Revenues - Disaggregation of Revenue Source and Pattern of Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenues	$ 131,702	$ 123,933	$ 121,798	$ 120,942	$ 133,478	$ 123,738	$ 117,026	$ 111,019	$ 498,375	$ 485,261	$ 486,982
Transferred Over Time
Disaggregation of Revenue [Line Items]
Revenues									490,478
Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues									7,897
Services
Disaggregation of Revenue [Line Items]
Revenues									494,001	446,619	437,028
Services | Transferred Over Time
Disaggregation of Revenue [Line Items]
Revenues									490,478
Services | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues									3,523
Professional Services
Disaggregation of Revenue [Line Items]
Revenues									475,664
Professional Services | Transferred Over Time
Disaggregation of Revenue [Line Items]
Revenues									475,664
Professional Services | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues									0
Professional Services | Time and materials contracts
Disaggregation of Revenue [Line Items]
Revenues									339,708
Professional Services | Time and materials contracts | Transferred Over Time
Disaggregation of Revenue [Line Items]
Revenues									339,708
Professional Services | Time and materials contracts | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues									0
Professional Services | Fixed fee percent complete contracts
Disaggregation of Revenue [Line Items]
Revenues									38,234
Professional Services | Fixed fee percent complete contracts | Transferred Over Time
Disaggregation of Revenue [Line Items]
Revenues									38,234
Professional Services | Fixed fee percent complete contracts | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues									0
Professional Services | Fixed fee contracts
Disaggregation of Revenue [Line Items]
Revenues									84,374
Professional Services | Fixed fee contracts | Transferred Over Time
Disaggregation of Revenue [Line Items]
Revenues									84,374
Professional Services | Fixed fee contracts | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues									0
Professional Services | Reimbursable expenses
Disaggregation of Revenue [Line Items]
Revenues									13,348
Professional Services | Reimbursable expenses | Transferred Over Time
Disaggregation of Revenue [Line Items]
Revenues									13,348
Professional Services | Reimbursable expenses | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues									0
Other Services
Disaggregation of Revenue [Line Items]
Revenues									18,337
Other Services | Transferred Over Time
Disaggregation of Revenue [Line Items]
Revenues									14,814
Other Services | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues									3,523
Software and hardware
Disaggregation of Revenue [Line Items]
Revenues									4,374	$ 38,642	$ 49,954
Software and hardware | Transferred Over Time
Disaggregation of Revenue [Line Items]
Revenues									0
Software and hardware | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues									$ 4,374