Cash Due from Banks Interest-Bearing Deposits and Federal Funds Sold - Summary of Average Amount of Required Reserves (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Average Amount Of Required Reserves [Abstract]
Vault cash and funds on deposit with the Federal Reserve Bank	$ 1,299,872	$ 1,639,058
Average required Reserves	$ 45,195	$ 44,485

Amount of pass-through reserves deposited with Federal Reserve Banks from member institutions of Federal Home Loan Banks (FHLBanks).

No definition available.

Name:	us-gaap_CashPassThroughReserveFederalHomeLoanBank
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant