Revenue - Disaggregation of Revenue by Revenue Source and Pattern of Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 141,869	$ 121,798	$ 275,684	$ 242,739
Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	140,367	120,128	272,642	239,505
Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues	1,502	1,670	3,042	3,234
Services
Disaggregation of Revenue [Line Items]
Revenues	141,234	120,912	274,100	241,107
Services | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	140,367	120,128	272,642	239,505
Services | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues	867	784	1,458	1,602
Professional Services
Disaggregation of Revenue [Line Items]
Revenues	136,843	116,374	265,773	231,887
Professional Services | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	136,843	116,374	265,773	231,887
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	96,084	84,884	184,462	167,033
Professional Services | Time and materials contracts | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	96,084	84,884	184,462	167,033
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	10,414	7,898	22,872	17,010
Professional Services | Fixed fee percent complete contracts | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	10,414	7,898	22,872	17,010
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	25,955	20,377	50,135	41,599
Professional Services | Fixed fee contracts | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	25,955	20,377	50,135	41,599
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	4,390	3,215	8,304	6,245
Professional Services | Reimbursable expenses | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	4,390	3,215	8,304	6,245
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	4,391	4,538	8,327	9,220
Other Services | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	3,524	3,754	6,869	7,618
Other Services | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues	867	784	1,458	1,602
Software and hardware
Disaggregation of Revenue [Line Items]
Revenues	635	886	1,584	1,632
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	$ 635	$ 886	$ 1,584	$ 1,632