Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 732,164	$ 729,547
Cash restricted or segregated under regulations and other	41,116	6,500
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$ 773,280	$ 736,047	$ 532,887	$ 181,415