Revenues by Client Location (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 110,078	$ 86,423	$ 308,261	$ 239,401
Reimbursable expenses and other revenues
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	1,393	1,506	4,186	4,312
United States
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	50,365	41,775	145,629	118,419
United Kingdom
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	25,651	19,307	70,777	50,267
Russia
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	10,554	11,229	29,045	31,041
Switzerland
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	8,496	3,781	21,438	11,153
Germany
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	4,325	1,947	11,766	5,029
Canada
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	3,270	609	5,816	882
Kazakhstan
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	2,967	1,946	6,300	5,600
Ukraine
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	181	661	4,556	1,506
Sweden
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	1,006	1,221	3,478	3,958
Netherlands
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	750	925	2,408	3,189
Other Countries
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 1,120	$ 1,516	$ 2,862	$ 4,045