Derivative Instruments - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Cash collateral received	$ 300	$ 4,800
Return of cash collateral into brokerage accounts	4,300	4,500
Losses on equity options activity	22,200	7,900
Exchange-traded options | Long exchange-traded options
Derivative [Line Items]
Cash collateral received	0	0
Long exchange-trade equity options at fair value	6,900	2,600
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	$ 12,300	$ 3,800