Borrowings (Repurchase Agreements) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase, Fair Value of Collateral	$ 689,300
Securities Sold under Agreements to Repurchase	641,487	$ 442,956
Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase	641,500
Available-for-sale Securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase, Fair Value of Collateral		477,600
Government Agency Securities | Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase	432,800
Commercial Mortgage Backed Securities | Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase	$ 208,700
U. S. Treasury | Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase		$ 443,000