Segment Reporting - Schedule Of Segment Reporting Information, By Segment (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Segment Reporting Information [Line Items]
Net interest income	$ 138,309	$ 128,124
Provision for (release of) allowance for loan losses	25	(485)
Net interest income after provision for (release of) allowance for loan losses	138,284	128,609
Noninterest (loss) income	(278,330)	46,415
Noninterest expense	116,294	108,866
(Loss) income before income tax (benefit) expense	(256,340)	66,158
Income tax (benefit) expense	(62,244)	14,642
Net (loss) income	(194,096)	51,516
Total assets	22,720,530	22,836,072	$ 22,646,858
Total liabilities	20,141,407	19,827,680	$ 20,175,068
Eliminations And Reconciling Items
Segment Reporting Information [Line Items]
Net interest income	0	0
Provision for (release of) allowance for loan losses	0	0
Net interest income after provision for (release of) allowance for loan losses	0	0
Noninterest (loss) income	(168)	(171)
Noninterest expense	(1,240)	(1,053)
(Loss) income before income tax (benefit) expense	1,072	882
Income tax (benefit) expense	0	0
Net (loss) income	1,072	882
Total assets	(77,474)	(71,224)
Total liabilities	(77,474)	(71,224)
Business Banking | Operating Segments
Segment Reporting Information [Line Items]
Net interest income	138,309	128,124
Provision for (release of) allowance for loan losses	25	(485)
Net interest income after provision for (release of) allowance for loan losses	138,284	128,609
Noninterest (loss) income	(310,206)	18,137
Noninterest expense	95,946	90,446
(Loss) income before income tax (benefit) expense	(267,868)	56,300
Income tax (benefit) expense	(65,193)	12,108
Net (loss) income	(202,675)	44,192
Total assets	22,579,422	22,695,895
Total liabilities	20,174,053	19,848,995
Insurance Agency Business | Operating Segments
Segment Reporting Information [Line Items]
Net interest income	0	0
Provision for (release of) allowance for loan losses	0	0
Net interest income after provision for (release of) allowance for loan losses	0	0
Noninterest (loss) income	32,044	28,449
Noninterest expense	21,588	19,473
(Loss) income before income tax (benefit) expense	10,456	8,976
Income tax (benefit) expense	2,949	2,534
Net (loss) income	7,507	6,442
Total assets	218,582	211,401
Total liabilities	$ 44,828	$ 49,909