Segment Information (Summary of Segment Information) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net interest income	$ 204,409	$ 175,270	$ 396,989	$ 346,779
Net interest income, Change in Contribution	$ 29,139		$ 50,210
Net interest income, Change in Contribution Percentage	17.00%		14.00%
Non-interest income	$ 89,972	84,799	$ 158,737	153,551
Non-interest income, Change in Contribution	$ 5,173		$ 5,186
Non-interest income, Change in Contribution Percentage	6.00%		3.00%
Net revenue	$ 294,381	260,069	$ 555,726	500,330
Net revenue, Change in Contribution	$ 34,312		$ 55,396
Net revenue, Change in Contribution Percentage	13.00%		11.00%
Segment profit	$ 64,897	50,041	$ 123,275	99,152
Segment profit, Change in Contribution	$ 14,856		$ 24,123
Segment profit, Change in Contribution Percentage	30.00%		24.00%
Segment assets	$ 26,929,265	24,420,616	$ 26,929,265	24,420,616	$ 25,668,553
Segment assets, Change in Contribution	$ 2,508,649
Segment assets, Change in Contribution Percentage	10.00%
Operating Segments
Segment Reporting Information [Line Items]
Net interest income	$ 199,806	170,986	387,954	338,347
Net interest income, Change in Contribution	$ 28,820		$ 49,607
Net interest income, Change in Contribution Percentage	17.00%		15.00%
Non-interest income	$ 99,301	93,158	$ 176,975	169,980
Non-interest income, Change in Contribution	$ 6,143		$ 6,995
Non-interest income, Change in Contribution Percentage	7.00%		4.00%
Net revenue	$ 299,107	264,144	$ 564,929	508,327
Net revenue, Change in Contribution	$ 34,963		$ 56,602
Net revenue, Change in Contribution Percentage	13.00%		11.00%
Operating Segments | Community banking
Segment Reporting Information [Line Items]
Net interest income	$ 166,329	142,251	$ 322,609	283,949
Net interest income, Change in Contribution	$ 24,078		$ 38,660
Net interest income, Change in Contribution Percentage	17.00%		14.00%
Non-interest income	$ 65,007	60,813	$ 107,723	106,480
Non-interest income, Change in Contribution	$ 4,194		$ 1,243
Non-interest income, Change in Contribution Percentage	7.00%		1.00%
Net revenue	$ 231,336	203,064	$ 430,332	390,429
Net revenue, Change in Contribution	$ 28,272		$ 39,903
Net revenue, Change in Contribution Percentage	14.00%		10.00%
Segment profit	$ 46,026	34,576	$ 83,703	69,333
Segment profit, Change in Contribution	$ 11,450		$ 14,370
Segment profit, Change in Contribution Percentage	33.00%		21.00%
Segment assets	$ 22,032,302	20,190,707	$ 22,032,302	20,190,707
Segment assets, Change in Contribution	$ 1,841,595
Segment assets, Change in Contribution Percentage	9.00%
Operating Segments | Specialty finance
Segment Reporting Information [Line Items]
Net interest income	$ 28,558	24,352	55,370	45,532
Net interest income, Change in Contribution	$ 4,206		$ 9,838
Net interest income, Change in Contribution Percentage	17.00%		22.00%
Non-interest income	$ 13,721	12,482	$ 27,877	24,885
Non-interest income, Change in Contribution	$ 1,239		$ 2,992
Non-interest income, Change in Contribution Percentage	10.00%		12.00%
Net revenue	$ 42,279	36,834	$ 83,247	70,417
Net revenue, Change in Contribution	$ 5,445		$ 12,830
Net revenue, Change in Contribution Percentage	15.00%		18.00%
Segment profit	$ 14,849	12,044	$ 30,947	23,516
Segment profit, Change in Contribution	$ 2,805		$ 7,431
Segment profit, Change in Contribution Percentage	23.00%		32.00%
Segment assets	$ 4,255,109	3,645,077	$ 4,255,109	3,645,077
Segment assets, Change in Contribution	$ 610,032
Segment assets, Change in Contribution Percentage	17.00%
Operating Segments | Wealth management
Segment Reporting Information [Line Items]
Net interest income	$ 4,919	4,383	9,975	8,866
Net interest income, Change in Contribution	$ 536		$ 1,109
Net interest income, Change in Contribution Percentage	12.00%		13.00%
Non-interest income	$ 20,573	19,863	$ 41,375	38,615
Non-interest income, Change in Contribution	$ 710		$ 2,760
Non-interest income, Change in Contribution Percentage	4.00%		7.00%
Net revenue	$ 25,492	24,246	$ 51,350	47,481
Net revenue, Change in Contribution	$ 1,246		$ 3,869
Net revenue, Change in Contribution Percentage	5.00%		8.00%
Segment profit	$ 4,022	3,421	$ 8,625	6,303
Segment profit, Change in Contribution	$ 601		$ 2,322
Segment profit, Change in Contribution Percentage	18.00%		37.00%
Segment assets	$ 641,854	584,832	$ 641,854	584,832
Segment assets, Change in Contribution	$ 57,022
Segment assets, Change in Contribution Percentage	10.00%
Intersegment Eliminations
Segment Reporting Information [Line Items]
Net interest income	$ 4,603	4,284	9,035	8,432
Net interest income, Change in Contribution	$ 319		$ 603
Net interest income, Change in Contribution Percentage	7.00%		7.00%
Non-interest income	$ (9,329)	(8,359)	$ (18,238)	(16,429)
Non-interest income, Change in Contribution	$ (970)		$ (1,809)
Non-interest income, Change in Contribution Percentage	(12.00%)		(11.00%)
Net revenue	$ (4,726)	$ (4,075)	$ (9,203)	$ (7,997)
Net revenue, Change in Contribution	$ (651)		$ (1,206)
Net revenue, Change in Contribution Percentage	(16.00%)		(15.00%)