Operating Leases - Summary of Right-of-Use Assets Recognized as Component of Premises and Equipment and Lease Liabilities Recognized as Component of Accrued Interest and Other Liabilities in Consolidated Balance Sheet (Detail) $ in Thousands	Sep. 30, 2019 USD ($)
Lessee Disclosure [Abstract]
Right-of-use assets	$ 392,324
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:PropertyPlantAndEquipmentNet
Lease liabilities	$ 424,854
Operating Lease, Liability, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilities