Revenue - Disaggregation of Revenue by Revenue Source and Pattern of Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 123,933	$ 123,738	$ 366,672	$ 351,783
Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	122,093		361,597
Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues	1,840		5,075
Services
Disaggregation of Revenue [Line Items]
Revenues	122,879	117,415	363,986	329,192
Services | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	122,093		361,597
Services | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues	786		2,389
Professional Services
Disaggregation of Revenue [Line Items]
Revenues	118,483		350,368
Professional Services | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	118,483		350,368
Professional Services | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues	0		0
Professional Services | Time and materials contracts
Disaggregation of Revenue [Line Items]
Revenues	85,127		252,158
Professional Services | Time and materials contracts | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	85,127		252,158
Professional Services | Time and materials contracts | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues	0		0
Professional Services | Fixed fee percent complete contracts
Disaggregation of Revenue [Line Items]
Revenues	9,731		26,741
Professional Services | Fixed fee percent complete contracts | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	9,731		26,741
Professional Services | Fixed fee percent complete contracts | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues	0		0
Professional Services | Fixed fee contracts
Disaggregation of Revenue [Line Items]
Revenues	20,402		62,001
Professional Services | Fixed fee contracts | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	20,402		62,001
Professional Services | Fixed fee contracts | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues	0		0
Professional Services | Reimbursable expenses
Disaggregation of Revenue [Line Items]
Revenues	3,223		9,468
Professional Services | Reimbursable expenses | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	3,223		9,468
Professional Services | Reimbursable expenses | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues	0		0
Other Services
Disaggregation of Revenue [Line Items]
Revenues	4,396		13,618
Other Services | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	3,610		11,229
Other Services | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues	786		2,389
Software and hardware
Disaggregation of Revenue [Line Items]
Revenues	1,054	$ 6,323	2,686	$ 22,591
Software and hardware | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues	0		0
Software and hardware | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues	$ 1,054		$ 2,686