The carrying value of the Company's convertible senior notes is as follows:



	March 31, 2024			December 31, 2023
	(Amounts in thousands, except percentage data)
1.00% Convertible Senior Notes due 2028:
Principal amount	$	600,000		$	600,000
Unamortized debt discount	$	(78,132	)	$	(81,457	)
Unamortized debt issuance costs		(7,950	)		(8,400	)
Carrying amount - Convertible Senior Notes due 2028, net	$	513,918		$	510,143
0.375% Convertible Senior Notes due 2024:
Principal amount	$	69,616		$	69,700
Unamortized debt issuance costs		(136	)		(248	)
Carrying amount - Convertible Senior Notes due 2024, net	$	69,480		$	69,452

On December 14, 2023, the Company issued $600.0 million aggregate principal amount of its 2023 Notes in the Exchange and Subscription Agreements with a limited number of holders of its outstanding 2019 Notes and certain other qualified institutional buyers pursuant to Rule 144A under the Securities Act. Pursuant to the Exchange and Subscription Agreements and to the Exchange Transaction, the Company issued $290.1 million aggregate principal amount of the 2023 Notes in a private placement to accredited institutional buyers (the “Subscription Transactions”) for $290.1 million in cash.

The Company evaluated the Exchange Transaction and determined approximately $29.6 million of the $217.7 million principal of the exchanged 2019 Notes should be accounted for as extinguishments of debt and approximately $188.1 million should be accounted for as modification of debt. As a result, we recognized a $12.7 million loss on extinguishment of debt in our consolidated statements of comprehensive income for the year ended December 31, 2023, inclusive of $0.1 million of unamortized debt issuance costs. Under modification accounting, the carrying amount of the modified 2019 Notes was reduced by $2.8 million, with a corresponding increase to additional paid-in capital, to account for the increase in the fair value of the embedded conversion option, representing a debt discount of the modified 2019 Notes. The aggregate debt discount of $78.1 million as of March 31, 2024, comprised of $75.5 million increase in principal of the modified 2019 Notes and a $2.6 million increase in the fair value of the embedded conversion option. The aggregate debt discount of $82.1 million as of December 31, 2023, comprised of $79.3 million increase in principal of the modified 2019 Notes and a $2.8 million increase in the fair value of the embedded conversion option. These amounts are presented as a direct reduction from the carrying value of the convertible debt in their respective periods presented in our condensed consolidated balance sheets. This amount is being accreted into interest expense in the condensed consolidated statements of comprehensive (loss) income using the effective interest method over the term of the 2023 Notes.

Proceeds from the Subscription Transactions were $276.1 million, net of debt issuance costs of $13.9 million. The Exchange Transaction resulted in $6.2 million of the debt issuance costs related to the modified 2019 Notes, which were expensed as incurred in accordance with modification accounting, and $7.7 million of deferred debt issuance costs related to the 2023 Notes, which were recorded as a direct deduction to the carrying value of the 2023 Notes on the Company’s condensed consolidated balance sheets. The Company is amortizing the $7.7 million of debt issuance costs of the 2023 Notes into amortization of debt issuance costs in the Company’s condensed consolidated statements of comprehensive (loss) income over the remaining term of the 2023 Notes. The carrying value of the 2023 Notes of $513.9 million and $510.1 million is included in long-term debt on the Company's condensed consolidated balance sheets as of March 31, 2024 and December 31, 2023, respectively.

The Company used $14.4 million of the proceeds from the Subscription Transactions to repurchase shares of its common stock from certain purchasers of the 2023 Notes. For more information regarding this repurchase, see Note 12, “Stockholders’ Equity - Share Repurchases” included in Part II, Item 8, “Financial Statements and Supplementary Data,” to the Company's Form 10-K. The Company will also use a portion of the proceeds to finance in part, the settlement upon conversion or repurchase of the remaining 2019 Notes at or prior to maturity. The remainder of the proceeds will be used for working capital.

The 2023 Notes are senior, unsecured obligations of the Company, and bear interest at a rate of 1.00% per year. Interest is payable semi-annually in arrears on each of June 15 and December 15, commencing on June 15, 2024. The 2023 Notes will mature on December 15, 2028, unless earlier redeemed, repurchased or converted. The initial conversion rate for the 2023 Notes is 4.9247 shares of the Company’s common stock per $1,000 principal amount of 2023 Notes, which is equivalent to an initial conversion price of $203.06 per share and represents a 30% premium over the last reported sale price of $156.20 per share on December 6, 2023, the date on which the 2023 Notes were priced. Prior to the close of business on the business day immediately preceding September 15, 2028, the 2023 Notes will be convertible at the option of the holders of 2023 Notes only upon the satisfaction of specified conditions and during certain quarters commencing after the calendar quarter ending on March 31, 2024, into cash up to their principal amount, and into cash, shares of the Company’s common stock or a combination thereof, at the Company’s election, for the conversion value above the principal amount, if any. Thereafter until the close of business on the second scheduled trading day immediately preceding the maturity date, the 2023 Notes will be convertible at the option of the holders of 2023 Notes at any time regardless of these conditions. The Company may redeem for cash, all or a portion of the 2023 Notes, at its option, on or after December 18, 2026 and prior to the 21st scheduled trading day immediately preceding the maturity date at a redemption price of 100% of the principal amount of the 2023 Notes to be redeemed, plus accrued and unpaid interest to, but excluding the redemption date, if certain conditions are met in accordance to the indenture governing the 2023 Notes (the “2023 Notes Indenture”). For more information on the 2023 Notes, see Note 14, “Convertible Senior Notes,” included in Part II, Item 8, “Financial Statements and Supplementary Data,” to the Company’s Form 10-K.

The following table sets forth total interest expense recognized related to the 2023 Notes for the three months ended March 31, 2024 for which there were no comparable amounts for the same period of 2023 (amounts in thousands, except percentage data):


	Three Months Ended March 31,
	2024
Contractual interest expense – 2023 Notes	$	1,500
Amortization of debt discount – 2023 Notes		3,326
Amortization of debt issuance costs – 2023 Notes		371
Total	$	5,197
Effective interest rate of the liability component		4.39	%

At March 31, 2024 and December 31, 2023, the carrying value of the 2023 Notes was $513.9 million and $510.1 million, respectively, net of unamortized discount, and the fair value of the 2023 Notes was $587.0 million and $596.0 million, respectively. The fair value of the 2023 Notes was determined based on the most recent trade activity of the 2023 Notes at March 31, 2024 and December 31, 2023.

The Company issued $287.5 million aggregate principal amount of the 2019 Notes on July 19, 2019 in a transaction which included the underwriters’ exercise in full of an option to purchase an additional $37.5 million aggregate principal amount of the 2019 Notes (the “Notes Offering”). The net proceeds of the Notes Offering, after deducting underwriting discounts and commissions and other related offering expenses payable by the Company, were approximately $278.5 million. Immediately following the closing of the Exchange Transaction mentioned above, $69.7 million in aggregate principal amount of the 2019 Notes remained outstanding as of December 31, 2023. As of March 31, 2024, subsequent to the conversion of another $0.1 million, $69.6 million in aggregate principal amount remains outstanding.

The 2019 Notes are senior, unsecured obligations of the Company, and bear interest at a rate of 0.375% per year. Interest is payable semi-annually in arrears on January 15 and July 15 of each year, beginning on January 15, 2020. The remaining 2019 Notes will mature on July 15, 2024, unless earlier repurchased or converted in accordance with their terms. The initial conversion rate for the 2019 Notes is 8.6749 shares of the Company’s common stock per $1,000 principal amount of 2019 Notes (which is equivalent to an initial conversion price of approximately $115.28 per share). Prior to the close of business on the business day immediately preceding April 15, 2024, the 2019 Notes will be convertible at the option of the holders of 2019 Notes only upon the satisfaction of specified conditions and during certain periods. Thereafter until the close of business on the second scheduled trading day immediately preceding the maturity date, the remaining 2019 Notes will be convertible at the options of the holders of 2019 Notes at any time regardless of these conditions. The 2019 Notes are not redeemable by the Company prior to maturity.

During the first quarter of 2024, the closing price of the Company’s common stock exceeded 130% of the conversion price of the 2019 Notes for more than 20 trading days of the last 30 consecutive trading days of the quarter. As a result, the 2019 Notes are convertible at the option of the holders of the 2019 Notes during the second quarter of 2024, the quarter immediately following the quarter when the conditions are met, as stated in the terms of the 2019 Notes. These conditions have been met each quarter since the third quarter of 2020. As a result, as of the date of this filing, excluding the Exchange Transaction mentioned above, the Company has received requests to convert $0.2 million aggregate principal amount of the 2019 Notes and all but $0.1 million have been settled as of March 31, 2024. The remaining outstanding requests for conversions will settle in the second quarter of 2024. The conversions resulted in the issuance of a nominal number of shares of the Company’s common stock to the note holders. Because the 2019 Notes mature within one year of the report date, the Company classifies the carrying value of the 2019 Notes as current liabilities on the Company’s condensed consolidated balance sheets at March 31, 2024.

The following table sets forth total interest expense recognized related to the 2019 Notes:


	Three Months Ended March 31,
	2024			2023
	(Amounts in thousands, except percentage data)
Contractual interest expense – 2019 Notes	$	65		$	270
Amortization of debt issuance costs – 2019 Notes		112			457
Total	$	177		$	727
Effective interest rate of the liability component		1.00	%		1.00	%

At March 31, 2024 and December 31, 2023, the carrying value of the 2019 Notes was $69.5 million, respectively, net of unamortized discount, and the fair value of the 2019 Notes was $119.0 million and $109.8 million, respectively. The fair value of the 2019 Notes was determined based on the most recent trade activity of the 2019 Notes at March 31, 2024 and December 31, 2023.