Segment Information (Summary of Segment Information) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Total net interest income	$ 151,891	$ 144,006
Total net interest income, Change in Contribution	7,885
Total net interest income, Change in Contribution Percentage	5.00%
Total non-interest income	64,541	45,529
Total non-interest income, Change in Contribution	19,012
Total non-interest income, Change in Contribution Percentage	42.00%
Total net revenue	216,432	189,535
Total net revenue, Change in Contribution	26,897
Total net revenue, Change in Contribution Percentage	14.00%
Net income	39,052	34,500
Total segment profit, Change in Contribution	4,552
Total segment profit, Change in Contribution Percentage	13.00%
Total assets	20,382,271	18,221,163	20,010,727
Total segment assets, Change in Contribution	2,161,108
Total segment assets, Change in Contribution Percentage	12.00%
Operating Segments
Segment Reporting Information [Line Items]
Total net interest income	147,916	140,066
Total net interest income, Change in Contribution	7,850
Total net interest income, Change in Contribution Percentage	6.00%
Total non-interest income	71,511	52,141
Total non-interest income, Change in Contribution	19,370
Total non-interest income, Change in Contribution Percentage	37.00%
Total net revenue	219,427	192,207
Total net revenue, Change in Contribution	27,220
Total net revenue, Change in Contribution Percentage	14.00%
Operating Segments | Community banking
Segment Reporting Information [Line Items]
Total net interest income	122,681	116,755
Total net interest income, Change in Contribution	5,926
Total net interest income, Change in Contribution Percentage	5.00%
Total non-interest income	44,912	27,319
Total non-interest income, Change in Contribution	17,593
Total non-interest income, Change in Contribution Percentage	64.00%
Total net revenue	167,593	144,074
Total net revenue, Change in Contribution	23,519
Total net revenue, Change in Contribution Percentage	16.00%
Net income	24,965	22,581
Total segment profit, Change in Contribution	2,384
Total segment profit, Change in Contribution Percentage	11.00%
Total assets	17,050,262	15,160,507
Total segment assets, Change in Contribution	1,889,755
Total segment assets, Change in Contribution Percentage	12.00%
Operating Segments | Specialty finance
Segment Reporting Information [Line Items]
Total net interest income	21,046	19,212
Total net interest income, Change in Contribution	1,834
Total net interest income, Change in Contribution Percentage	10.00%
Total non-interest income	7,871	7,881
Total non-interest income, Change in Contribution	(10)
Total non-interest income, Change in Contribution Percentage	0.00%
Total net revenue	28,917	27,093
Total net revenue, Change in Contribution	1,824
Total net revenue, Change in Contribution Percentage	7.00%
Net income	10,952	8,982
Total segment profit, Change in Contribution	1,970
Total segment profit, Change in Contribution Percentage	22.00%
Total assets	2,784,069	2,532,362
Total segment assets, Change in Contribution	251,707
Total segment assets, Change in Contribution Percentage	10.00%
Operating Segments | Wealth management
Segment Reporting Information [Line Items]
Total net interest income	4,189	4,099
Total net interest income, Change in Contribution	90
Total net interest income, Change in Contribution Percentage	2.00%
Total non-interest income	18,728	16,941
Total non-interest income, Change in Contribution	1,787
Total non-interest income, Change in Contribution Percentage	11.00%
Total net revenue	22,917	21,040
Total net revenue, Change in Contribution	1,877
Total net revenue, Change in Contribution Percentage	9.00%
Net income	3,135	2,937
Total segment profit, Change in Contribution	198
Total segment profit, Change in Contribution Percentage	7.00%
Total assets	547,940	528,294
Total segment assets, Change in Contribution	19,646
Total segment assets, Change in Contribution Percentage	4.00%
Intersegment Eliminations
Segment Reporting Information [Line Items]
Total net interest income	3,975	3,940
Total net interest income, Change in Contribution	35
Total net interest income, Change in Contribution Percentage	1.00%
Total non-interest income	(6,970)	(6,612)
Total non-interest income, Change in Contribution	(358)
Total non-interest income, Change in Contribution Percentage	(5.00%)
Total net revenue	(2,995)	(2,672)
Total net revenue, Change in Contribution	$ (323)
Total net revenue, Change in Contribution Percentage	(12.00%)