Credit Quality - Schedule of Age Analysis of its Past Due Loans, Segregated by Class of Loans (Parenthetical) (Detail) $ in Thousands	Dec. 31, 2019 USD ($)
Financing Receivable, Recorded Investment, Past Due [Line Items]
Acquired impaired loans from merger	$ 13,713,548
Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Acquired impaired loans from merger	96,004
Loans Acquired with Deteriorated Credit Quality [Member] | Loans and Debt Securities Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Acquired impaired loans from merger	$ 96,004