Borrowings, Short-Term Borrowings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Short-term borrowings [Abstract]
Balance at year-end	$ 168,386	$ 655,275
FHLB, unused lines of credit available for short-term financing	3,100,000	2,400,000
Federal Funds Purchased [Member]
Short-term borrowings [Abstract]
Balance at year-end	0	65,000	$ 80,000
Average during the year	14,727	47,137	66,839
Maximum month end balance	$ 40,000	$ 80,000	$ 80,000
Weighted average rate during the year	2.05%	3.90%	3.43%
Weighted average rate at year-end	0.00%	2.84%	4.25%
Securities Sold Under Repurchase Agreements [Member]
Short-term borrowings [Abstract]
Balance at year-end	$ 143,386	$ 143,775	$ 160,696
Average during the year	154,383	123,337	146,135
Maximum month end balance	$ 176,840	$ 146,410	$ 170,350
Weighted average rate during the year	0.17%	0.33%	0.16%
Weighted average rate at year-end	0.20%	0.40%	0.38%
Other Short-Term Borrowings [Member]
Short-term borrowings [Abstract]
Balance at year-end	$ 25,000	$ 446,500	$ 631,000
Average during the year	183,699	403,453	514,662
Maximum month end balance	$ 366,500	$ 576,000	$ 653,000
Weighted average rate during the year	1.55%	1.85%	1.56%
Weighted average rate at year-end	1.99%	1.73%	1.82%