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Summary of Significant Accounting Policies - Software Development Costs (Details) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]      
Unamortized software development costs $ 28,512,000 $ 22,240,000 $ 17,490,000
Software development amortization expense 10,843,000 8,258,000 8,123,000
Software development impairment charges 900,000 0 500,000
Intangible assets      
Software development impairment charges $ 900,000 $ 0 $ 500,000
Software and Software Development Costs | Minimum      
Intangible assets      
Finite-Lived Intangible Asset, Useful Life 2 years    
Software and Software Development Costs | Maximum      
Intangible assets      
Finite-Lived Intangible Asset, Useful Life 3 years