Long-term debt

As of June 30, 2018 and December 31, 2017, long-term debt consisted of the following (in thousands):



	June 30, 2018			December 31, 2017
Term Loans
Term Loan A - $10.0 million at 6.9% interest	$	7,619		$	7,619
Term Loan B - $10.0 million at 6.9% interest	7,619			7,619
Term Loan C - $15.0 million at 7.4% interest	12,000			12,000
Final fee obligation	2,429			2,429
Unamortized issuance costs	(1,079		)	(1,641		)
Total debt, net	28,588			28,026
Current portion of long-term debt	(19,009		)	(7,927		)
Long-term debt	$	9,579		$	20,099

Term Loans

In January 2015, the Company entered into a Loan and Security Agreement, or the LSA, with Solar Capital Partners (as successor-in-interest to General Electric Capital Corporation), and certain other financial institutions party thereto, as lenders, pursuant to which the Company obtained (a) up to $35,000,000 in a series of term loans and (b) a revolving loan in the maximum amount of $5,000,000. As of June 30, 2018, the Company had borrowed all $35,000,000 under the term loans as provided in the LSA. As of June 30, 2018, the Company had not borrowed any of the $5,000,000 available under the revolving loan.

The term loans will accrue interest at a rate equal to (a) the greater of 1.00% or the three year treasury rate in effect at the time of funding, plus (b) an applicable margin between 4.95% and 5.90% per annum. The Company is only required to make interest payments on amounts borrowed pursuant to the term loans from the applicable funding date until January 1, 2019, or the Interest Only Period. Following the Interest Only Period, monthly installments of principal and interest under the Term Loans will be due until the original principal amount and applicable interest is fully repaid by March 12, 2020.

Under the LSA, the Company is required to comply with certain affirmative and negative covenants, including, without limitation, delivering reports and notices relating to the Company’s financial condition and certain regulatory events and intellectual property matters, as well as limiting the creation of liens, the incurrence of indebtedness, and the making of certain investments, dividends, payments and acquisitions, other than as specifically permitted by the LSA. As of June 30, 2018, the Company was in compliance with all covenants under the LSA.

Revolving Loan

Pursuant to the LSA, the Company may borrow up to $5,000,000 under a revolving loan facility. Borrowings under the revolving loan will accrue interest at a rate equal to (a) the greater of 1.25% per annum or a base rate as determined by a three-month LIBOR-based formula, plus (b) an applicable margin between 2.95% and 3.95% based on certain criteria as set forth in the LSA. All principal and interest outstanding under the revolving loan is due and payable on the Maturity Date. The Company is required to pay a commitment fee equal to 0.75% per annum of the amounts made available but unborrowed under the revolving loan. As of June 30, 2018, the Company had not borrowed any amounts pursuant the revolving loan facility.

Debt Issuance Costs

As of June 30, 2018 and December 31, 2017, the Company had $1,079,000 and $1,641,000, respectively, of unamortized debt issuance discount, which is offset against borrowings in long-term and short-term debt.

Amortization of debt issuance costs was $293,000 and $342,000 for the three months ended June 30, 2018 and 2017, respectively, and was $583,000 and $493,000 for the six months ended June 30, 2018 and 2017, respectively. Amortization of debt issuance costs is included in interest expense in the Company's unaudited condensed consolidated statements of comprehensive loss for the periods presented.

Letter of Credit

In September 2012, the Company provided a $758,000 letter of credit issued by Banc of California to the landlord of its executive office facility in Carlsbad, California. This letter of credit was secured with $758,000 of restricted cash as of June 30, 2018.