Segment Reporting - Financial Information (Details) $ in Thousands	3 Months Ended				6 Months Ended	9 Months Ended
	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($)	Sep. 30, 2016 USD ($) segment	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Segment reporting
Number of operating segments | segment						4
Total Revenues	$ 104,185		$ 120,409			$ 349,463	$ 410,630
Income (loss) before income tax expense (benefit)	(27,798)		3,190			(41,094)	16,581
Accrued settlement costs	22,103					22,103
Identifiable assets	917,102		1,693,817			917,102	1,693,817	$ 1,709,022
Restructuring charge						4,355
Amounts reclassified from accumulated other comprehensive loss	1,066					1,066
Settlement Agreement With S E C Involving Prereleased American Depositary Receipts [Member]
Segment reporting
Accrued settlement costs	22,100					22,100
Legal and related costs	1,600
Chief Executive Officer
Segment reporting
Cash and stock awards	500					3,800
Former CEO
Segment reporting
Net settlement charge					$ 4,800
Insurance recovery	900	$ 500			500	900
Legal and related costs					$ 2,700
Loss of Profits Due to Outage of Outsourced Primary Data Centre
Segment reporting
Proceeds from insurer to settle claims		2,400
Settlement with S E C for Investigation into Proprietary Trading Pilot
Segment reporting
Accrued settlement costs				$ 20,300
Legal and related costs			2,600	$ 2,300
Consolidation of leased facilities
Segment reporting
Restructuring charge		$ 4,400
U.S. Operations
Segment reporting
Total Revenues	48,774		66,039			173,677	221,967
Income (loss) before income tax expense (benefit)	(8,528)		752			(9,297)	17,543
Identifiable assets	418,357		1,263,395			418,357	1,263,395
Canadian Operations
Segment reporting
Total Revenues	13,719		14,899			45,605	50,516
Income (loss) before income tax expense (benefit)	1,496		3,595			7,616	10,964
Identifiable assets	108,647		99,413			108,647	99,413
European Operations
Segment reporting
Total Revenues	28,894		28,899			92,236	99,079
Income (loss) before income tax expense (benefit)	4,709		4,830			16,672	23,723
Identifiable assets	328,731		267,863			328,731	267,863
Asia Pacific Operations
Segment reporting
Total Revenues	12,502		10,351			34,539	38,385
Income (loss) before income tax expense (benefit)	901		(411)			208	2,298
Identifiable assets	61,367		63,146			61,367	63,146
Corporate
Segment reporting
Total Revenues	296		221			3,406	683
Income (loss) before income tax expense (benefit)	(26,376)		$ (5,576)			$ (56,293)	$ (37,947)
Currency translation adjustment
Segment reporting
Amounts reclassified from accumulated other comprehensive loss	$ 1,100