Segment and Related Information - Revenue by Geographic Region (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) segment	Jun. 30, 2019 USD ($)
Consulting Fee Revenue and Total Revenue by Geographic Region:
Number of reporting units | segment			1
Total revenue	$ 94,449	$ 98,257	$ 187,757	$ 196,940
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	$ 49,785	$ 51,336	$ 95,805	$ 99,438
Percent of Total Revenue	52.70%	52.30%	51.00%	50.60%
Latin America
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	$ 659	$ 1,911	$ 1,830	$ 4,345
Percent of Total Revenue	0.70%	1.90%	1.00%	2.20%
Europe
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	$ 14,432	$ 10,622	$ 25,969	$ 21,956
Percent of Total Revenue	15.30%	10.80%	13.80%	11.10%
Middle East
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	$ 21,529	$ 25,972	$ 46,101	$ 54,283
Percent of Total Revenue	22.80%	26.40%	24.50%	27.60%
Africa
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	$ 7,258	$ 6,930	$ 14,555	$ 13,879
Percent of Total Revenue	7.70%	7.10%	7.80%	7.00%
Asia/Pacific
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	$ 786	$ 1,486	$ 3,497	$ 3,039
Percent of Total Revenue	0.80%	1.50%	1.90%	1.50%
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	52.70%	52.20%	51.00%	50.60%
Geographic Concentration Risk | Latin America
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	0.70%	1.90%	1.00%	2.20%
Geographic Concentration Risk | Europe
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	15.30%	10.80%	13.80%	11.10%
Geographic Concentration Risk | Middle East
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	22.80%	26.50%	24.50%	27.60%
Geographic Concentration Risk | Africa
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	7.70%	7.10%	7.80%	7.00%
Geographic Concentration Risk | Asia/Pacific
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	0.80%	1.50%	1.90%	1.50%
Consulting fee revenue
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	$ 75,760	$ 77,035	$ 152,910	$ 156,035
Consulting fee revenue | United States
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	34,690	34,199	68,734	66,794
Consulting fee revenue | Latin America
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	659	1,914	1,830	4,343
Consulting fee revenue | Europe
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	11,067	10,182	21,648	21,084
Consulting fee revenue | Middle East
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	21,639	23,075	45,052	48,335
Consulting fee revenue | Africa
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	6,564	6,366	13,166	12,777
Consulting fee revenue | Asia/Pacific
Consulting Fee Revenue and Total Revenue by Geographic Region:
Total revenue	$ 1,141	$ 1,299	$ 2,480	$ 2,702
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	45.80%	44.30%	45.00%	42.80%
Consulting fee revenue | Geographic Concentration Risk | Latin America
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	0.90%	2.50%	1.20%	2.80%
Consulting fee revenue | Geographic Concentration Risk | Europe
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	14.60%	13.20%	14.20%	13.50%
Consulting fee revenue | Geographic Concentration Risk | Middle East
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	28.50%	30.00%	29.40%	31.00%
Consulting fee revenue | Geographic Concentration Risk | Africa
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	8.70%	8.30%	8.60%	8.20%
Consulting fee revenue | Geographic Concentration Risk | Asia/Pacific
Consulting Fee Revenue and Total Revenue by Geographic Region:
Percent of Total Revenue	1.50%	1.70%	1.60%	1.70%