Revenue - Disaggregation of Revenue by Revenue Source and Pattern of Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 157,678	$ 144,684	$ 449,579	$ 420,368
Over Time
Disaggregation of Revenue [Line Items]
Revenues	156,218	143,344	446,297	415,986
Point In Time
Disaggregation of Revenue [Line Items]
Revenues	1,460	1,340	3,282	4,382
Services
Disaggregation of Revenue [Line Items]
Revenues	156,755	144,060	447,993	418,160
Services | Over Time
Disaggregation of Revenue [Line Items]
Revenues	156,218	143,344	446,297	415,986
Services | Point In Time
Disaggregation of Revenue [Line Items]
Revenues	537	716	1,696	2,174
Professional services
Disaggregation of Revenue [Line Items]
Revenues	152,850	139,861	435,983	405,634
Professional services | Over Time
Disaggregation of Revenue [Line Items]
Revenues	152,850	139,861	435,983	405,634
Professional services | Point In Time
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Professional services | Time and materials contracts
Disaggregation of Revenue [Line Items]
Revenues	114,581	99,961	316,866	284,423
Professional services | Time and materials contracts | Over Time
Disaggregation of Revenue [Line Items]
Revenues	114,581	99,961	316,866	284,423
Professional services | Time and materials contracts | Point In Time
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Professional services | Fixed fee percent complete contracts
Disaggregation of Revenue [Line Items]
Revenues	13,920	9,465	39,556	32,337
Professional services | Fixed fee percent complete contracts | Over Time
Disaggregation of Revenue [Line Items]
Revenues	13,920	9,465	39,556	32,337
Professional services | Fixed fee percent complete contracts | Point In Time
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Professional services | Fixed fee contracts
Disaggregation of Revenue [Line Items]
Revenues	22,836	26,548	72,124	76,683
Professional services | Fixed fee contracts | Over Time
Disaggregation of Revenue [Line Items]
Revenues	22,836	26,548	72,124	76,683
Professional services | Fixed fee contracts | Point In Time
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Professional services | Reimbursable expenses
Disaggregation of Revenue [Line Items]
Revenues	1,513	3,887	7,437	12,191
Professional services | Reimbursable expenses | Over Time
Disaggregation of Revenue [Line Items]
Revenues	1,513	3,887	7,437	12,191
Professional services | Reimbursable expenses | Point In Time
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Other services
Disaggregation of Revenue [Line Items]
Revenues	3,905	4,199	12,010	12,526
Other services | Over Time
Disaggregation of Revenue [Line Items]
Revenues	3,368	3,483	10,314	10,352
Other services | Point In Time
Disaggregation of Revenue [Line Items]
Revenues	537	716	1,696	2,174
Software and hardware
Disaggregation of Revenue [Line Items]
Revenues	923	624	1,586	2,208
Software and hardware | Over Time
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Software and hardware | Point In Time
Disaggregation of Revenue [Line Items]
Revenues	$ 923	$ 624	$ 1,586	$ 2,208