Short-Term Borrowings - Components and Selected Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Short-term borrowings
Short-term borrowings	$ 400,000
Short-term FHLB fixed-rate advance:
Short-term borrowings
Available remaining borrowing capacity	1,700,000	$ 1,300,000
Federal Reserve Bank line of credit
Short-term borrowings
Available remaining borrowing capacity	596,800	671,800
Federal funds purchased
Short-term borrowings
Highest month-end balance	110,000	374,875	$ 6,000
Average outstanding balance	$ 16,410	$ 32,987	$ 1,280
Weighted-average interest rate paid (as a percent)	2.44%	2.18%	0.97%
Securities sold under agreements to repurchase
Short-term borrowings
Highest month-end balance			$ 5,951
Average outstanding balance			$ 893
Weighted-average interest rate paid (as a percent)			0.55%
Short-term FHLB fixed-rate advance:
Short-term borrowings
Short-term borrowings	$ 400,000
Weighted-average interest rate (as a percent)	2.84%
Highest month-end balance	$ 400,000	$ 81,800
Average outstanding balance	$ 193,425	$ 6,929
Weighted-average interest rate paid (as a percent)	2.85%	1.90%