Prospectus supplement
(To prospectus dated June 4, 2019)
$200,000,000
0.250% Convertible Senior Notes due 2024
Interest payable June 1 and December 1
We are offering $200,000,000 principal amount of our
0.250% Convertible Senior Notes due 2024 (the notes). The notes will bear interest at a rate of 0.250% per year, payable semiannually in arrears on June 1 and December 1 of each year, beginning on December 1, 2019. The
notes will mature on June 1, 2024, unless earlier repurchased, redeemed or converted. This prospectus supplement and the accompanying prospectus also register the offering and sale of the shares of common stock issuable upon conversion of the
notes.
Holders may convert their notes at their option at any time prior to the close of business on the business day immediately preceding
December 1, 2023 only under the following circumstances: (1) during any calendar quarter commencing after the calendar quarter ending on September 30, 2019 (and only during such calendar quarter), if the last reported sale price of
our Class A common stock, par value $0.0001 per share (Class A common stock), for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading
day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day; (2) during the five business day period after any five consecutive trading day period (the
measurement period) in which the trading price (as defined in this prospectus supplement) per $1,000 principal amount of notes for each trading day of the measurement period was less than 98% of the product of the last reported sale
price of our Class A common stock and the conversion rate on each such trading day; (3) if we call any or all of the notes for redemption, at any time prior to the close of business on the scheduled trading day immediately preceding the
redemption date; or (4) upon the occurrence of specified corporate events. On or after December 1, 2023 until the close of business on the business day immediately preceding the maturity date, holders may convert their notes at any time,
regardless of the foregoing circumstances. Upon conversion, we will pay or deliver, as the case may be, cash, shares of our Class A common stock or a combination of cash and shares of our Class A common stock, at our election, as described
in this prospectus supplement.
The conversion rate will initially be 21.5049 shares of Class A common stock per $1,000 principal amount of notes
(equivalent to an initial conversion price of approximately $46.50 per share of Class A common stock). The conversion rate will be subject to adjustment in some events but will not be adjusted for any accrued and unpaid interest. In addition,
following certain corporate events that occur prior to the maturity date or if we deliver a notice of redemption, we will, in certain circumstances, increase the conversion rate for a holder who elects to convert its notes in connection with such a
corporate event or redemption, as the case may be.
We may not redeem the notes prior to June 6, 2022. We may redeem for cash all or any portion of
the notes, at our option, on or after June 6, 2022 if the last reported sale price of our Class A common stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive), during
any 30 consecutive trading day period (including the last trading day of such period) ending on, and including, the trading day immediately preceding the date on which we provide notice of redemption at a redemption price equal to 100% of the
principal amount of the notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date. No sinking fund is provided for the notes.
If we undergo a fundamental change, as defined in this prospectus supplement, holders may require us to repurchase for cash all or any portion of their notes at a fundamental change repurchase price equal to 100%
of the principal amount of the notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date.
The
notes will be our senior unsecured obligations and will rank senior in right of payment to any of our indebtedness that is expressly subordinated in right of payment to the notes; equal in right of payment to any of our unsecured indebtedness that
is not so subordinated; effectively junior in right of payment to any of our secured indebtedness to the extent of the value of the assets securing such indebtedness; and structurally junior to all indebtedness and other liabilities (including trade
payables) of our subsidiaries.
We do not intend to apply to list the notes on any securities exchange or any automated dealer quotation system. Our
Class A common stock is listed on the Nasdaq Global Select Market under the symbol ALTR. The last reported sale price of our Class A common stock on the Nasdaq Global Select Market on June 5, 2019 was $35.77 per share.
Investing in the notes involves a high degree of risk. See
Risk factors
beginning on page
S-10 of
this prospectus supplement and the documents incorporated by reference herein for a discussion of certain risks that you should consider in connection with an investment in the notes.
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Per note
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Total
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Public offering price(1)
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$
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1,000
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$
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200,000,000
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Underwriting discounts and commissions(2)
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$
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30
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$
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6,000,000
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Proceeds, before expenses, to us
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$
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970
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$
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194,000,000
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(1)
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Plus accrued interest, if any, from June 10, 2019
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(2)
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See Underwriting (conflicts of interest) beginning on page
S-77
of this prospectus supplement for additional information
regarding underwriting compensation.
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We have granted the underwriters the right to purchase, exercisable within a
30-day
period, up to an additional $30,000,000 principal amount of notes.
Neither the Securities and Exchange
Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal
offense.
We expect that delivery of the notes will be made to investors in book-entry form through The Depository Trust Company on or about
June 10, 2019.
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J.P. Morgan
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Goldman Sachs & Co. LLC
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RBC Capital Markets
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June 5, 2019