Loans - Non-Accrual Loans, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	$ 79,461	$ 102,303
Non-accrual with no credit loss allowance	50,740	24,692
Commercial Portfolio Segment [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	27,146	26,038
Non-accrual with no credit loss allowance	10,623	13,266
Commercial and Industrial Total Energy Loans [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	36,239	65,761
Non-accrual with no credit loss allowance	30,892	3,281
Paycheck Protection Program [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	0	0
Non-accrual with no credit loss allowance	0	0
Commercial Real Estate Buildings Land And Other Loans [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	12,154	8,912
Non-accrual with no credit loss allowance	6,513	6,558
Construction Loans [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	1,869	665
Non-accrual with no credit loss allowance	677	665
Total consumer real estate loans [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	2,035	922
Non-accrual with no credit loss allowance	2,035	922
Consumer Loan [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	18	5
Non-accrual with no credit loss allowance	$ 0	$ 0