OPERATING SEGMENTS, Revenues by Client Location (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 160,384	$ 124,198
Reimbursable expenses and other revenues [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	1,967	1,438
United States [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	69,136	57,450
United Kingdom [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	34,244	27,068
Switzerland [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	20,532	9,280
Russia [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	10,390	11,738
Canada [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	9,981	5,425
Germany [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	6,132	4,533
Sweden [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	2,312	1,255
Netherlands [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	2,118	2,386
Kazakhstan [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	1,242	2,465
Belgium [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	641	0
France [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	373	0
Italy [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	223	9
Norway [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	189	0
Ukraine [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	165	188
Spain [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	106	632
Other Countries [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 633	$ 331