Receivables from and payables to brokers, dealers and clearing organizations (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Brokers and Dealers [Abstract]
Receivable from Broker-dealers	$ 621,271	$ 623,523
Securities Failed-to-Deliver	98,810	45,673
Clearing organizations	46,345	3,180
Securities borrowed interest receivable	6,891	9,319
Receivable from brokers, dealers and clearing organizations	773,317	681,695
Payable to Broker-Dealers	92,103	185,838
Securities Failed-to-Receive	153,133	57,580
Clearing organizations	78,546	18,063
Securities loaned interest payable	6,314	9,537
Payables to brokers, dealers and clearing organizations	$ 330,096	$ 271,018