Summary of Significant Accounting Policies - Additional Information (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) Segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Contract payment term description									contracts typically contain billing terms that provide for invoicing monthly or upon completion of milestones,  and payment on a net 30-day basis.
Contracts payment, term									30 days
Number of reportable segments | Segment									1
Goodwill, impaired, accumulated impairment loss	$ 0								$ 0
Goodwill, impairment loss									$ 0
Performance based share awards, performance period									3 years
Number of operating segments | Segment									1
Revenue	434,335,000	$ 360,315,000	$ 353,987,000	$ 358,238,000	$ 396,636,000	$ 373,918,000	$ 366,717,000	$ 341,254,000	$ 1,506,875,000	$ 1,478,525,000	$ 1,337,973,000
Foreign financial institutions, actual deposits	81,500,000				$ 7,100,000				81,500,000	7,100,000
Federal Government Agencies And Departments
Summary Of Significant Accounting Policies [Line Items]
Revenue									$ 667,000,000.0	$ 561,000,000.0	$ 546,500,000
Federal Government Agencies And Departments | Customer Concentration Risk | Sales Revenue, Net
Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage									44.00%	38.00%	41.00%
International Clients | Geographic Concentration Risk | Sales Revenue, Net
Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage									13.00%	8.00%	13.00%
International | Long-Lived Assets
Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage									15.00%	17.00%
Indirect and Selling Expenses
Summary Of Significant Accounting Policies [Line Items]
Impairment expense related to intangible assets									$ 3,100,000	$ 1,700,000
Minimum
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful life									2 years
Finite-lived intangible asset, useful life									1 year
Minimum | Other Assets
Summary Of Significant Accounting Policies [Line Items]
Finite-lived intangible asset, useful life									3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful life									7 years
Finite-lived intangible asset, useful life									10 years
Insured domestic bank accounts	$ 250,000								$ 250,000
Maximum | Other Assets
Summary Of Significant Accounting Policies [Line Items]
Finite-lived intangible asset, useful life									5 years