Short-Term Borrowings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Short-term borrowings [Abstract]
Balance at year-end	$ 655,275	$ 871,696
FHLB, unused lines of credit available for short-term financing	2,400,000	1,900,000
Federal Funds Purchased [Member]
Short-term borrowings [Abstract]
Balance at year-end	65,000	80,000	$ 60,000
Average during the year	47,137	66,839	54,162
Maximum month end balance	$ 80,000	$ 80,000	$ 80,000
Weighted average rate during the year	3.90%	3.43%	2.16%
Weighted average rate at year-end	2.84%	4.25%	2.41%
Securities Sold Under Repurchase Agreements [Member]
Short-term borrowings [Abstract]
Balance at year-end	$ 143,775	$ 160,696	$ 182,123
Average during the year	123,337	146,135	175,539
Maximum month end balance	$ 146,410	$ 170,350	$ 190,326
Weighted average rate during the year	0.33%	0.16%	0.07%
Weighted average rate at year-end	0.40%	0.38%	0.07%
Other Short-Term Borrowings [Member]
Short-term borrowings [Abstract]
Balance at year-end	$ 446,500	$ 631,000	$ 477,000
Average during the year	403,453	514,662	460,334
Maximum month end balance	$ 576,000	$ 653,000	$ 591,000
Weighted average rate during the year	1.85%	1.56%	1.02%
Weighted average rate at year-end	1.73%	1.82%	1.18%