Segment Reporting - Schedule Of Segment Reporting Information, By Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Segment Reporting Information [Line Items]
Net interest income	$ 152,179	$ 102,691	$ 418,060	$ 307,390
Provision for (release of) allowance for loan losses	6,480	(1,488)	7,045	(5,368)
Net interest income after provision for loan losses	145,699	104,179	411,015	312,758
Noninterest income	43,353	43,209	131,645	144,154
Noninterest expense	116,840	98,970	336,845	300,354
Income before income tax expense	72,212	48,418	205,815	156,558
Income tax expense	17,435	11,312	48,350	36,980
Net income	54,777	37,106	157,465	119,578
Total assets	22,042,933	17,461,223	22,042,933	17,461,223	$ 23,512,128
Total liabilities	19,626,770	14,031,931	19,626,770	14,031,931	$ 20,105,776
Eliminations And Reconciling Items
Segment Reporting Information [Line Items]
Net interest income	0	0	0	0
Provision for (release of) allowance for loan losses	0	0	0	0
Net interest income after provision for loan losses	0	0	0	0
Noninterest income	(138)	(82)	(328)	(113)
Noninterest expense	(1,106)	(1,042)	(3,164)	(3,039)
Income before income tax expense	968	960	2,836	2,926
Income tax expense	0	0	0	0
Net income	968	960	2,836	2,926
Total assets	(73,558)	(71,589)	(73,558)	(71,589)
Total liabilities	(73,558)	(71,589)	(73,558)	(71,589)
Business Banking | Operating Segments
Segment Reporting Information [Line Items]
Net interest income	152,179	102,691	418,060	307,390
Provision for (release of) allowance for loan losses	6,480	(1,488)	7,045	(5,368)
Net interest income after provision for loan losses	145,699	104,179	411,015	312,758
Noninterest income	19,777	20,783	55,919	69,308
Noninterest expense	96,749	80,474	279,823	243,549
Income before income tax expense	68,727	44,488	187,111	138,517
Income tax expense	16,717	10,471	43,870	32,728
Net income	52,010	34,017	143,241	105,789
Total assets	21,894,550	17,324,816	21,894,550	17,324,816
Total liabilities	19,644,824	14,051,100	19,644,824	14,051,100
Insurance Agency Business | Operating Segments
Segment Reporting Information [Line Items]
Net interest income	0	0	0	0
Provision for (release of) allowance for loan losses	0	0	0	0
Net interest income after provision for loan losses	0	0	0	0
Noninterest income	23,714	22,508	76,054	74,959
Noninterest expense	21,197	19,538	60,186	59,844
Income before income tax expense	2,517	2,970	15,868	15,115
Income tax expense	718	841	4,480	4,252
Net income	1,799	2,129	11,388	10,863
Total assets	221,941	207,996	221,941	207,996
Total liabilities	$ 55,504	$ 52,420	$ 55,504	$ 52,420