Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Statement of Cash Flows [Abstract]
Payments of Debt Issuance Costs	$ 0	$ (547)
Increase (Decrease) in Deposit Assets	14,642	2,500
Cash flows from operating activities
Net income (loss)	15,548	(6,061)
Non-cash items included in net income (loss):
Depreciation and amortization of furniture, equipment and leasehold improvements	3,140	2,783
Deferred income taxes	2,712	1,325
Amortization of notes receivable	6,378	5,756
Amortization of debt issuance costs	129	223
Write off of Deferred Debt Issuance Cost	0	430
Provision for (reversal of) credit losses	79	(4)
Share-based compensation	5,216	1,715
Decrease (increase) in operating assets:
Receivable from brokers, dealers and clearing organizations	(17,412)	(9,772)
Receivable from customers	12,439	(26,425)
Income tax receivable	121	(4,289)
Securities purchased under agreements to resell	(6,080)	19,154
Securities owned	(93,807)	(279,324)
Notes receivable	(8,268)	(11,897)
Other assets	29,464	(9,317)
Increase (decrease) in operating liabilities:
Drafts payable	(20,780)	(9,461)
Payable to brokers, dealers and clearing organizations	71,059	18,189
Payable to customers	(12,243)	48,616
Securities sold under agreements to repurchase	12,673	79,725
Securities sold but not yet purchased	67,556	149,728
Accrued compensation	(46,251)	(30,925)
Accounts payable and other liabilities	4,280	(8,054)
Cash provided by (used in) operating activities	11,311	(70,385)
Cash flows from investing activities
Purchase of furniture, equipment and leasehold improvements	(3,947)	(2,075)
Purchase of tangible assets	(400)	0
Proceeds from settlement of company-owned life insurance	0	1,194
Cash used in investing activities	(4,347)	(881)
Cash flows from financing activities
Cash dividends paid on Class A non-voting and Class B voting common stock	(2,913)	(2,940)
Cash dividends paid to non-controlling interest	0	(816)
Repurchase of Class A non-voting common stock for cancellation	0	(5,159)
Payments for employee taxes withheld related to vested share-based awards	(2,444)	(2,203)
(Decrease) Increase in bank call loans, net	(10,800)	84,600
Cash (used in) provided by financing activities	(16,157)	122,935
Net (decrease) increase in cash and cash equivalents	(9,193)	51,669
Cash and cash equivalents, beginning of period	48,154	64,913
Cash and cash equivalents, end of period	38,961	116,582
Schedule of non-cash financing activities
Employee share plan issuance	333	3,857
Supplemental disclosure of cash flow information
Cash paid during the period for interest	26,899	14,607
Cash paid during the period for income taxes, net	3,918	551
Proceeds from Issuance of Senior Long-term Debt	0	200,000
Early Repayment of Senior Debt	$ 0	$ 150,000