Receivables from and payables to brokers, dealers and clearing organizations (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Brokers and Dealers [Abstract]
Receivable from Broker-dealers	$ 623,523	$ 692,581
Securities Failed-to-Deliver	45,673	72,918
Clearing organizations	3,180	15,319
Securities borrowed interest receivable	9,319	5,295
Receivable from brokers, dealers and clearing organizations	681,695	786,113
Payable to Broker-Dealers	185,838	159,443
Securities Failed-to-Receive	57,580	28,826
Clearing organizations	18,063	36,338
Securities loaned interest payable	9,537	4,124
Payables to brokers, dealers and clearing organizations	$ 271,018	$ 228,731