Quarterly report pursuant to Section 13 or 15(d)

Debt (Convertible) (Details)

v3.19.1
Debt (Convertible) (Details)
 1 Months Ended 12 Months Ended
May 31, 2018
USD ($)
days
$ / shares
Dec. 31, 2014
USD ($)
$ / shares
Mar. 31, 2019
USD ($)
$ / shares
Dec. 31, 2018
USD ($)
Mar. 31, 2018
Convertible Notes due 2019          
Debt Instrument [Line Items]          
Interest rate (as a percent)   1.75%      
Repurchase percentage of principal (as a percent)   100.00%      
Conversion rate   15.9022      
Principal amount   $ 1,000      
Conversion price (in dollars per share)   $ 62.88 $ 62.88    
Effective interest rate (as a percent)     6.00%   6.00%
Face amount | $   $ 172,500,000 $ 172,500,000 $ 172,500,000  
Convertible notes due 2023          
Debt Instrument [Line Items]          
Interest rate (as a percent) 1.75%        
Repurchase percentage of principal (as a percent) 100.00%        
Conversion rate 14.6381        
Principal amount $ 1,000        
Conversion price (in dollars per share) $ 68.31   $ 68.31    
Effective interest rate (as a percent)     6.00%    
Face amount | $ $ 345,000,000        
Threshold percentage of stock price trigger (as a percent) 130.00%        
Threshold trading days (in days) | days 20        
Consecutive trading days | days 30        
Preceding Days | days 5