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Basis of Presentation and Summary of Significant Accounting Policies - Derivatives (Details) - Convertible Notes - 2019 Convertible Senior Notes | Mar. 31, 2019 yr $ / shares | Aug. 31, 2014 $ / shares
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Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Common stock price (USD per share) | $ 125.71 |
Exercise price, conversion premium and bond hedge (USD per share) | $ 75.05 | $ 75.05
Risk-free interest rate |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Measurement input (as a percent) | 0.0246 |
Volatility |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Measurement input (as a percent) | 0.35 |
Dividend yield |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Measurement input (as a percent) | 0 |
Annual coupon rate |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Measurement input (as a percent) | 0.0075 |
Remaining contractual term (in years) |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Measurement input (as a percent) | yr | 0.38 |

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