Related-Party Transactions - Acquisitions from Consolidated RMBS Trusts (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
RMBS
Related-Party Transactions
Payments to acquire marketable securities	$ 524.5	$ 176.6

Amount of cash outflow for purchase of marketable security.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=124260329&loc=d3e26853-111562

Name:	us-gaap_PaymentsToAcquireMarketableSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration