Debt	12 Months Ended
Dec. 31, 2016
Debt Disclosure [Abstract]
Debt	Debt On March 8, 2016, the Company entered into a $15.0 million debt financing with Silicon Valley Bank (SVB) which on September 9, 2016, was replaced by an expanded term loan and revolving line of credit agreement with SVB and MidCap Financial Services, or MidCap, which together provide access to up to $20.0 million. The updated debt financing consists of a $4.0 million term loan which was drawn at the closing, a $4.0 million term loan which was drawn upon in November 2016, a $2.0 million term loan which became available upon the FDA's approval of the MACI BLA and which must be drawn by April 12, 2017, and up to $10.0 million of a revolving line of credit. The term loans are interest only (indexed to Wall Street Journal (WSJ) Prime plus 5.00%) until September 1, 2017 followed by 36 equal monthly payments of principal plus interest maturing September 9, 2020. The revolving credit is limited to a borrowing base calculated using eligible accounts receivable and maturing September 9, 2020 with an interest rate indexed to WSJ Prime plus 1.25%. The Company is subject to various financial and nonfinancial covenants including but not limited to a monthly minimum net revenue covenant (determined in accordance with GAAP), measured on a trailing twelve month basis. This covenant was renegotiated with SVB in December 2016 and the December 31, 2016 minimum revenue covenant was changed from $56 million to $52 million. In addition, the December 31, 2017 minimum revenue covenant is set at $60 million. SVB and MidCap have the ability to call debt based on material adverse change clauses which are subjectively determinable and result in a subjective acceleration clause. SVB and MidCap have a shared first priority perfected security interest in all assets of the Company other than intellectual property. As of December 31, 2016, there was an outstanding balance of $8.0 million under the term loan and $2.5 million under the revolving line of credit. The weighted average interest rate on the outstanding term and revolving credit loans as of December 31, 2016 was 7.7%. The remaining capacity under the revolving line of credit as of December 31, 2016 was $7.5 million and we were, and continue to be, in compliance with our financial and non-financial debt covenants. The net revenue financial covenant was updated in an amendment to the credit agreement with SVB and MidCap in December 2016 In addition, warrants were issued in conjunction with the debt agreement as discussed in note 12. In determining whether the debt replacement is to be accounted for as a debt extinguishment or a debt modification, the Company considered whether creditors remained the same or changed and whether the changes in debt terms are substantial. After performing the assessment in accordance with accounting guidance for the modification of debt arrangements, this transaction was determined to be accounted for as a debt modification. As a result, the unamortized deferred financing costs now include $0.1 million from the original issue costs and lender fees and $0.3 million, in new issue costs, lender fees and warrant issuance costs which will be deferred over the life of the new debt arrangement.

Debt

On March 8, 2016, the Company entered into a $15.0 million debt financing with Silicon Valley Bank (SVB) which on September 9, 2016, was replaced by an expanded term loan and revolving line of credit agreement with SVB and MidCap Financial Services, or MidCap, which together provide access to up to $20.0 million. The updated debt financing consists of a $4.0 million term loan which was drawn at the closing, a $4.0 million term loan which was drawn upon in November 2016, a $2.0 million term loan which became available upon the FDA's approval of the MACI BLA and which must be drawn by April 12, 2017, and up to $10.0 million of a revolving line of credit. The term loans are interest only (indexed to Wall Street Journal (WSJ) Prime plus 5.00%) until September 1, 2017 followed by 36 equal monthly payments of principal plus interest maturing September 9, 2020. The revolving credit is limited to a borrowing base calculated using eligible accounts receivable and maturing September 9, 2020 with an interest rate indexed to WSJ Prime plus 1.25%. The Company is subject to various financial and nonfinancial covenants including but not limited to a monthly minimum net revenue covenant (determined in accordance with GAAP), measured on a trailing twelve month basis. This covenant was renegotiated with SVB in December 2016 and the December 31, 2016 minimum revenue covenant was changed from $56 million to $52 million. In addition, the December 31, 2017 minimum revenue covenant is set at $60 million. SVB and MidCap have the ability to call debt based on material adverse change clauses which are subjectively determinable and result in a subjective acceleration clause. SVB and MidCap have a shared first priority perfected security interest in all assets of the Company other than intellectual property. As of December 31, 2016, there was an outstanding balance of $8.0 million under the term loan and $2.5 million under the revolving line of credit. The weighted average interest rate on the outstanding term and revolving credit loans as of December 31, 2016 was 7.7%. The remaining capacity under the revolving line of credit as of December 31, 2016 was $7.5 million and we were, and continue to be, in compliance with our financial and non-financial debt covenants. The net revenue financial covenant was updated in an amendment to the credit agreement with SVB and MidCap in December 2016 In addition, warrants were issued in conjunction with the debt agreement as discussed in note 12.

In determining whether the debt replacement is to be accounted for as a debt extinguishment or a debt modification, the Company considered whether creditors remained the same or changed and whether the changes in debt terms are substantial. After performing the assessment in accordance with accounting guidance for the modification of debt arrangements, this transaction was determined to be accounted for as a debt modification. As a result, the unamortized deferred financing costs now include $0.1 million from the original issue costs and lender fees and $0.3 million, in new issue costs, lender fees and warrant issuance costs which will be deferred over the life of the new debt arrangement.