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	Mar. 31, 2019	Dec. 31, 2018
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial Instruments Owned and Pledged as Collateral at Fair Value	$ 16,978	$ 22,349
Securities Purchased Under Agreements to Resell	8,570	2,696
Securities Sold Under Agreements to Repurchase	(25,552)	(25,075)
Asset (Liability) Balance [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial Instruments Owned and Pledged as Collateral at Fair Value	16,978	22,349
Securities Purchased Under Agreements to Resell	8,570	2,696
Total Assets	25,548	25,045
Securities Sold Under Agreements to Repurchase	(25,552)	(25,075)
Market Value of Collateral Received or (Pledged) [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities Purchased Under Agreements to Resell	8,577	2,701
Securities Sold Under Agreements to Repurchase	$ (25,532)	$ (25,099)