Summary of Significant Accounting Policies - Concentration of Credit Risk (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Concentration of Credit Risk
Allowance for doubtful accounts	$ 3.0	$ 3.4
Customer concentration \| Accounts receivable
Concentration of Credit Risk
Risk percentage	10.00%	10.00%
Customer concentration \| Revenue
Concentration of Credit Risk
Risk percentage	10.00%	10.00%	10.00%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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