Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Cash Flows [Abstract]
Increase (Decrease) in Deposit Assets	$ 28,716	$ 3,717
Cash flows from operating activities
Net income (loss)	6,709	(4,751)
Non-cash items included in net income (loss):
Depreciation and amortization of furniture, equipment and leasehold improvements	1,542	1,432
Deferred income taxes	3,043	807
Amortization of notes receivable	3,205	2,782
Amortization of debt issuance costs	65	121
Provision for (reversal of) credit losses	40	(33)
Share-based compensation	1,484	739
Decrease (increase) in operating assets:
Receivable from brokers, dealers and clearing organizations	15,985	(17,651)
Receivable from customers	(33,755)	17,335
Income tax receivable	(193)	(2,511)
Securities purchased under agreements to resell	658	20,110
Securities owned	(73,030)	(292,599)
Notes receivable	(5,071)	(6,491)
Other assets	21,391	(5,860)
Increase (decrease) in operating liabilities:
Drafts payable	(21,419)	(6,445)
Payable to brokers, dealers and clearing organizations	43,643	(46,185)
Payable to customers	59,178	54,402
Securities sold under agreements to repurchase	(10,461)	78,006
Securities sold but not yet purchased	53,400	214,422
Accrued compensation	(69,340)	(49,200)
Accounts payable and other liabilities	4,099	3,301
Cash used in operating activities	(27,543)	(41,986)
Cash flows from investing activities
Purchase of furniture, equipment and leasehold improvements	(2,696)	(1,550)
Payments to Acquire Intangible Assets	(400)	0
Cash used in investing activities	(3,096)	(1,550)
Cash flows from financing activities
Cash dividends paid on Class A non-voting and Class B voting common stock	(1,456)	(1,480)
Cash dividends paid to non-controlling interest	0	(816)
Repurchase of Class A non-voting common stock for cancellation	0	(4,357)
Payments for employee taxes withheld related to vested share-based awards	(2,444)	(2,203)
Increase in bank call loans, net	29,100	49,900
Cash provided by financing activities	25,200	41,044
Net decrease in cash and cash equivalents	(5,439)	(2,492)
Cash and cash equivalents, beginning of period	48,154	64,913
Cash and cash equivalents, end of period	42,715	62,421
Schedule of non-cash financing activities
Employee share plan issuance	37	3,857
Supplemental disclosure of cash flow information
Cash paid during the period for interest	12,578	2,023
Cash paid during the period for income taxes, net	$ 100	$ 503