Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Flows from Operating Activities:
Net (loss) income	$ (39,440)	$ (25,918)	$ 91,570
Adjustments to reconcile net (loss) income to net cash used in operating activities:
Gain on sale of investment research operations		(21)	(107,699)
Depreciation and amortization	45,153	43,523	44,151
Deferred income tax expense (benefit)	33,826	(15,755)	12,912
Provision for doubtful accounts	375	67	496
Non-cash share-based compensation	20,238	25,620	16,667
Leasehold asset write-off	7,492
Other intangible asset impairment	325
Changes in operating assets and liabilities:
Cash restricted or segregated under regulations and other	22,334	(3,048)	55
Deposits with clearing organizations	8,661	1,420	(1,113)
Securities owned, at fair value	1,004	3,048	5,973
Receivables from brokers, dealers and clearing organizations	(26,701)	871,317	(404,818)
Receivables from customers	(11,832)	(11,738)	53,909
Accounts payable and accrued expenses	(11,292)	13,034	(18,978)
Payables to brokers, dealers and clearing organizations	7,658	(853,923)	366,462
Payables to customers	7,907	2,681	(775)
Securities sold, not yet purchased, at fair value	(247)	(2,397)	(5,102)
Income taxes receivable/payable	2,892	(11,889)	1,710
Excess tax benefit from share-based payment arrangements		(880)	(2,982)
Other, net	(339)	(59)	(3,692)
Net cash provided by operating activities	68,014	35,082	48,746
Cash Flows from Investing Activities:
Proceeds from sale of investment research operations, net of deal costs		6,125	111,240
Capital purchases	(19,402)	(21,315)	(11,905)
Capitalization of software development costs	(27,782)	(24,617)	(26,003)
Net cash (used in) provided by investing activities	(47,184)	(39,807)	73,332
Cash Flows from Financing Activities:
Repayments of long term debt	(3,963)	(6,200)	(8,820)
Proceeds from (repayments of) borrowing under short-term bank loans	29,272	(9,784)	3,573
Debt issuance costs	(762)	(810)
Excess tax benefit from share-based payment arrangements		880	2,982
Common stock issued	1,376	3,743	1,742
Common stock repurchased	(16,933)	(22,112)	(42,046)
Dividends paid	(9,156)	(9,124)	(7,030)
Shares withheld for net settlements of share-based awards	(10,779)	(6,795)	(8,978)
Net cash used in financing activities	(10,945)	(50,202)	(58,577)
Effect of exchange rate changes on cash and cash equivalents	(410)	2,251	(8,058)
Net increase (decrease) in cash and cash equivalents	9,475	(52,676)	55,443
Cash and cash equivalents - beginning of period	277,977	330,653	275,210
Cash and cash equivalents - end of period	287,452	277,977	330,653
Supplemental cash flow information:
Interest paid	4,960	6,116	3,607
Income taxes paid	10,515	$ 9,880	15,098
Supplemental disclosure of non-cash investing and financing activities:
Capital expenditures funded by financing from seller	$ 400		$ 3,606