Derivative Financial Instruments - Cash deposits (Details) - Zero Cost Collar and Forward Contracts [Member] - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deposit Assets [Line Items]
Deposit with counterparty	$ 1,000	$ 5,250
DB [Member]
Deposit Assets [Line Items]
Deposit with counterparty	0	1,000
NFIK [Member]
Deposit Assets [Line Items]
Deposit with counterparty	0	3,250
SC [Member]
Deposit Assets [Line Items]
Deposit with counterparty	$ 1,000	$ 1,000

The amount of cash or securities placed with a broker or counterparty as security for a trading or derivatives securities position which was partially obtained with funds provided by the broker dealer.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.8,17)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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