Summary of Significant Accounting Policies - Foreign Currency (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Summary of Significant Accounting Policies
Foreign exchange gains (losses) realized	$ 1.4	$ (0.6)	$ (1.3)

Amount before tax of foreign currency transaction realized gain (loss) recognized in the income statement.

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