Summary of Significant Accounting Policies (Expenses and Net Loss Per Share) (Details) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020 USD ($) $ / shares shares	Jun. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2020 USD ($) segment $ / shares shares	Jun. 30, 2019 USD ($) $ / shares shares
Advertising expense
Advertising expense	$ 100	$ 100	$ 300	$ 200
Segment reporting
Number of operating segments \| segment			1
Income taxes
Income tax provision	(28)	23	$ (3)	14
Interest and penalties accrued	42	47	42	47
Numerator for basic and diluted loss per share:
Net loss	$ (2,135)	$ (6,763)	$ (11,488)	$ (14,344)
Denominator for basic loss per share:
Basic and diluted weighted average shares \| shares	68,187,128	63,333,737	67,885,622	63,092,874
Basic and diluted loss per share attributable to ConforMIS, Inc. stockholders (in dollars per share) \| $ / shares	$ (0.03)	$ (0.11)	$ (0.17)	$ (0.23)

Amount charged to advertising expense for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line.

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