Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from Operating Activities:
Net income	$ 91,570	$ 50,892	$ 31,085
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on sale of energy research business	(107,699)
Depreciation and amortization	44,151	49,384	53,606
Deferred income tax expense (benefit)	12,912	(4,979)	3,051
Provision for doubtful accounts	496	(801)	(405)
Share-based compensation	16,667	15,359	13,539
Fixed asset disposal			649
Non-cash restructuring charges, net			357
Goodwill and other asset impairment			101
Changes in operating assets and liabilities:
Cash restricted or segregated under regulations and other	55	(616)	(9,491)
Deposits with clearing organizations	(1,113)	38,347	(45,622)
Securities owned, at fair value	5,973	(5,489)	2,445
Receivables from brokers, dealers and clearing organizations	(404,818)	211,491	43,612
Receivables from customers	53,909	(37,238)	(63,376)
Accounts payable and accrued expenses	(18,978)	27,389	9,936
Payables to brokers, dealers and clearing organizations	366,462	(203,805)	(48,338)
Payables to customers	(775)	(5,075)	42,828
Securities sold, not yet purchased, at fair value	(5,102)	6,162	(2,086)
Income taxes receivable/payable	1,710	6,194	12,148
Excess tax benefit	(2,982)	(1,278)	(510)
Other, net	(3,692)	(3,397)	1,663
Net cash provided by operating activities	48,746	142,540	45,192
Cash flows from Investing Activities:
Proceeds from sale of energy research business, net of deal costs	111,240
Investment in unconsolidated affiliates		(2,669)	(474)
Acquisition of subsidiaries and minority interests, net of cash acquired		(18,293)
Capital purchases	(11,905)	(13,798)	(33,549)
Capitalization of software development costs	(26,003)	(26,331)	(22,579)
Net cash provided by (used in) investing activities	73,332	(61,091)	(56,602)
Cash flows from Financing Activities:
Repayments of term loans	(8,820)	(12,551)	(9,505)
Proceeds of short-term bank loans, net	3,573	4,821	51,385
Proceeds from sales-lease back transactions			20,565
Excess tax benefit	2,982	1,278	510
Debt issuance costs		(1,200)
Common stock issued	1,742	96	177
Common stock repurchased	(42,046)	(48,165)	(28,169)
Dividends paid	(7,030)
Shares withheld for net settlements of share-based awards	(8,978)	(6,231)	(4,532)
Net cash (used in) provided by financing activities	(58,577)	(61,952)	30,431
Effect of exchange rate changes on cash and cash equivalents	(8,058)	(6,184)	(2,999)
Net increase in cash and cash equivalents	55,443	13,313	16,022
Cash and cash equivalents - beginning of year	275,210	261,897	245,875
Cash and cash equivalents - end of year	330,653	275,210	261,897
Supplemental cash flow information:
Interest paid	3,607	3,979	3,343
Income taxes paid (refunded)	15,098	$ 11,909	$ (4,079)
Supplemental disclosure of non-cash investing and financing activities:
Capital expenditures funded by financing from seller	$ 3,606