Loans - Activity in the Allowance for Credit Losses on Loans by Portfolio Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance			$ 248,666
Ending balance	$ 239,632		239,632
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	87,026	$ 70,892	72,091	$ 73,843
Credit loss, expense (reversal)	942	(5,901)	18,503	(7,866)
Charge-offs	(1,891)	(685)	(5,346)	(2,874)
Recoveries	1,193	965	2,022	2,168
Net charge-offs	(698)	280	(3,324)	(706)
Ending balance	87,270	65,271	87,270	65,271
Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	15,422	33,472	17,217	39,553
Credit loss, expense (reversal)	427	(5,527)	(1,617)	(11,328)
Charge-offs	0	0	(371)	(1,433)
Recoveries	418	65	1,038	1,218
Net charge-offs	418	65	667	(215)
Ending balance	16,267	28,010	16,267	28,010
Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	128,954	144,440	144,936	134,892
Credit loss, expense (reversal)	(12,232)	3,654	(27,841)	12,576
Charge-offs	0	(137)	(702)	(137)
Recoveries	384	36	713	662
Net charge-offs	384	(101)	11	525
Ending balance	117,106	147,993	117,106	147,993
Total consumer real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	6,359	5,636	6,585	7,926
Credit loss, expense (reversal)	583	611	557	(2,111)
Charge-offs	(131)	(388)	(362)	(672)
Recoveries	43	295	74	1,011
Net charge-offs	(88)	(93)	(288)	339
Ending balance	6,854	6,154	6,854	6,154
Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	9,074	6,818	7,837	6,963
Credit loss, expense (reversal)	5,884	2,784	10,466	4,350
Charge-offs	(5,322)	(3,882)	(11,093)	(7,942)
Recoveries	2,499	2,140	4,925	4,489
Net charge-offs	(2,823)	(1,742)	(6,168)	(3,453)
Ending balance	12,135	7,860	12,135	7,860
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	246,835	261,258	248,666	263,177
Credit loss, expense (reversal)	(4,396)	(4,379)	68	(4,379)
Charge-offs	(7,344)	(5,092)	(17,874)	(13,058)
Recoveries	4,537	3,501	8,772	9,548
Net charge-offs	(2,807)	(1,591)	(9,102)	(3,510)
Ending balance	$ 239,632	$ 255,288	$ 239,632	$ 255,288