in Contribution	$ 19,618
Net interest income, Change in Contribution Percentage	13.00%
Non-interest income	$ 68,752	64,541
Non-interest income, Change in Contribution	$ 4,211
Non-interest income, Change in Contribution Percentage	7.00%
Net revenue	$ 240,261	216,432
Net revenue, Change in Contribution	$ 23,829
Net revenue, Change in Contribution Percentage	11.00%
Segment profit	$ 49,111	39,052
Segment profit, Change in Contribution	$ 10,059
Segment profit, Change in Contribution Percentage	26.00%
Segment assets	$ 23,488,168	20,371,566	$ 22,909,348
Segment assets, Change in Contribution	$ 3,116,602
Segment assets, Change in Contribution Percentage	15.00%
Operating Segments
Segment Reporting Information [Line Items]
Net interest income	$ 167,361	147,916
Net interest income, Change in Contribution	$ 19,445
Net interest income, Change in Contribution Percentage	13.00%
Non-interest income	$ 76,822	71,511
Non-interest income, Change in Contribution	$ 5,311
Non-interest income, Change in Contribution Percentage	7.00%
Net revenue	$ 244,183	219,427
Net revenue, Change in Contribution	$ 24,756
Net revenue, Change in Contribution Percentage	11.00%
Operating Segments | Community banking
Segment Reporting Information [Line Items]
Net interest income	$ 141,698	122,681
Net interest income, Change in Contribution	$ 19,017
Net interest income, Change in Contribution Percentage	16.00%
Non-interest income	$ 45,667	44,912
Non-interest income, Change in Contribution	$ 755
Non-interest income, Change in Contribution Percentage	2.00%
Net revenue	$ 187,365	167,593
Net revenue, Change in Contribution	$ 19,772
Net revenue, Change in Contribution Percentage	12.00%
Segment profit	$ 34,757	24,965
Segment profit, Change in Contribution	$ 9,792
Segment profit, Change in Contribution Percentage	39.00%
Segment assets	$ 19,575,709	17,039,668
Segment assets, Change in Contribution	$ 2,536,041
Segment assets, Change in Contribution Percentage	15.00%
Operating Segments | Specialty finance
Segment Reporting Information [Line Items]
Net interest income	$ 21,180	21,046
Net interest income, Change in Contribution	$ 134
Net interest income, Change in Contribution Percentage	1.00%
Non-interest income	$ 12,403	7,871
Non-interest income, Change in Contribution	$ 4,532
Non-interest income, Change in Contribution Percentage	58.00%
Net revenue	$ 33,583	28,917
Net revenue, Change in Contribution	$ 4,666
Net revenue, Change in Contribution Percentage	16.00%
Segment profit	$ 11,472	10,952
Segment profit, Change in Contribution	$ 520
Segment profit, Change in Contribution Percentage	5.00%
Segment assets	$ 3,322,807	2,783,958
Segment assets, Change in Contribution	$ 538,849
Segment assets, Change in Contribution Percentage	19.00%
Operating Segments | Wealth management
Segment Reporting Information [Line Items]
Net interest income	$ 4,483	4,189
Net interest income, Change in Contribution	$ 294
Net interest income, Change in Contribution Percentage	7.00%
Non-interest income	$ 18,752	18,728
Non-interest income, Change in Contribution	$ 24
Non-interest income, Change in Contribution Percentage	0.00%
Net revenue	$ 23,235	22,917
Net revenue, Change in Contribution	$ 318
Net revenue, Change in Contribution Percentage	1.00%
Segment profit	$ 2,882	3,135
Segment profit, Change in Contribution	$ (253)
Segment profit, Change in Contribution Percentage	(8.00%)
Segment assets	$ 589,652	547,940
Segment assets, Change in Contribution	$ 41,712
Segment assets, Change in Contribution Percentage	8.00%
Intersegment Eliminations
Segment Reporting Information [Line Items]
Net interest income	$ 4,148	3,975
Net interest income, Change in Contribution	$ 173
Net interest income, Change in Contribution Percentage	4.00%
Non-interest income	$ (8,070)	(6,970)
Non-interest income, Change in Contribution	$ (1,100)
Non-interest income, Change in Contribution Percentage	(16.00%)
Net revenue	$ (3,922)	$ (2,995)
Net revenue, Change in Contribution	$ (927)
Net revenue, Change in Contribution Percentage	(31.00%)