Loans - Non-Accrual Loans, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	$ 66,727	$ 102,303
Non-accrual with no credit loss allowance	48,487	24,692
Commercial Portfolio Segment [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	23,913	26,038
Non-accrual with no credit loss allowance	11,085	13,266
Commercial and Industrial Total Energy Loans [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	28,702	65,761
Non-accrual with no credit loss allowance	28,702	3,281
Commercial Real Estate Buildings Land And Other Loans [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	8,224	8,912
Non-accrual with no credit loss allowance	5,922	6,558
Construction Loans [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	3,774	665
Non-accrual with no credit loss allowance	683	665
Total consumer real estate loans [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	2,094	922
Non-accrual with no credit loss allowance	2,094	922
Consumer Loan [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	20	5
Non-accrual with no credit loss allowance	$ 1	$ 0