Summary of Significant Accounting Policies (Expenses and Net Loss Per Share) (Details) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) segment $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) $ / shares shares
Advertising expense
Advertising expense									$ 300	$ 500	$ 300
Segment reporting
Number of operating segments | segment									1
Medical device excise tax
Excise tax on sales (as a percent)									2.30%
Medical device excise tax expense									$ 800	700	400
Numerator for basic and diluted loss per share:
Net loss	$ (14,990)	$ (17,107)	$ (10,892)	$ (14,257)	$ (12,130)	$ (10,396)	$ (10,543)	$ (12,653)	$ (57,246)	$ (45,722)	$ (47,889)
Denominator for basic loss per share:
Weighted average shares | shares									21,993,066	4,239,564	3,996,867
Basic loss per share attributable to ConforMIS, Inc. stockholders (in dollars per share) | $ / shares									$ (2.60)	$ (10.78)	$ (11.98)
Diluted loss per share attributable to ConforMIS, Inc. stockholders (in dollars per share) | $ / shares									$ (2.60)	$ (10.78)	$ (11.98)