Income Taxes - Tax credit carry forwards and of Investments in Foreign Subsidiaries (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Tax credit carryforwards
Common stock, shares issued	28,372,634	27,953,233
Iinvestments in foreign subsidiaries	$ 37.2
Research and development credits \| Federal
Tax credit carryforwards
Research and development tax credit carryforwards	6.8
Research and development credits \| State
Tax credit carryforwards
Research and development tax credit carryforwards	$ 3.9

Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Amount of undistributed earnings of foreign subsidiaries intended to be permanently reinvested outside the country of domicile.

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