Borrowings (Repurchase Agreements) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase, Fair Value of Collateral	$ 477,600
Securities Sold under Agreements to Repurchase	442,956	$ 543,936
Available-for-sale Securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase, Fair Value of Collateral		598,600
Government Agency Securities \| Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase	$ 443,000
U. S. Treasury \| Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase		$ 543,900

Amount, after the effects of master netting arrangements, of funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Name:	us-gaap_SecuritiesSoldUnderAgreementsToRepurchase
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant