Segment Reporting - Schedule Of Segment Reporting Information, By Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Segment Reporting Information [Line Items]
Net interest income	$ 141,588	$ 137,757	$ 279,897	$ 265,881
Provision for allowance for loan losses	7,501	1,050	7,526	565
Net interest income after provision for allowance for loan losses	134,087	136,707	272,371	265,316
Noninterest (loss) income	53,831	41,877	(224,499)	88,292
Noninterest expense	121,648	111,139	237,942	220,005
Income (loss) before income tax expense (benefit)	66,270	67,445	(190,070)	133,603
Income tax expense (benefit)	17,613	16,273	(44,631)	30,915
Net income (loss)	48,657	51,172	(145,439)	102,688
Total assets	21,583,493	22,350,848	21,583,493	22,350,848	$ 22,646,858
Total liabilities	19,056,721	19,632,452	19,056,721	19,632,452	$ 20,175,068
Eliminations And Reconciling Items
Segment Reporting Information [Line Items]
Net interest income	0	0	0	0
Provision for allowance for loan losses	0	0	0	0
Net interest income after provision for allowance for loan losses	0	0	0	0
Noninterest (loss) income	0	(19)	(168)	(190)
Noninterest expense	(955)	(1,005)	(2,195)	(2,058)
Income (loss) before income tax expense (benefit)	955	986	2,027	1,868
Income tax expense (benefit)	0	0	0	0
Net income (loss)	955	986	2,027	1,868
Total assets	(87,434)	(77,255)	(87,434)	(77,255)
Total liabilities	(87,434)	(77,255)	(87,434)	(77,255)
Business Banking | Operating Segments
Segment Reporting Information [Line Items]
Net interest income	141,588	137,757	279,897	265,881
Provision for allowance for loan losses	7,501	1,050	7,526	565
Net interest income after provision for allowance for loan losses	134,087	136,707	272,371	265,316
Noninterest (loss) income	25,948	18,005	(284,258)	36,142
Noninterest expense	100,806	92,628	196,752	183,074
Income (loss) before income tax expense (benefit)	59,229	62,084	(208,639)	118,384
Income tax expense (benefit)	15,891	15,045	(49,302)	27,153
Net income (loss)	43,338	47,039	(159,337)	91,231
Total assets	21,442,008	22,210,434	21,442,008	22,210,434
Total liabilities	19,093,354	19,656,675	19,093,354	19,656,675
Insurance Agency Business | Operating Segments
Segment Reporting Information [Line Items]
Net interest income	0	0	0	0
Provision for allowance for loan losses	0	0	0	0
Net interest income after provision for allowance for loan losses	0	0	0	0
Noninterest (loss) income	27,883	23,891	59,927	52,340
Noninterest expense	21,797	19,516	43,385	38,989
Income (loss) before income tax expense (benefit)	6,086	4,375	16,542	13,351
Income tax expense (benefit)	1,722	1,228	4,671	3,762
Net income (loss)	4,364	3,147	11,871	9,589
Total assets	228,919	217,669	228,919	217,669
Total liabilities	$ 50,801	$ 53,032	$ 50,801	$ 53,032