Derivative Instruments - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Cash collateral received	$ 400	$ 300
Return of cash collateral into brokerage accounts	6,400	4,300
Losses on equity options activity	11,900	22,200
Exchange-traded options | Long exchange-traded options
Derivative [Line Items]
Cash collateral received	0	0
Long exchange-trade equity options at fair value	7,500	6,900
Exchange-traded options | Short exchange-traded options
Derivative [Line Items]
Return of cash collateral into brokerage accounts	0	0
Short exchange-traded equity options at fair value	$ 12,500	$ 12,300