Derivative Instruments - Collateral (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Derivative Instruments
Collateral held by third parties	$ 2.1	$ 2.7

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5624258-113959

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