Loans - Activity in the Allowance for Credit Losses on Loans by Portfolio Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance			$ 227,621
Ending balance	$ 242,235		242,235
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	75,166	$ 87,270	104,237	$ 72,091
Credit loss, expense (reversal)	(623)	10,844	(18,903)	29,347
Charge-offs	(943)	(572)	(14,259)	(5,918)
Recoveries	707	1,288	3,232	3,310
Net charge-offs	(236)	716	(11,027)	(2,608)
Ending balance	74,307	98,830	74,307	98,830
Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	14,929	16,267	18,062	17,217
Credit loss, expense (reversal)	1,784	2,491	(1,683)	874
Charge-offs	0	0	(518)	(371)
Recoveries	353	93	1,205	1,131
Net charge-offs	353	93	687	760
Ending balance	17,066	18,851	17,066	18,851
Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	120,926	117,106	90,301	144,936
Credit loss, expense (reversal)	5,424	(16,522)	35,918	(44,363)
Charge-offs	(62)	0	(62)	(702)
Recoveries	204	23	335	736
Net charge-offs	142	23	273	34
Ending balance	126,492	100,607	126,492	100,607
Total consumer real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	13,035	6,854	8,004	6,585
Credit loss, expense (reversal)	2,130	940	7,235	1,497
Charge-offs	(170)	(68)	(1,500)	(430)
Recoveries	44	309	1,300	383
Net charge-offs	(126)	241	(200)	(47)
Ending balance	15,039	8,035	15,039	8,035
Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	9,563	12,135	7,017	7,837
Credit loss, expense (reversal)	4,893	(216)	15,649	10,250
Charge-offs	(8,189)	(6,549)	(22,147)	(17,642)
Recoveries	3,064	2,622	8,812	7,547
Net charge-offs	(5,125)	(3,927)	(13,335)	(10,095)
Ending balance	9,331	7,992	9,331	7,992
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	233,619	239,632	227,621	248,666
Credit loss, expense (reversal)	13,608	(2,463)	38,216	(2,395)
Charge-offs	(9,364)	(7,189)	(38,486)	(25,063)
Recoveries	4,372	4,335	14,884	13,107
Net charge-offs	(4,992)	(2,854)	(23,602)	(11,956)
Ending balance	$ 242,235	$ 234,315	$ 242,235	$ 234,315