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Summary of Significant Accounting Policies - Property, Equipment and Capitalized Software Costs (Details) - USD ($)
$ in Millions
1 Months Ended 12 Months Ended
Feb. 28, 2018
Dec. 31, 2018
Dec. 31, 2017
Corporate Administrative Office Building [Member]      
Property Plant And Equipment [Line Items]      
Carrying value of property     $ 1.6
Proceeds from sale of property $ 1.8    
Minimum [Member]      
Property Plant And Equipment [Line Items]      
Property, equipment and capitalized software, useful life   1 year  
Minimum [Member] | Capitalized Software [Member]      
Property Plant And Equipment [Line Items]      
Property, equipment and capitalized software, useful life   2 years  
Maximum [Member]      
Property Plant And Equipment [Line Items]      
Property, equipment and capitalized software, useful life   30 years  
Maximum [Member] | Capitalized Software [Member]      
Property Plant And Equipment [Line Items]      
Property, equipment and capitalized software, useful life   5 years