Segment and Related Information - Revenue by Geographic Region (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)
Consulting Fee Revenue and Total Revenue by Geographic Region:
Number of reporting units | segment			1
Total revenue	$ 88,652	$ 95,670	$ 276,409	$ 292,610
Percent of Total Revenue	100.00%	100.00%	100.00%	100.00%
United States
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	$ 47,721	$ 49,936	$ 143,526	$ 149,374
Percent of Total Revenue	53.90%	52.30%	52.00%	51.10%
Latin America
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	$ 474	$ 1,669	$ 2,304	$ 6,014
Percent of Total Revenue	0.50%	1.70%	0.80%	2.10%
Europe
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	$ 11,465	$ 10,556	$ 37,434	$ 32,512
Percent of Total Revenue	12.90%	11.00%	13.50%	11.10%
Middle East
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	$ 21,024	$ 25,447	$ 67,125	$ 79,730
Percent of Total Revenue	23.70%	26.60%	24.30%	27.20%
Africa
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	$ 6,263	$ 7,005	$ 20,818	$ 20,884
Percent of Total Revenue	7.10%	7.30%	7.50%	7.10%
Asia/Pacific
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	$ 1,705	$ 1,057	$ 5,202	$ 4,096
Percent of Total Revenue	1.90%	1.10%	1.90%	1.40%
Geographic Concentration Risk
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	100.00%	100.00%	100.00%	100.00%
Geographic Concentration Risk | United States
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	53.90%	52.30%	52.00%	51.10%
Geographic Concentration Risk | Latin America
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	0.50%	1.70%	0.80%	2.10%
Geographic Concentration Risk | Europe
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	12.90%	11.00%	13.50%	11.10%
Geographic Concentration Risk | Middle East
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	23.70%	26.60%	24.30%	27.20%
Geographic Concentration Risk | Africa
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	7.10%	7.30%	7.50%	7.10%
Geographic Concentration Risk | Asia/Pacific
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	1.90%	1.10%	1.90%	1.40%
Consulting fee revenue
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	$ 71,543	$ 75,747	$ 224,453	$ 231,782
Consulting fee revenue | United States
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	33,223	33,442	101,957	100,236
Consulting fee revenue | Latin America
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	474	1,668	2,304	6,011
Consulting fee revenue | Europe
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	10,549	9,989	32,197	31,073
Consulting fee revenue | Middle East
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	20,817	23,328	65,869	71,663
Consulting fee revenue | Africa
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	5,588	6,421	18,754	19,198
Consulting fee revenue | Asia/Pacific
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	$ 892	$ 899	$ 3,372	$ 3,601
Consulting fee revenue | Geographic Concentration Risk
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	100.00%	100.00%	100.00%	100.00%
Consulting fee revenue | Geographic Concentration Risk | United States
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	46.50%	44.10%	45.40%	43.20%
Consulting fee revenue | Geographic Concentration Risk | Latin America
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	0.70%	2.20%	1.10%	2.60%
Consulting fee revenue | Geographic Concentration Risk | Europe
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	14.70%	13.20%	14.30%	13.40%
Consulting fee revenue | Geographic Concentration Risk | Middle East
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	29.10%	30.80%	29.30%	30.90%
Consulting fee revenue | Geographic Concentration Risk | Africa
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	7.80%	8.50%	8.40%	8.30%
Consulting fee revenue | Geographic Concentration Risk | Asia/Pacific
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	1.20%	1.20%	1.50%	1.60%