Summary of Significant Accounting Policies - Deferred Implementation Costs, Deferred Solution and Other Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Deferred Implementation Costs
Capitalized Contract Cost [Line Items]
Capitalization of implementation costs	$ 3.5	$ 4.1
Amortization of capitalized implementation costs	$ 2.7	2.1
Deferred Implementation Costs | Minimum
Capitalized Contract Cost [Line Items]
Expected period of customer benefit	5 years
Deferred Implementation Costs | Maximum
Capitalized Contract Cost [Line Items]
Expected period of customer benefit	7 years
Deferred Commissions
Capitalized Contract Cost [Line Items]
Capitalization of implementation costs	$ 3.1	5.6
Amortization of capitalized implementation costs	$ 3.4	$ 1.8
Deferred Commissions | Minimum
Capitalized Contract Cost [Line Items]
Expected period of customer benefit	5 years
Deferred Commissions | Maximum
Capitalized Contract Cost [Line Items]
Expected period of customer benefit	7 years