Financial Instruments Owned and Pledged as Collateral at Fair Value, Securities Purchased Under Agreements to Resell and Securities Sold Under Agreements to Repurchase - Summary of Assets, Liabilities and Collateral Received or Pledged (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial Instruments Owned and Pledged as Collateral at Fair Value	$ 13,279	$ 12,431
Securities Purchased Under Agreements to Resell	8,766	13,566
Securities Sold Under Agreements to Repurchase	(22,050)	(26,000)
Asset (Liability) Balance [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial Instruments Owned and Pledged as Collateral at Fair Value	13,279	12,431
Securities Purchased Under Agreements to Resell	8,766	13,566
Total Assets	22,045	25,997
Securities Sold Under Agreements to Repurchase	(22,050)	(26,000)
Market Value of Collateral Received or (Pledged) [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities Purchased Under Agreements to Resell	8,763	13,572
Securities Sold Under Agreements to Repurchase	$ (22,057)	$ (25,992)