Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Product sales, net	$ 31,020	$ 30,499	$ 77,712	$ 78,460
Other revenue	1,238	0	1,238	0
Total revenue	32,258	30,499	78,950	78,460
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
Disaggregation of Revenue [Line Items]
Product sales, net	8	656	695	353
MACI Implants and Kits, and Epicel
Disaggregation of Revenue [Line Items]
Product sales, net	31,020	30,499	77,712	78,460
Through Intermediary | Implants | Contract rate
Disaggregation of Revenue [Line Items]
Product sales, net	14,897	11,779	36,084	34,555
Through Intermediary | Implants | Time-and-materials contract
Disaggregation of Revenue [Line Items]
Product sales, net	3,529	4,030	10,299	10,584
Time-and-materials contract | Implants | Time-and-materials contract
Disaggregation of Revenue [Line Items]
Product sales, net	782	573	1,793	1,176
Provider or Facility | Implants | Contract rate
Disaggregation of Revenue [Line Items]
Product sales, net	4,602	3,039	9,528	9,715
Provider or Facility | Other
Disaggregation of Revenue [Line Items]
Other revenue	1,238	0	1,238	0
Directly to consumer | Biopsy kits
Disaggregation of Revenue [Line Items]
Product sales, net	539	533	1,348	1,632
Directly to consumer | Epicel
Disaggregation of Revenue [Line Items]
Product sales, net	$ 6,663	$ 9,889	$ 17,965	$ 20,445