On March 5, 2018, we amended our senior credit facility to, among other things, extend the maturity date of the $25.0 million revolving credit facility, with a $5.0 million letter of credit sub-facility, to March 5, 2020, and provide for a new $20.0 million term loan. We incurred $9.0 million in term loan borrowings to refinance $7.9 million of term loan borrowings and $1.1 million of equipment loans and have $11.0 million of term loan borrowings available for general corporate purposes. The term loan amortizes over 36 months, beginning on April 1, 2019, following an initial interest-only period, and mature on March 1, 2022. We may prepay the term loan at any time, subject to a prepayment fee equal to 2.0% of the outstanding principal amount if prepaid on or before March 5, 2019, or 1.0% of the outstanding principal amount if prepaid after March 5, 2019, but on or before March 5, 2020.

On August 17, 2018, we amended our senior credit facility, to provide for a $4.0 million equipment advance which we used solely to purchase equipment. The equipment advance amortizes over 48 months, beginning September 1, 2018 and mature on August 1, 2022. We may prepay the equipment advance at any time, subject to a prepayment fee equal to 2% of the principal amount of the equipment advance if prepaid on or before August 17, 2019, or 1% of the principal amount of the equipment advance if prepaid after August 17, 2019, but on or before August 17, 2020.

The loans accrue interest, at our option, at (1) a LIBOR rate determined in accordance with the senior credit facility, plus a margin ranging from 2.75% to 4.00%, or (2) a prime rate determined in accordance with the senior credit facility, plus a margin ranging from 0.0% to 1.25%. The margin percentage is determined based upon whether the outstanding borrowing is a term loan, revolving loan, or an equipment advance and our adjusted EBITDA for the preceding 12-month period. Interest is due and payable in arrears monthly for prime rate loans and at the end of an interest period for LIBOR rate loans.

The senior credit facility includes financial and operating covenants, including a minimum liquidity ratio and maximum adjusted EBITDA loss threshold that both apply in the event we do not maintain a minimum liquidity threshold, which are set forth in detail in the credit facility agreement. We were in compliance with the covenants under our senior credit facility as of March 31, 2019. Our obligations under the senior credit facility are collateralized by substantially all our assets other than intellectual property.

At March 31, 2019, $20.0 million of term loan and $3.4 million equipment advance borrowings were outstanding, excluding unamortized debt issuance costs of $86,000, and no revolver borrowings were outstanding. Term loan and equipment advance interest rates were 6.25% and 6.75%, respectively. The following table presents the scheduled principal maturities as of March 31, 2019 (in thousands):

2019	$	5,750
2020		7,667
2021		7,667
2022		2,333
Total	$	23,417