Acquisitions - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands						3 Months Ended			9 Months Ended
	Jul. 29, 2019	Apr. 01, 2019	May 18, 2018	May 01, 2018	Apr. 03, 2018	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Business Acquisition [Line Items]
Note payable									$ 550
Goodwill						$ 90,706			90,706		$ 48,382
Purchase price of acquisition, cash									$ 58,419	$ 35,857
Mission Mode
Business Acquisition [Line Items]
Date of acquisition of business		Apr. 01, 2019
Total purchase price		$ 6,800					$ 7,314
Note payable		600					550
Weighted average useful life of identified acquired intangible assets									6 years 10 months 24 days
Goodwill						2,900	2,918		$ 2,900
Business acquisition transaction costs									$ 100
Cash paid							$ 6,764
Mission Mode | Acquired Technology
Business Acquisition [Line Items]
Weighted average useful life of identified acquired intangible assets									3 years
Mission Mode | Customer Relationships
Business Acquisition [Line Items]
Weighted average useful life of identified acquired intangible assets									7 years
Mission Mode | Trade Names
Business Acquisition [Line Items]
Weighted average useful life of identified acquired intangible assets									1 year
Mission Mode | Maximum
Business Acquisition [Line Items]
Contingent payment		$ 1,000
Estimated useful life									7 years
Mission Mode | Minimum
Business Acquisition [Line Items]
Estimated useful life									1 year
NC4 Inc., NC4 Public Sector LLC, and Celerium Group
Business Acquisition [Line Items]
Date of acquisition of business	Jul. 29, 2019
NC4 Inc. and NC4 Public Sector LLC
Business Acquisition [Line Items]
Total purchase price	$ 84,500					84,493
Weighted average useful life of identified acquired intangible assets									5 years 10 months 17 days
Goodwill						40,424			$ 40,424
Business acquisition transaction costs						200			$ 200
Cash paid	$ 51,700
Number of newly issued common stock	320,998
Common stock price per share	$ 102.18
Purchase price of acquisition, cash						$ 51,655
NC4 Inc. and NC4 Public Sector LLC | Acquired Technology
Business Acquisition [Line Items]
Weighted average useful life of identified acquired intangible assets									3 years
NC4 Inc. and NC4 Public Sector LLC | Customer Relationships
Business Acquisition [Line Items]
Weighted average useful life of identified acquired intangible assets									7 years
NC4 Inc. and NC4 Public Sector LLC | Trade Names
Business Acquisition [Line Items]
Weighted average useful life of identified acquired intangible assets									3 years
NC4 Inc. and NC4 Public Sector LLC | Maximum
Business Acquisition [Line Items]
Estimated useful life									7 years
NC4 Inc. and NC4 Public Sector LLC | Minimum
Business Acquisition [Line Items]
Estimated useful life									3 years
UMS
Business Acquisition [Line Items]
Date of acquisition of business					Apr. 03, 2018
Purchase price of acquisition, cash					$ 31,900
PlanetRisk, Inc.
Business Acquisition [Line Items]
Date of acquisition of business				May 01, 2018
Purchase price of acquisition, cash				$ 2,000
Respond B.V.
Business Acquisition [Line Items]
Date of acquisition of business			May 18, 2018
Total purchase price			$ 2,300
Note payable			400
Purchase price of acquisition, cash			$ 2,000
UMS, PlanetRisk, Inc. and Respond B.V.
Business Acquisition [Line Items]
Business acquisition transaction costs								$ 300		$ 600