Short-Term Borrowings - Components and Selected Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Short-term borrowings
Short-term borrowings	$ 0	$ 400,000
Federal Reserve Bank line of credit
Short-term borrowings
Available remaining borrowing capacity	1,100,000	596,800
Federal funds purchased
Short-term borrowings
Highest month-end balance		110,000	$ 374,875
Average outstanding balance	$ 1,366	$ 16,410	$ 32,987
Weighted-average interest rate paid (as a percent)	0.43%	2.44%	2.18%
FHLB fixed-rate advances
Short-term borrowings
Short-term borrowings	$ 0	$ 400,000
Available remaining borrowing capacity	2,000,000	$ 1,700,000
Weighted-average interest rate (as a percent)		2.84%
Highest month-end balance	400,000	$ 400,000	$ 81,800
Average outstanding balance	$ 208,197	$ 193,425	$ 6,929
Weighted-average interest rate paid (as a percent)	2.88%	2.85%	1.90%