OPERATING SEGMENTS, Revenues by Client Location (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 192,764	$ 140,150	$ 527,843	$ 397,532
Reimbursable expenses and other revenues
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	2,463	2,186	6,102	5,134
United States
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	84,276	62,871	228,504	180,067
United Kingdom
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	35,222	26,637	102,642	81,416
Switzerland
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	22,508	13,920	63,873	33,934
Russia
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	14,351	11,534	37,513	36,464
Canada
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	13,518	9,162	34,973	22,980
Germany
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	6,459	5,141	18,951	14,211
China
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	5,058	0	8,268	0
Netherlands
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	2,174	1,895	6,636	6,665
Sweden
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	1,734	1,382	6,213	3,986
Kazakhstan
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	525	2,921	3,141	7,414
Other locations
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 4,476	$ 2,501	$ 11,027	$ 5,261