Borrowed Funds - Schedule of Short-Term Borrowings (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Total short-term borrowings	$ 2,082,880	$ 1,093,280
Short-term borrowings
Debt Instrument [Line Items]
FHLB advances	1,235,000	940,000
Federal funds purchased	678,900	0
Securities sold under agreements to repurchase	168,980	153,280
Total short-term borrowings	$ 2,082,880	$ 1,093,280