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Debt - Convertible Notes (Details)
1 Months Ended 12 Months Ended
Sep. 04, 2019
$ / shares
$ / unit
Sep. 30, 2019
USD ($)
d
$ / shares
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Debt Instrument [Line Items]          
Debt instrument trading days | d   20      
Debt instrument consecutive trading day | d   30      
Debt issuance costs related with equity component of convertible debt     $ 0 $ 0 $ 403,000
Premiums for capped call options   $ 32,900,000 32,890,000    
Interest expense     15,300,000 $ 2,500,000  
Call Option          
Debt Instrument [Line Items]          
Capped price (in dollars per share) | $ / unit 37.00        
Premium of cap price as a percentage of closing price 100.00%        
Convertible debt          
Debt Instrument [Line Items]          
Interest expense     7,700,000    
Convertible debt | Convertible Senior Notes Due 2024          
Debt Instrument [Line Items]          
Principal amount   $ 316,250,000 316,250,000    
Debt instrument, interest rate percentage   1.50%      
Debt instrument, effective conversion price (in dollars per share) | $ / shares $ 24.98        
Stock price trigger, premium on closing price (as a percent) 35.00%        
Redemption price (as a percent) 100.00% 100.00%      
Stock price trigger (as a percent)   130.00%      
Debt issuance costs incurred     9,200,000    
Debt issuance costs, net     5,500,000    
Debt issuance costs related with equity component of convertible debt     3,700,000    
Equity component of convertible debt   $ 128,400,000 $ 128,400,000    
Convertible debt | Convertible Senior Notes Due 2024 | LEVEL 3          
Debt Instrument [Line Items]          
Convertible notes fair value of liability component   $ 187,900,000      
Common Stock          
Debt Instrument [Line Items]          
Closing stock price (in dollars per share) | $ / shares $ 18.50        
Common Stock | Convertible debt | Convertible Senior Notes Due 2024          
Debt Instrument [Line Items]          
Debt instrument, conversion price (in dollars per share) | $ / shares   $ 0.04004