Segment Reporting - Schedule Of Segment Reporting Information, By Segment (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Segment Reporting Information [Line Items]
Net interest income	$ 128,124	$ 100,091
(Release of) provision for loan losses	(485)	(580)
Net interest income after provision for loan losses	128,609	100,671
Noninterest income	46,415	55,212
Noninterest expense	108,866	94,049
Income before provision for income taxes	66,158	61,834
Income tax provision	14,642	14,171
Net income	51,516	47,663
Total assets	22,836,072	16,726,795	$ 23,512,128
Total liabilities	19,827,680	13,339,750	$ 20,105,776
Eliminations And Reconciling Items
Segment Reporting Information [Line Items]
Net interest income	0	0
(Release of) provision for loan losses	0	0
Net interest income after provision for loan losses	0	0
Noninterest income	(171)	(32)
Noninterest expense	(1,053)	(1,036)
Income before provision for income taxes	882	1,004
Income tax provision	0	0
Net income	882	1,004
Total assets	(71,224)	(63,180)
Total liabilities	(71,224)	(63,180)
Business Banking | Operating Segments
Segment Reporting Information [Line Items]
Net interest income	128,124	100,091
(Release of) provision for loan losses	(485)	(580)
Net interest income after provision for loan losses	128,609	100,671
Noninterest income	18,137	26,960
Noninterest expense	90,446	75,274
Income before provision for income taxes	56,300	52,357
Income tax provision	12,108	11,793
Net income	44,192	40,564
Total assets	22,695,895	16,595,311
Total liabilities	19,848,995	13,359,075
Insurance Agency Business | Operating Segments
Segment Reporting Information [Line Items]
Net interest income	0	0
(Release of) provision for loan losses	0	0
Net interest income after provision for loan losses	0	0
Noninterest income	28,449	28,284
Noninterest expense	19,473	19,811
Income before provision for income taxes	8,976	8,473
Income tax provision	2,534	2,378
Net income	6,442	6,095
Total assets	211,401	194,664
Total liabilities	$ 49,909	$ 43,855