Revenue	3 Months Ended
Mar. 31, 2017
Risks and Uncertainties [Abstract]
Revenue	Revenue Revenue Recognition and Net Product Sales Total revenues are comprised of product sales of Carticel, Epicel, MACI, bone marrow and surgical kits. Revenue is recognized when persuasive evidence of an arrangement exists, the goods are shipped or delivered, depending on shipping terms, title and risk of loss pass to the customer and collectability is reasonably assured. Shipping and handling costs are included as a component of revenue. On June 30, 2016, the Company reduced the scope of the agreement with its exclusive distributor by terminating their services with respect to a significant portion of its Carticel sales. Prior to June 30, 2016, the distributor purchased and took title to Carticel upon shipment of the product and assumed credit and collection risk. The distributor worked with the payers on behalf of patients and surgeons to ensure medical coverage and to obtain reimbursement for Carticel implantation procedures. The Company retained all responsibility for shipment of the product to the surgical suite. In addition, revenue for Carticel was recorded net of a provision for rebates and cash discounts. These rebates and cash discounts were established by the Company at the time of sale, based on historical experience adjusted to reflect known changes in the factors that impact such reserves. For instance, the distributor of Carticel was entitled to chargeback incentives for services that are provided for based on the selling price to the end customer, under specific contractual arrangements. Cash discounts could also be granted for prompt payment. Effective as of July 1, 2016, the Company transitioned to a direct sales model whereby the Company retains credit and collection risk from the end customer. The Company currently utilizes Dohmen Life Science Services, LLC (DLSS) to provide patient support services and reimbursement services, but this provider does not purchase and take title to Carticel or MACI. The Company - also utilizes Vital Care, Inc. to provide data reporting services and to purchase, bill and collect from certain payers for Carticel and MACI. The Company recognizes product revenues from sales of Carticel and MACI upon delivery to patients as long as (i) there is persuasive evidence that an arrangement exists between ourselves and the customer, (ii) collectability is reasonably assured and (iii) the price is fixed or determinable. Prior authorization or confirmation of coverage level by the patient’s private insurance plan, hospital or government payer is a prerequisite to the shipment of product to a patient. The Company's net product revenues are calculated by estimating expected payments for insurance, hospital or patient payments at the time it recognizes the gross revenue. The estimates are updated prospectively as new information becomes available. In April 2017, the Company received notification from one of our services providers, Vital Care, Inc., of a contractual dispute between Vital Care, Inc. and the third-party payer related to certain of its insurance reimbursement claims associated with Carticel and MACI surgeries performed in 2016 and the first quarter of 2017. Vital Care, Inc. is attempting to resolve this matter with the payer, which may include appealing or resubmitting the claims. While the Company believes reimbursement will be obtained, the ultimate amount of reimbursement may be lower than initially estimated. During the three months ended March 31, 2017, the Company recorded a change in estimate for revenue reserves of $2.1 million related to 2016 sales and $0.7 million related to 2017 sales to reflect the lower reimbursement that would be obtained if the claims are ultimately required to be treated as out-of-network. In addition, the contractual dispute could impact amounts previously collected and certain amounts may need to be repaid while the matter is being resolved; therefore our liquidity may be negatively impacted. As a result of the continuing evaluation and assessment of these expected payments, our estimates for expected payments could change. Concentration of Credit Risk Revenue from one customer, the distributor in the U.S., represented approximately 63% of total revenue during the three months ended March 31, 2016. The next largest customer represented 16% and 13% total revenue during the three months ended March 31, 2017 and 2016, respectively. No other customer accounted for more than 10% of revenue or accounts receivable in 2017 or as of December 31, 2016.

Revenue

Revenue Recognition and Net Product Sales

Total revenues are comprised of product sales of Carticel, Epicel, MACI, bone marrow and surgical kits. Revenue is recognized when persuasive evidence of an arrangement exists, the goods are shipped or delivered, depending on shipping terms, title and risk of loss pass to the customer and collectability is reasonably assured. Shipping and handling costs are included as a component of revenue.

On June 30, 2016, the Company reduced the scope of the agreement with its exclusive distributor by terminating their services with respect to a significant portion of its Carticel sales. Prior to June 30, 2016, the distributor purchased and took title to Carticel upon shipment of the product and assumed credit and collection risk. The distributor worked with the payers on behalf of patients and surgeons to ensure medical coverage and to obtain reimbursement for Carticel implantation procedures. The Company retained all responsibility for shipment of the product to the surgical suite. In addition, revenue for Carticel was recorded net of a provision for rebates and cash discounts. These rebates and cash discounts were established by the Company at the time of sale, based on historical experience adjusted to reflect known changes in the factors that impact such reserves. For instance, the distributor of Carticel was entitled to chargeback incentives for services that are provided for based on the selling price to the end customer, under specific contractual arrangements. Cash discounts could also be granted for prompt payment.

Effective as of July 1, 2016, the Company transitioned to a direct sales model whereby the Company retains credit and collection risk from the end customer. The Company currently utilizes Dohmen Life Science Services, LLC (DLSS) to provide patient support services and reimbursement services, but this provider does not purchase and take title to Carticel or MACI.

The Company - also utilizes Vital Care, Inc. to provide data reporting services and to purchase, bill and collect from certain payers for Carticel and MACI.

The Company recognizes product revenues from sales of Carticel and MACI upon delivery to patients as long as (i) there is persuasive evidence that an arrangement exists between ourselves and the customer, (ii) collectability is reasonably assured and (iii) the price is fixed or determinable. Prior authorization or confirmation of coverage level by the patient’s private insurance plan, hospital or government payer is a prerequisite to the shipment of product to a patient. The Company's net product revenues are calculated by estimating expected payments for insurance, hospital or patient payments at the time it recognizes the gross revenue. The estimates are updated prospectively as new information becomes available.

In April 2017, the Company received notification from one of our services providers, Vital Care, Inc., of a contractual dispute between Vital Care, Inc. and the third-party payer related to certain of its insurance reimbursement claims associated with Carticel and MACI surgeries performed in 2016 and the first quarter of 2017. Vital Care, Inc. is attempting to resolve this matter with the payer, which may include appealing or resubmitting the claims. While the Company believes reimbursement will be obtained, the ultimate amount of reimbursement may be lower than initially estimated. During the three months ended March 31, 2017, the Company recorded a change in estimate for revenue reserves of $2.1 million related to 2016 sales and $0.7 million related to 2017 sales to reflect the lower reimbursement that would be obtained if the claims are ultimately required to be treated as out-of-network. In addition, the contractual dispute could impact amounts previously collected and certain amounts may need to be repaid while the matter is being resolved; therefore our liquidity may be negatively impacted. As a result of the continuing evaluation and assessment of these expected payments, our estimates for expected payments could change.

Concentration of Credit Risk

Revenue from one customer, the distributor in the U.S., represented approximately 63% of total revenue during the three months ended March 31, 2016. The next largest customer represented 16% and 13% total revenue during the three months ended March 31, 2017 and 2016, respectively. No other customer accounted for more than 10% of revenue or accounts receivable in 2017 or as of December 31, 2016.