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Debt - Narrative (Details)
1 Months Ended 3 Months Ended 12 Months Ended
Nov. 30, 2018
USD ($)
d
$ / shares
shares
Jun. 30, 2017
USD ($)
$ / shares
Mar. 31, 2020
USD ($)
d
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2019
USD ($)
Dec. 19, 2018
USD ($)
Senior Notes | Senior convertible notes due 2023              
Debt Instrument [Line Items]              
Principal amount $ 850,000,000.0   $ 850,000,000.0     $ 850,000,000.0  
Interest rate on convertible notes (as a percent) 0.75%            
Proceeds from issuance of convertible debt, net of issuance costs $ 836,600,000            
Conversion ratio 0.0060869            
Conversion amount $ 1,000            
Conversion price of convertible notes (USD per share) | $ / shares $ 164.29            
Holder's repurchase price percentage in event of fundamental change (as a percent)     100.00%        
Number of trading days | d 60            
Proportion of conversion price (as a percent)     130.00%        
Redemption price (as a percent)     100.00%        
Stock counterparties to acquire with warrants purchased (shares) | shares 5,200,000            
Proceeds from sale of warrants $ 183,800,000            
Exercise price of warrants or rights (USD per share) | $ / shares $ 198.38            
Senior Notes | Senior convertible notes due 2022              
Debt Instrument [Line Items]              
Principal amount   $ 400,000,000.0 $ 400,000,000.0     $ 400,000,000.0  
Interest rate on convertible notes (as a percent)   0.75%          
Proceeds from issuance of convertible debt, net of issuance costs   $ 389,000,000.0          
Conversion ratio   0.0100918          
Conversion amount   $ 1,000          
Conversion price of convertible notes (USD per share) | $ / shares   $ 99.09          
Holder's repurchase price percentage in event of fundamental change (as a percent)     100.00%        
Proportion of conversion price (as a percent)     140.00%        
Redemption price (as a percent)     100.00%        
Line of Credit              
Debt Instrument [Line Items]              
Maximum borrowing capacity of revolving credit agreement     $ 200,000,000.0       $ 200,000,000.0
Option to increase revolving line of credit             $ 500,000,000.0
Value of unrestricted cash on hand threshold     $ 100,000,000.0        
Line of Credit | Minimum              
Debt Instrument [Line Items]              
Interest rate on convertible notes (as a percent)     0.375%        
Unused capacity fee (as a percent)     0.20%        
Line of Credit | Maximum              
Debt Instrument [Line Items]              
Interest rate on convertible notes (as a percent)     1.00%        
Unused capacity fee (as a percent)     0.30%        
Additional Paid-In Capital | Senior Notes | Senior convertible notes due 2023              
Debt Instrument [Line Items]              
Recognized additional paid-in capital from cash conversion option       $ 174,400,000      
Additional Paid-In Capital | Senior Notes | Senior convertible notes due 2022              
Debt Instrument [Line Items]              
Recognized additional paid-in capital from cash conversion option         $ 72,600,000    
Debt Instrument Conversion Term One | Senior Notes | Senior convertible notes due 2023 | Minimum              
Debt Instrument [Line Items]              
Number of trading days | d     20        
Proportion of applicable conversion price (as a percent)     130.00%        
Debt Instrument Conversion Term One | Senior Notes | Senior convertible notes due 2023 | Maximum              
Debt Instrument [Line Items]              
Number of trading days | d     30        
Debt Instrument Conversion Term One | Senior Notes | Senior convertible notes due 2022 | Minimum              
Debt Instrument [Line Items]              
Number of trading days | d     20        
Proportion of applicable conversion price (as a percent)     130.00%        
Debt Instrument Conversion Term One | Senior Notes | Senior convertible notes due 2022 | Maximum              
Debt Instrument [Line Items]              
Number of trading days | d     30        
Debt Instrument Conversion Term Two | Senior Notes | Senior convertible notes due 2023              
Debt Instrument [Line Items]              
Number of trading days | d     5        
Debt Instrument Conversion Term Two | Senior Notes | Senior convertible notes due 2023 | Maximum              
Debt Instrument [Line Items]              
Number of trading days | d     5        
Proportion of applicable conversion price (as a percent)     98.00%        
Debt Instrument Conversion Term Two | Senior Notes | Senior convertible notes due 2022              
Debt Instrument [Line Items]              
Number of trading days | d     5        
Debt Instrument Conversion Term Two | Senior Notes | Senior convertible notes due 2022 | Maximum              
Debt Instrument [Line Items]              
Number of trading days | d     5        
Proportion of applicable conversion price (as a percent)     98.00%        
Designated as Hedging Instrument | Senior Notes | Senior convertible notes due 2023              
Debt Instrument [Line Items]              
Stock issued upon conversion of senior notes (shares) | shares 5,200,000            
Equity component of convertible note issuance, net of issuance costs $ 218,900,000            
London Interbank Offered Rate (LIBOR) | Line of Credit | Minimum              
Debt Instrument [Line Items]              
Basis spread on variable rate (as a percent)     1.375%        
London Interbank Offered Rate (LIBOR) | Line of Credit | Maximum              
Debt Instrument [Line Items]              
Basis spread on variable rate (as a percent)     2.00%