Offsetting Assets and Liabilities (Narrative) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Offsetting [Abstract]
Fair value of financial instruments pledged against the repurchase agreements and other advances	$ 3,800,000	$ 4,200,000
Fair value of securities pledged against the swaps	$ 0	$ 0

Fair value of securities pledged as collateral against securities sold under agreement to repurchase.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226013-175313

Name:	us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseFairValueOfCollateral
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant