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Convertible Senior Notes - Narrative (Details) |  |  |  | 1 Months Ended | 2 Months Ended | 3 Months Ended | 9 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Aug. 16, 2019 USD ($) | Aug. 15, 2019 USD ($) | May 22, 2018 USD ($) | Jun. 30, 2019 USD ($) | Nov. 30, 2018 shares | May 31, 2018 USD ($) d $ / shares shares | Aug. 31, 2014 USD ($) d $ / shares shares | Aug. 31, 2018 USD ($) | Apr. 30, 2018 USD ($) | Sep. 30, 2019 USD ($) shares | Sep. 30, 2018 USD ($) | Jun. 30, 2018 USD ($) | Sep. 30, 2019 USD ($) shares | Sep. 30, 2018 USD ($) | Dec. 31, 2018 USD ($) shares
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Conversion option fair value |  |  |  |  |  |  |  |  |  |  |  |  | $ 0 | $ 31,571,000 |
Derivative liability |  |  |  |  |  |  |  |  |  | $ 0 |  |  | 0 |  | $ 23,430,000
Derivative asset |  |  |  |  |  |  |  |  |  | $ 0 |  |  | $ 0 |  | $ 22,576,000
Warrants repurchased (shares) | shares |  |  |  |  | 525,000 |  |  |  |  |  |  |  |  |  |
Warrants outstanding (shares) | shares |  |  |  |  |  |  |  |  |  | 2,739,643 |  |  | 2,739,643 |  | 2,739,643
2023 Convertible Senior Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Warrant derivative in connection with Notes |  |  |  |  |  |  |  |  |  |  |  | $ 97,805,000 |  |  |
Convertible Notes | 2019 Convertible Senior Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount outstanding |  |  |  |  |  |  | $ 245,000,000.0 |  |  | $ 0 |  |  | $ 0 |  | $ 27,326,000
Effective interest rate (as a percent) |  |  |  |  |  |  | 5.83% |  |  |  |  |  |  |  |
Initial conversion rate (shares per $1,000) |  |  |  |  |  |  | 0.0133251 |  |  |  |  |  |  |  |
Initial conversion price (USD per share) | $ / shares |  |  |  |  |  |  | $ 75.05 |  |  |  |  |  |  |  |
Interest rate (as a percent) |  |  |  |  |  |  | 0.75% |  |  |  |  |  |  |  |
Conversion option fair value |  |  | $ 341,600,000 |  |  |  |  |  |  |  |  |  |  | 563,200,000 |
Increase (decrease) in if-converted value in excess of principal |  |  |  |  |  |  |  |  |  |  | $ 161,900,000 |  |  | $ 221,600,000 |
Notices for conversion |  |  |  | $ 1,000,000.0 |  |  |  | $ 195,900,000 | $ 21,800,000 |  |  |  |  |  |
Conversion value over the principal amount |  |  |  | $ 500,000 |  |  |  | $ 439,600,000 | 31,600,000 |  |  |  |  |  |
Gain (loss) on extinguishment of debt |  |  |  |  |  |  |  |  | $ (600,000) |  |  |  |  |  |
Repayments of notes | $ 0 | $ 26,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Debt premium | $ 0 | $ 11,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Gain (loss) on derivative |  |  |  |  |  |  |  |  |  |  |  |  | (10,200,000) |  |
Convertible Notes | 2019 Convertible Senior Notes | Debt Instrument, Redemption, Period One |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Threshold trading days | d |  |  |  |  |  |  | 20 |  |  |  |  |  |  |  |
Consecutive trading days | d |  |  |  |  |  |  | 30 |  |  |  |  |  |  |  |
Stock price trigger to classify convertible debt as current (as a percent) |  |  |  |  |  |  | 130.00% |  |  |  |  |  |  |  |
Convertible Notes | 2019 Convertible Senior Notes | Debt Instrument, Redemption, Period Two |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Threshold trading days | d |  |  |  |  |  |  | 5 |  |  |  |  |  |  |  |
Consecutive trading days | d |  |  |  |  |  |  | 10 |  |  |  |  |  |  |  |
Maximum threshold of debt trading price trigger (as a percent) |  |  |  |  |  |  | 98.00% |  |  |  |  |  |  |  |
Convertible Notes | 2023 Convertible Senior Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount outstanding |  |  |  |  |  | $ 750,000,000.0 |  |  |  | 750,000,000 |  |  | 750,000,000 |  | $ 750,000,000
Initial conversion rate (shares per $1,000) |  |  |  |  |  | 0.0040244 |  |  |  |  |  |  |  |  |
Initial conversion price (USD per share) | $ / shares |  |  |  |  |  | $ 248.48 |  |  |  |  |  |  |  |  |
Interest rate (as a percent) |  |  |  |  |  | 0.75% |  |  |  |  |  |  |  |  |
Debt premium |  |  |  |  |  | $ 13,700,000 |  |  |  |  |  |  |  |  |
Warrants issued in public offering (shares) | shares |  |  |  |  |  | 3,018,327 |  |  |  |  |  |  |  |  |
Payments for convertible bond hedges |  |  |  |  |  | $ 140,300,000 |  |  |  |  |  |  |  |  |
Warrant exercise price (USD per share) | $ / shares |  |  |  |  |  | $ 315.38 |  |  |  |  |  |  |  |  |
Warrant derivative in connection with Notes |  |  |  |  |  | $ 90,000,000.0 |  |  |  |  |  |  |  |  |
Proceeds from debt, net of issuance costs |  |  |  |  |  | 733,100,000 |  |  |  |  |  |  |  |  |
Debt issuance costs |  |  |  |  |  | $ 16,900,000 |  |  |  |  |  |  |  |  |
Convertible Notes | 2023 Convertible Senior Notes | Debt Instrument, Redemption, Period One |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Threshold trading days | d |  |  |  |  |  | 20 |  |  |  |  |  |  |  |  |
Consecutive trading days | d |  |  |  |  |  | 30 |  |  |  |  |  |  |  |  |
Stock price trigger to classify convertible debt as current (as a percent) |  |  |  |  |  | 130.00% |  |  |  |  |  |  |  |  |
Convertible Notes | 2023 Convertible Senior Notes | Debt Instrument, Redemption, Period Two |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Threshold trading days | d |  |  |  |  |  | 5 |  |  |  |  |  |  |  |  |
Consecutive trading days | d |  |  |  |  |  | 10 |  |  |  |  |  |  |  |  |
Maximum threshold of debt trading price trigger (as a percent) |  |  |  |  |  | 98.00% |  |  |  |  |  |  |  |  |
Convertible Bond Hedges | 2019 Convertible Senior Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Warrants issued in public offering (shares) | shares |  |  |  |  |  |  | 3,264,643 |  |  |  |  |  |  |  |
Exercise price of convertible bond hedge (USD per share) | $ / shares |  |  |  |  |  |  | $ 75.05 |  |  |  |  |  |  |  |
Payments for convertible bond hedges |  |  |  |  |  |  | $ 48,100,000 |  |  |  |  |  |  |  |
Gain (loss) on derivative |  |  |  |  |  |  |  |  |  | $ (1,900,000) |  |  | $ (11,000,000.0) |  |
Warrant exercise price (USD per share) | $ / shares |  |  |  |  |  |  | $ 125.08 |  |  |  |  |  |  |  |
Warrant derivative in connection with Notes |  |  |  |  |  |  | $ 11,600,000 |  |  |  |  |  |  |  |

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