Business Combinations - Summary of Contractually Required Principal and Interest Cash Payments for Purchased Credit Impaired Loans (Detail) - National Commerce Corporation [Member] - Purchased Credit-Impaired [Member] $ in Thousands	Apr. 01, 2019 USD ($)
Business Acquisition [Line Items]
Contractually required principal and interest	$ 51,527
Non-accretable difference	(29,187)
Cash flows expected to be collected	22,340
Accretable yield	(3,724)
Total purchased credit-impaired loans acquired	$ 18,616