Quarterly report pursuant to Section 13 or 15(d)

Debt (Convertible) (Details)

v3.10.0.1
Debt (Convertible) (Details)
$ / shares in Units, $ in Thousands
May 25, 2018
USD ($)
days
$ / shares
Dec. 15, 2014
USD ($)
$ / shares
Sep. 30, 2018
$ / shares
Dec. 31, 2017
$ / shares
Sep. 30, 2017
Convertible Notes due 2019          
Debt Instrument [Line Items]          
Face amount and over allotments | $   $ 172,500      
Interest rate (as a percent)   1.75%      
Repurchase percentage of principal (as a percent)   100.00%      
Conversion rate   15.9022      
Principal amount   $ 1      
Conversion price (in dollars per share)   $ 62.88 $ 62.88 $ 68.31  
Effective interest rate (as a percent)     6.00%   6.00%
Convertible notes due 2023          
Debt Instrument [Line Items]          
Face amount and over allotments | $ $ 345,000        
Interest rate (as a percent) 1.75%        
Repurchase percentage of principal (as a percent) 100.00%        
Conversion rate 14.6381        
Principal amount $ 1        
Conversion price (in dollars per share) $ 68.31        
Effective interest rate (as a percent)     6.00%    
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