Segment Reporting - Schedule Of Segment Reporting Information, By Segment (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Net interest income	$ 100,091	$ 100,146
Allowance for loan losses, Provision (benefit)	(580)	28,600
Net interest income after provision for loan losses	100,671	71,546
Noninterest income	55,212	33,369
Noninterest expense	94,049	95,172
Income before income tax expense	61,834	9,743
Income tax provision	14,171	1,298
Net income	47,663	8,445
Total assets	16,726,795	12,343,754	$ 15,964,190
Total liabilities	13,339,750	10,681,020	$ 12,536,138
Other/Eliminations
Segment Reporting Information [Line Items]
Net interest income	0	0
Allowance for loan losses, Provision (benefit)	0	0
Net interest income after provision for loan losses	0	0
Noninterest income	(32)	(22)
Noninterest expense	(1,036)	(935)
Income before income tax expense	1,004	913
Income tax provision	0	0
Net income	1,004	913
Total assets	(63,180)	(60,609)
Total liabilities	(63,180)	(60,609)
Banking Business | Operating Segments
Segment Reporting Information [Line Items]
Net interest income	100,091	100,146
Allowance for loan losses, Provision (benefit)	(580)	28,600
Net interest income after provision for loan losses	100,671	71,546
Noninterest income	26,960	6,868
Noninterest expense	75,274	78,465
Income before income tax expense	52,357	(51)
Income tax provision	11,793	(1,214)
Net income	40,564	1,163
Total assets	16,595,311	12,221,799
Total liabilities	13,359,075	10,696,509
Insurance Agency Business | Operating Segments
Segment Reporting Information [Line Items]
Net interest income	0	0
Allowance for loan losses, Provision (benefit)	0	0
Net interest income after provision for loan losses	0	0
Noninterest income	28,284	26,523
Noninterest expense	19,811	17,642
Income before income tax expense	8,473	8,881
Income tax provision	2,378	2,512
Net income	6,095	6,369
Total assets	194,664	182,564
Total liabilities	$ 43,855	$ 45,120