Revenue - Disaggregation of Revenue by Revenue Source and Pattern of Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 144,684	$ 123,933	$ 420,368	$ 366,672
Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	143,344	122,093	415,986	361,597
Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues	1,340	1,840	4,382	5,075
Services
Disaggregation of Revenue [Line Items]
Revenues	144,060	122,879	418,160	363,986
Services | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	143,344	122,093	415,986	361,597
Services | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues	716	786	2,174	2,389
Professional Services
Disaggregation of Revenue [Line Items]
Revenues	139,861	118,483	405,634	350,368
Professional Services | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	139,861	118,483	405,634	350,368
Professional Services | Transferred at 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	99,961	85,127	284,423	252,158
Professional Services | Time and materials contracts | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	99,961	85,127	284,423	252,158
Professional Services | Time and materials contracts | Transferred at 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	9,465	9,731	32,337	26,741
Professional Services | Fixed fee percent complete contracts | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	9,465	9,731	32,337	26,741
Professional Services | Fixed fee percent complete contracts | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Professional Services | Fixed fee contracts
Disaggregation of Revenue [Line Items]
Revenues	26,548	20,402	76,683	62,001
Professional Services | Fixed fee contracts | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	26,548	20,402	76,683	62,001
Professional Services | Fixed fee contracts | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Professional Services | Reimbursable expenses
Disaggregation of Revenue [Line Items]
Revenues	3,887	3,223	12,191	9,468
Professional Services | Reimbursable expenses | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	3,887	3,223	12,191	9,468
Professional Services | Reimbursable expenses | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Other Services
Disaggregation of Revenue [Line Items]
Revenues	4,199	4,396	12,526	13,618
Other Services | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	3,483	3,610	10,352	11,229
Other Services | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues	716	786	2,174	2,389
Software and hardware
Disaggregation of Revenue [Line Items]
Revenues	624	1,054	2,208	2,686
Software and hardware | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Software and hardware | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues	$ 624	$ 1,054	$ 2,208	$ 2,686