OPERATING SEGMENTS, Revenues by Client Location (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 174,695	$ 133,184	$ 335,079	$ 257,382
Reimbursable expenses and other revenues
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	1,672	1,510	3,639	2,948
United States
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	75,092	59,746	144,228	117,196
United Kingdom
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	33,176	27,711	67,420	54,779
Switzerland
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	20,833	10,734	41,365	20,014
Russia
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	12,772	13,192	23,162	24,930
Canada
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	11,474	8,393	21,455	13,818
Germany
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	6,360	4,537	12,492	9,070
China
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	3,210	0	3,210	0
Netherlands
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	2,344	2,384	4,462	4,770
Sweden
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	2,167	1,349	4,479	2,604
Kazakhstan
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	1,374	2,028	2,616	4,493
Other Countries
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 4,221	$ 1,600	$ 6,551	$ 2,760