Borrowed Funds - Schedule of Short-Term Borrowings (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Total short-term borrowings	$ 1,093,280	$ 2,118,914
Short-term borrowings
Debt Instrument [Line Items]
FHLB advances	940,000	1,732,000
Securities sold under agreements to repurchase	153,280	261,914
Federal funds purchased	0	125,000
Total short-term borrowings	$ 1,093,280	$ 2,118,914