Schedule of Segment Financial Results (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Net interest income	$ 121,210	$ 97,360	$ 239,102	$ 187,718
Provision for loan losses	7,000	5,000	12,000	8,000
Noninterest income	121,447	119,550	237,797	244,757
Noninterest expense	185,243	171,964	365,987	336,377
Income before income taxes	50,414	39,946	98,912	88,098
Income tax expense	13,117	9,732	25,370	24,119
Net Income	37,297	30,214	73,542	63,979
Average assets	19,436,000	17,413,000	19,385,000	17,124,000
Bank [Member]
Segment Reporting Information [Line Items]
Net interest income	118,613	96,403	233,885	185,764
Provision for loan losses	7,000	5,000	12,000	8,000
Noninterest income	80,044	70,840	155,483	145,529
Noninterest expense	145,736	133,617	289,104	258,796
Income before income taxes	45,921	28,626	88,264	64,497
Income tax expense	11,939	7,017	22,643	17,732
Net Income	33,982	21,609	65,621	46,765
Average assets	18,170,000	16,384,000	18,027,000	16,101,000
Institutional Investment Management [Member]
Segment Reporting Information [Line Items]
Noninterest income	19,127	25,685	37,542	52,769
Noninterest expense	18,858	18,302	36,088	36,262
Income before income taxes	269	7,383	1,454	16,507
Income tax expense	77	1,747	367	4,497
Net Income	192	5,636	1,087	12,010
Average assets	61,000	71,000	62,000	73,000
Asset Servicing [Member]
Segment Reporting Information [Line Items]
Net interest income	2,597	957	5,217	1,954
Noninterest income	22,276	23,025	44,772	46,459
Noninterest expense	20,649	20,045	40,795	41,319
Income before income taxes	4,224	3,937	9,194	7,094
Income tax expense	1,101	968	2,360	1,890
Net Income	3,123	2,969	6,834	5,204
Average assets	$ 1,205,000	$ 958,000	$ 1,296,000	$ 950,000