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	Dec. 31, 2018	Dec. 31, 2017
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial Instruments Owned and Pledged as Collateral at Fair Value	$ 22,349	$ 19,374
Securities Purchased Under Agreements to Resell	2,696	10,645
Securities Sold Under Agreements to Repurchase	(25,075)	(30,027)
Asset (Liability) Balance [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial Instruments Owned and Pledged as Collateral at Fair Value	22,349	19,374
Securities Purchased Under Agreements to Resell	2,696	10,645
Total Assets	25,045	30,019
Securities Sold Under Agreements to Repurchase	(25,075)	(30,027)
Market Value of Collateral Received or (Pledged) [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities Purchased Under Agreements to Resell	2,701	10,643
Securities Sold Under Agreements to Repurchase	$ (25,099)	$ (30,020)