In December 2019, the Company issued $450.0 million aggregate principal amount of 0.125% convertible senior notes due 2024, including $75.0 million aggregate principal amount of 2024 Notes issued upon the initial purchasers’ exercise in full of their option to purchase additional 2024 Notes. The 2024 Notes will mature on December 15, 2024, unless earlier redeemed or repurchased by the Company or converted by the holder pursuant to their terms. Interest is payable semiannually in arrears on June 15 and December 15 of each year, commencing on June 15, 2020.

The 2024 Notes are governed by an Indenture between the Company, as issuer, and U.S. Bank National Association, as trustee (the “2024 Notes Indenture”). The 2024 Notes are unsecured and rank: senior in right of payment to the Company’s indebtedness that is expressly subordinated in right of payment to the 2024 Notes; equal in right of payment to the Company’s existing and future indebtedness that is not so subordinated, including its 1.50% convertible senior notes due 2022 (see 1.50% Convertible Senior Notes Due 2022 below); effectively junior in right of payment to any of the Company’s secured indebtedness to the extent of the value of the assets securing such indebtedness; and structurally junior to all existing and future indebtedness and other liabilities incurred by the Company’s subsidiaries.

Upon conversion, the Company will pay or deliver, as the case may be, cash, shares of the Company’s common stock or a combination of cash and shares of common stock, at the Company’s election.

The 2024 Notes have an initial conversion rate of 8.8999 shares of common stock per $1,000 principal amount of 2024 Notes. This represents an initial effective conversion price of approximately $112.36 per share of common stock and approximately 4.0 million shares issuable upon conversion. Throughout the term of the 2024 Notes, the conversion rate may be adjusted upon the occurrence of certain events. Holders of the 2024 Notes will not receive any cash payment representing accrued and unpaid interest, if any, upon conversion of a 2024 Note, except in limited circumstances. Accrued but unpaid interest will be deemed to be paid by cash, shares of the Company’s common stock or a combination of cash and shares of the Company’s common stock paid or delivered, as the case may be, to the holder upon conversion of a 2024 Note.

Holders may convert all or a portion of their 2024 Notes prior to the close of business on the business day immediately preceding June 15, 2024, in multiples of $1,000 principal amount, only under the following circumstances:

On or after June 15, 2024 until the close of business on the second scheduled trading day immediately preceding the maturity date, holders may convert all or any portion of their 2024 Notes at the conversion rate at any time regardless of whether the conditions set forth below have been met.

As of September 30, 2020, the 2024 Notes are not yet convertible. The 2024 Notes are classified as long-term on the condensed consolidated balance sheet as of September 30, 2020 as it is the Company’s intent to settle all of the debt at maturity or to settle in shares if exercised by the debt holder prior to maturity.

The 2024 Notes are not redeemable by the Company prior to December 20, 2022. The Company may redeem for cash all or any portion of the 2024 Notes, at its option, on or after December 20, 2022 if the last reported sale price of the Company's common stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive), including the trading day immediately preceding the date on which the Company provides notice of redemption, during any 30 consecutive trading day period ending on, and including, the trading day immediately preceding the date on which the Company provides notice of redemption at a redemption price equal to 100% of the principal amount of the 2024 Notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date.

Based on market data available for publicly traded, senior, unsecured corporate bonds issued by companies in the same industry and with similar maturity, the Company estimated the implied interest rate of its 2024 Notes to be approximately 5.16%, assuming no conversion option. Assumptions used in the estimate represent what market participants would use in pricing the equity component, including market interest rates, credit standing, and yield curves, all of which are defined as Level 2 observable inputs. The estimated implied interest rate was applied to the 2024 Notes, which resulted in a fair value of the liability component of $360.4 million upon issuance, calculated as the present value of implied future payments based on the $450.0 million aggregate principal amount. The excess of the principal amount of the liability component over its carrying amount, or the debt discount, is amortized to interest expense over the term of the 2024 Notes. The $89.6 million difference between the aggregate principal amount of $450.0 million and the estimated fair value of the liability component was recorded in additional paid-in capital as the 2024 Notes were not considered redeemable.

Significant judgment is required in determining the liability component of the related convertible senior notes as well as the balance sheet classification of the elements of the convertible senior notes. The Company accounted for the convertible senior notes and the partial extinguishment of the 2022 Notes, discussed below, as separate liability and equity components, determining the fair value of the respective liability components based on an estimate of the fair value of a similar liability without a conversion option and assigning the residual value to the equity component.

The Company estimated the fair value of the liability component of the convertible senior notes using a discounted cash flow model with a risk adjusted yield for similar debt instruments, absent any embedded conversion feature. In estimating the risk adjusted yield, the Company utilized both an income and market approach. For the income approach, the Company used a convertible bond pricing model, which included several assumptions including volatility and the risk-free rate. For the market approach, the Company performed an evaluation of issuances of convertible debt securities issued by other comparable companies. Additionally, a detailed analysis of the terms of the convertible senior notes transactions was required to determine existence of any derivatives that may require separate mark-to-market accounting under applicable accounting guidance.

In accounting for the transaction costs related to the issuance of the 2024 Notes, the Company allocated the total amount incurred to the liability and equity components based on their estimated relative fair values. Transaction costs attributable to the liability component, totaling $10.2 million, are being amortized to expense over the term of the 2024 Notes, and transaction costs attributable to the equity component, totaling $2.6 million, and were netted with the equity component in shareholders’ equity.

	As of			As of
	September 30, 2020			December 31, 2019
Liability component:
Principal	$	450,000		$	450,000
Less: debt discount, net of amortization		(85,549	)		(98,942	)
Net carrying amount	$	364,451		$	351,058
Equity component ⁽¹⁾		86,133			86,133

The following table sets forth total interest expense recognized related to the 2024 Notes (in thousands):

	Three Months Ended September 30, 2020		Nine Months Ended September 30, 2020
0.125% coupon	$	141	$	422
Amortization of debt discount and transaction costs		4,521		13,393
	$	4,662	$	13,815

As of September 30, 2020 and December 31, 2019, the fair value of the 2024 Notes, which was determined based on inputs that are observable in the market or that could be derived from, or corroborated with, observable market data, quoted price of the 2024 Notes in an over-the-counter market (Level 2), and carrying value of debt instruments (carrying value excludes the equity component of the Company’s 2024 Notes classified in equity) were as follows (in thousands):

	As of September 30, 2020				As of December 31, 2019
	Fair Value		Carrying Value		Fair Value		Carrying Value
2024 Notes	$	596,709	$	364,451	$	450,414	$	351,058

In connection with the issuance of the 2024 Notes, the Company entered into capped call transactions with certain counterparties affiliated with the initial purchasers and other financial institutions. The capped call transactions are expected to reduce potential dilution of earnings per share upon conversion of the 2024 Notes. Under the capped call transactions, the Company purchased capped call options that in the aggregate relate to the total number of shares of the Company’s common stock underlying the 2024 Notes, with an initial strike price of approximately $112.36 per share, which corresponds to the initial conversion price of the 2024 Notes and is subject to anti-dilution adjustments substantially similar to those applicable to the conversion rate of the 2024 Notes, and with a cap price of approximately $166.46. The cost of the purchased capped calls of $44.9 million was recorded to shareholders’ equity and will not be re-measured.

Based on the closing price of the Company’s common stock of $125.73 on September 30, 2020, the if-converted value of the 2024 Notes was more than their respective principal amounts.

In November 2017, the Company issued $115.0 million aggregate principal amount of 1.50% convertible senior notes due 2022 including $15.0 million aggregate principal amount of 2022 Notes issued upon the initial purchasers’ exercise in full of their option to purchase additional 2022 Notes. The 2022 Notes will mature on November 1, 2022, unless earlier redeemed or repurchased by the Company or converted by the holder pursuant to their terms. Interest is payable semiannually in arrears on May 1 and November 1 of each year, commencing on May 1, 2018.

The 2022 Notes are governed by an Indenture between the Company, as issuer, and U.S. Bank, National Association, as trustee (the “2022 Notes Indenture”). The 2022 Notes are unsecured and rank: senior in right of payment to the Company’s future indebtedness that is expressly subordinated in right of payment to the 2022 Notes; equal in right of payment to the Company’s existing and future indebtedness that is not so subordinated, including the Company’s 2024 Notes; effectively subordinated in right of payment to any of the Company’s secured indebtedness to the extent of the value of the assets securing such indebtedness; and structurally subordinated to all existing and future indebtedness and other liabilities incurred by the Company’s subsidiaries.

Upon conversion, the Company will pay or deliver, as the case may be, cash, shares of the Company’s common stock or a combination of cash and shares of common stock, at the Company’s election. The Company’s current intention is to settle the conversion in shares of common stock if a conversion were to occur.

The 2022 Notes have an initial conversion rate of 29.6626 shares of common stock per $1,000 principal amount of 2022 Notes. This represents an initial effective conversion price of approximately $33.71 per share of common stock and initially approximately 3.4 million shares issuable upon conversion. Throughout the term of the 2022 Notes, the conversion rate may be adjusted upon the occurrence of certain events. Holders of the 2022 Notes will not receive any cash payment representing accrued and unpaid interest, if any, upon conversion of a 2022 Note, except in limited circumstances. Accrued but unpaid interest will be deemed to be paid by cash, shares of the Company’s common stock or a combination of cash and shares of the Company’s common stock paid or delivered, as the case may be, to the holder upon conversion of a 2022 Note.

Holders may convert all or a portion of their 2022 Notes prior to the close of business on the business day immediately preceding May 1, 2022, in multiples of $1,000 principal amount, only under the following circumstances:

On or after May 1, 2022, until the close of business on the second scheduled trading day immediately preceding the maturity date, holders may convert all or any portion of their 2022 Notes at the conversion rate at any time regardless of whether the conditions set forth below have been met.

The 2022 Notes are not redeemable by the Company prior to November 6, 2020. The Company may redeem for cash all or any portion of the 2022 Notes, at its option, on or after November 6, 2020 if the last reported sale price of the Company's common stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive), including the trading day immediately preceding the date on which the Company provides notice of redemption, during any 30 consecutive trading day period ending on, and including, the trading day immediately preceding the date on which the Company provides notice of redemption at a redemption price equal to 100% of the principal amount of the 2022 Notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date. The Company has not provided notice to exercise its option to redeem the 2022 Notes.

Based on the market price of the Company’s common stock during the 30 trading days preceding June 30, 2018, the 2022 Notes were convertible at the option of the debt holder as of September 30, 2018 and continue to be convertible at the option of the debt holder as of September 30, 2020.

In connection with the issuance of the 2024 Notes in December 2019, the Company paid $57.8 million to repurchase $23.0 million aggregate principal amount of the 2022 Notes. The Company determined the fair value of the liability portion being extinguished immediately prior to extinguishment. Based on market data available for publicly traded, senior, unsecured corporate bonds issued by companies in the same industry and with similar maturity, the Company estimated the implied interest rate of its 2022 Notes to be approximately 4.64%. The fair value of such liability portion was then deducted from the amount of consideration transferred and allocated to the liability component. The difference between the fair value of the liability and its carrying value, inclusive of any unamortized debt issue costs, were recognized as an extinguishment loss in the amount of $1.4 million in Loss on extinguishment of

convertible notes on the consolidated statement of operations and comprehensive loss during the year ended December 31, 2019. The remaining consideration was allocated to the reacquisition of the equity component and recognized as a reduction of Additional paid-in capital on the consolidated balance sheet in the amount of $36.7 million. The Company also partially terminated capped call options entered into in connection with the 2022 Notes during fiscal year 2019 and received $5.8 million recorded to additional paid-in capital on the consolidated balance sheet.

During the three months ended September 30, 2020, the Company issued 29,898 shares upon the conversion of approximately $1.0 million in aggregate principal amount of the 2022 Notes and recognized $0.9 million in additional paid-in capital on the condensed consolidated balance sheet related to shares issued. The Company determined the fair value of the liability portion being extinguished immediately prior to extinguishment. Based on market data available for publicly traded, senior, unsecured corporate bonds issued by companies in the same industry and with similar maturity, the Company estimated the implied interest rate of its 2022 Notes to be approximately 4.64%. The fair value of such liability portion was then deducted from the amount of consideration transferred and allocated to the liability component. The difference between the fair value of the liability and its carrying value, inclusive of any unamortized debt issue costs, was recognized as an extinguishment loss. The Company recognized an immaterial amount of extinguishment loss during the three months ended September 30, 2020.

The 2022 Notes are classified as long-term on the consolidated balance sheet as of September 30, 2020 and December 31, 2019. The Company may repurchase the 2022 Notes prior to maturity and intends to settle in shares if exercised by the debt holder prior to maturity.

Based on market data available for publicly traded, senior, unsecured corporate bonds issued by companies in the same industry and with similar maturity, the Company estimated the implied interest rate of its 2022 Notes at the time of issuance to be approximately 6.93%, assuming no conversion option. Assumptions used in the estimate represent what market participants would use in pricing the equity component, including market interest rates, credit standing, and yield curves, all of which are defined as Level 2 observable inputs. The estimated implied interest rate was applied to the 2022 Notes, which resulted in a fair value of the liability component of $92.1 million upon issuance, calculated as the present value of implied future payments based on the $115.0 million aggregate principal amount. The excess of the principal amount of the liability component over its carrying amount, or the debt discount, is amortized to interest expense over the term of the 2022 Notes. The $22.9 million difference between the aggregate principal amount of $115.0 million and the estimated fair value of the liability component was recorded in additional paid-in capital as the 2022 Notes were not considered redeemable.

In accounting for the transaction costs related to the issuance of the 2022 Notes, the Company allocated the total amount incurred to the liability and equity components based on their estimated relative fair values. Transaction costs attributable to the liability component on the remaining outstanding notes as of the issuance date, totaling $2.5 million, are being amortized to expense over the term of the 2022 Notes, and transaction costs attributable to the equity component as of the issuance date, totaling $0.8 million, and were netted with the equity component in shareholders’ equity.

	As of			As of
	September 30, 2020			December 31, 2019
Liability component:
Principal	$	90,992		$	92,000
Less: debt discount, net of amortization		(9,528	)		(12,776	)
Net carrying amount	$	81,464		$	79,224
Equity component ⁽¹⁾		(19,167	)		(14,555	)

The following table sets forth total interest expense recognized related to the 2022 Notes (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019
1.50% coupon	$	342	$	429	$	1,032	$	1,294
Amortization of debt discount and transaction costs		1,057		1,243		3,134		3,667
	$	1,399	$	1,672	$	4,166	$	4,961

As of September 30, 2020 and December 31, 2019, the fair value of the 2022 Notes, which was determined based on inputs that are observable in the market or that could be derived from, or corroborated with, observable market data, quoted price of the 2022 Notes in an over-the-counter market (Level 2), and carrying value of debt instruments (carrying value excludes the equity component of the Company’s convertible notes classified in equity) were as follows (in thousands):

	As of September 30, 2020				As of December 31, 2019
	Fair Value		Carrying Value		Fair Value		Carrying Value
2022 Notes	$	363,974	$	81,464	$	215,801	$	79,224

In connection with the issuance of the 2022 Notes, the Company entered into capped call transactions with certain counterparties affiliated with the initial purchasers and others. The capped call transactions are expected to reduce potential dilution of earnings per share upon conversion of the 2022 Notes. Under the capped call transactions, the Company purchased capped call options that in the aggregate relate to the total number of shares of the Company’s common stock underlying the 2022 Notes, with an initial strike price of approximately $33.71 per share, which corresponds to the initial conversion price of the 2022 Notes and is subject to anti-dilution adjustments substantially similar to those applicable to the conversion rate of the 2022 Notes, and have a cap price of approximately $47.20. The cost of the purchased capped calls of $12.9 million was recorded to shareholders’ equity and will not be re-measured.

Based on the closing price of the Company’s common stock of $125.73 on September 30, 2020, the if-converted value of the 2022 Notes was more than their respective principal amounts.