Fixed Assets - Schedule of Property, Plant, and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Cost	$ 213,905	$ 183,510
Accumulated Depreciation	(123,599)	(105,133)
Net Book Value	90,306	78,377
Computers, furniture and fixtures [Member]
Property, Plant and Equipment [Line Items]
Cost	101,806	91,909
Accumulated Depreciation	(74,429)	(64,030)
Net Book Value	27,377	27,879
Leasehold Improvements
Property, Plant and Equipment [Line Items]
Cost	112,099	91,601
Accumulated Depreciation	(49,170)	(41,103)
Net Book Value	$ 62,929	$ 50,498