On November 14, 2017, the Company issued $570.0 million senior notes due on November 15, 2024 (the “2024 Notes”). The 2024 Notes were issued at face value and bear interest at the rate of 1.50% per annum, payable semi-annually in cash on each May 15 and November 15, commencing on May 15, 2018.

Upon conversion, the Company may pay cash, shares of its common stock or a combination of cash and stock, as determined by the Company in its discretion. The 2024 Notes may be convertible into 7,763,552 shares of the Company’s common stock under certain circumstances prior to maturity at a conversion rate of 13.621 shares per $1,000 principal amount of the 2024 Notes, which represents a conversion price of $73.42 per share, subject to adjustment under certain conditions.

The Company allocated the proceeds received from issuance of the 2024 Notes between the liability component and the embedded conversion option, or equity component. The liability component was determined by measuring the fair value of similar notes that do not include the embedded conversion option. The Company allocated $161.1 million to the equity component, which was determined by deducting the fair value of the liability component from the par value of the 2024 Notes. The equity component, net of allocated offering costs of $4.2 million, was recorded as an increase additional paid-in capital. The equity component, plus $10.6 million of offering costs allocated to the liability component, represent the total debt discount on the 2024 Notes at issuance. The debt discount will be amortized under an effective interest method and recorded as additional interest expense over the life of the 2024 Notes. The effective interest rate on the liability component of the 2024 Notes for the year ended December 31, 2018 and 2017 was 6.9%.

Upon the occurrence of a “fundamental change”, which includes (1) change in beneficial ownership of the Company where any person/group possesses more than 50% of the voting power of the Company, (2) consolidation or merger of the Company, (3) shareholder approval of a liquidation plan or (4) the Company is delisted from NYSE or NASDAQ, the holders may require the Company to repurchase all or a portion of the 2024 Notes for cash at 100% of the principal amount of the 2024 Notes being purchased, plus any accrued and unpaid interest. Additionally, upon the occurrence of a “make-whole fundamental change” prior to the maturity date, the Company shall adjust the conversion rate on a sliding scale basis detailed in the agreement

To minimize the impact of potential dilution upon conversion of the 2024 Notes, the Company separately entered into capped call transactions with certain counterparties. The capped calls have a strike price of $73.42 and a cap price of $104.88 and are exercisable when and if the 2024 Notes are converted. If, upon conversion of the 2024 Notes, the price of the Company’s common stock is between the strike price and the cap price of the capped calls, the counterparties will deliver shares of the Company’s common stock and/or cash with an aggregate value equal to the difference between the price of the Company’s common stock at the conversion date and the strike price, multiplied by the number of shares of the Company’s common stock related to the capped calls being exercised. The Company paid $50.9 million for these capped calls transactions, which was recorded as additional paid-in capital.

In July 2017, the Company entered into an amended and restated credit agreement (the “Amended and Restated Credit and Security Agreement”) which provides a term loan (“July 2017 Term Loan”) of $60.0 million with MidCap Financial Trust (“MidCap”). Borrowings under the Amended and Restated Credit and Security Agreement bore interest at a rate per annum equal to 6.25%, plus the one-month London Interbank Offered Rate (“LIBOR”). In addition to paying interest on the outstanding principal under the Amended and Restated Credit and Security Agreement, the Company paid an origination fee equal to 0.50% of the amount of the term loan when advanced under the Amended and Restated Credit and Security Agreement and would be liable for a final payment fee equal to 2.00% of the amount borrowed under the Amended and Restated Credit and Security Agreement when the July 2017 Term Loan was fully repaid. Commencing on July 1, 2018, and continuing for the remaining thirty six months of the facility, the Company was required to make monthly principal payments of approximately $0.8 million, set forth in the Amended and Restated Credit and Security Agreement, subject to certain adjustments as described therein. The facility would mature in July 2021.

In July 2017, the Company also entered into a revolving credit and security agreement (the “Revolving Credit Agreement”) which provides an aggregate revolving loan commitment of $40.0 million (which may be increased by an additional tranche of $20.0 million) with MidCap. Borrowings under the Revolving Credit Agreement bore interest at a rate of 3.95%, plus the one-month LIBOR. In addition to paying interest on the outstanding principal under the Revolving Credit Agreement, the Company paid $0.2 million of origination fees, which was 0.50% of the amount of the revolving loan. The Company recognized this origination fee as other asset and it was amortized to interest expense over the term of the revolving loan.

In September 2018, the Company terminated both the Amended and Restated Credit and Security Agreement and the Revolving Credit Agreement with MidCap and paid off the remaining outstanding balance of principal and accrued and unpaid interest on the July 2017 Term Loan. As a result, the Company recorded a debt extinguishment loss of $2.3 million primarily related to the write-off of unamortized debt issuance costs and prepayment fees.

The Company had two mortgage loans outstanding which bear interest at 4.75% with the original maturity date of February 2027 and were collateralized by a facility in Corvallis, Oregon. At December 31, 2017, these loans had unpaid principal balances of $0.8 million and $0.5 million, for a total indebtedness of $1.3 million, and were presented as current portion of long-term debt on the consolidated balance sheet. In connection with the sale of this property in January 2018, the two long-term mortgage loans were paid off.

As of December 31, 2018, the Company recorded approximately $420.6 million as long-term debt on the consolidated balance sheets. For the years ended December 31, 2018, 2017 and 2016, the Company recorded $33.7 million, $5.8 million and $1.9 million of interest expense, respectively.

The following table summarizes the Company’s debt facilities for the periods indicated:

	As of December 31, 2018			As of December 31, 2017
	(in thousand)			(in thousand)
Par value of the 2024 Notes	$	570,000		$	570,000
Unamortized discount - equity component		(140,206	)		(158,890	)
Unamortized discount - debt issuance costs		(9,240	)		(10,449	)
Net carrying value of convertible debt		420,554			400,661
Net carrying value of other debt facilities		—			30,390
Net carrying value of total debt facilities		420,554			431,051

Fair value of convertible debt	$	952,681		$	619,641

The fair value of the Company’s 2024 Notes is based on open market trades and is classified as level 1 in the fair value hierarchy.

The following table summarizes the total gross payments due under the Company’s debt arrangements:

	As of December 31, 2018
	(in thousands)
2019	$	—
2020		—
2021		—
2022		—
2023		—
Thereafter		570,000
Total Payments	$	570,000