Schedule of Segment Financial Results (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Net interest income	$ 124,765	$ 109,895	$ 363,867	$ 297,613
Provision for loan losses	13,000	2,500	25,000	10,500
Noninterest income	121,948	109,098	359,745	353,855
Noninterest expense	179,783	185,279	545,570	521,656
Income before income taxes	53,930	31,214	153,042	119,312
Income tax expense	11,984	8,763	37,175	32,882
Net Income	41,946	22,451	115,867	86,430
Average assets	19,692,000	18,120,000	19,488,000	17,460,000
Bank [Member]
Segment Reporting Information [Line Items]
Net interest income	121,963	108,424	355,847	294,210
Provision for loan losses	13,000	2,500	25,000	10,500
Noninterest income	80,454	65,207	235,915	210,695
Noninterest expense	142,836	149,269	431,594	407,997
Income before income taxes	46,581	21,862	135,168	86,408
Income tax expense	10,427	6,120	32,928	23,859
Net Income	36,154	15,742	102,240	62,549
Average assets	18,384,000	17,045,000	18,147,000	16,419,000
Institutional Investment Management [Member]
Segment Reporting Information [Line Items]
Net interest income		49		27
Noninterest income	19,413	21,398	56,965	74,182
Noninterest expense	16,874	16,495	52,993	52,799
Income before income taxes	2,539	4,952	3,972	21,410
Income tax expense	519	1,409	899	5,899
Net Income	2,020	3,543	3,073	15,511
Average assets	61,000	66,000	62,000	71,000
Asset Servicing [Member]
Segment Reporting Information [Line Items]
Net interest income	2,802	1,422	8,020	3,376
Noninterest income	22,081	22,493	66,865	68,978
Noninterest expense	20,073	19,515	60,983	60,860
Income before income taxes	4,810	4,400	13,902	11,494
Income tax expense	1,038	1,234	3,348	3,124
Net Income	3,772	3,166	10,554	8,370
Average assets	$ 1,247,000	$ 1,009,000	$ 1,279,000	$ 970,000