v3.10.0.1
Corporate debt, Details of corporate debt (Details)
€ in Thousands, $ in Thousands
12 Months Ended
May 16, 2018
USD ($)
Feb. 10, 2017
EUR (€)
Swap
Dec. 22, 2014
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Jan. 31, 2019
USD ($)
May 10, 2018
USD ($)
Jul. 20, 2017
USD ($)
Jul. 20, 2017
EUR (€)
Dec. 03, 2014
USD ($)
Nov. 17, 2014
USD ($)
Corporate debt [Abstract]                        
Proceeds from corporate debt       $ 123,767 $ 296,398 $ 11,113            
Repayment of debt       385,964 613,242 182,636            
Amount drawn       $ 123,767 296,398 $ 11,113            
2019 Notes [Member]                        
Corporate debt [Abstract]                        
Principal amount                       $ 255,000
Fixed interest rate                       7.00%
Maturity date       November 15, 2019                
Former Revolving Credit Facility [Member]                        
Corporate debt [Abstract]                        
Proceeds from corporate debt     $ 125,000                  
Repayment of debt $ 54,000       $ 71,000              
Amount drawn     $ 125,000                  
Former Revolving Credit Facility [Member] | Top of Range [Member]                        
Corporate debt [Abstract]                        
Principal amount                     $ 125,000  
Note Issuance Facility [Member]                        
Corporate debt [Abstract]                        
Principal amount | €   € 275                    
Fixed interest rate   5.50%                    
Number of interest rate swaps | Swap   2                    
Note Issuance Facility [Member] | EURIBOR [Member]                        
Corporate debt [Abstract]                        
Adjustment to interest rate   4.90%                    
Series 1 Notes [Member]                        
Corporate debt [Abstract]                        
Maturity date       2022                
Series 2 Notes [Member]                        
Corporate debt [Abstract]                        
Maturity date       2023                
Series 3 Notes [Member]                        
Corporate debt [Abstract]                        
Maturity date       2024                
2017 Credit Facility [Member]                        
Corporate debt [Abstract]                        
Principal amount                 $ 11,500      
Maturity date       July 20, 2019                
2017 Credit Facility [Member] | Top of Range [Member]                        
Corporate debt [Abstract]                        
Principal amount | €                   € 10,000    
2017 Credit Facility [Member] | EURIBOR [Member]                        
Corporate debt [Abstract]                        
Adjustment to interest rate                 2.25% 2.25%    
2017 Credit Facility [Member] | LIBOR [Member]                        
Corporate debt [Abstract]                        
Adjustment to interest rate                 2.25% 2.25%    
New Revolving Credit Facility [Member]                        
Corporate debt [Abstract]                        
Maturity date       December 31, 2021                
Proceeds from corporate debt       $ 108                
Credit facility amount               $ 215        
Potential increase in borrowings capacity               $ 70        
Amount drawn       $ 108                
New Revolving Credit Facility [Member] | Subsequent Events [Member]                        
Corporate debt [Abstract]                        
Credit facility amount             $ 300          
Eurodollar Rate Loans [Member] | LIBOR [Member] | Bottom of Range [Member]                        
Corporate debt [Abstract]                        
Adjustment to interest rate               1.60%        
Eurodollar Rate Loans [Member] | LIBOR [Member] | Top of Range [Member]                        
Corporate debt [Abstract]                        
Adjustment to interest rate               2.25%        
Base Rate Loans [Member]                        
Corporate debt [Abstract]                        
Adjustment to interest rate               1.00%        
Base Rate Loans [Member] | Bottom of Range [Member]                        
Corporate debt [Abstract]                        
Adjustment to interest rate               0.60%        
Base Rate Loans [Member] | Top of Range [Member]                        
Corporate debt [Abstract]                        
Adjustment to interest rate               1.00%        
Base Rate Loans [Member] | Federal Funds Rate [Member]                        
Corporate debt [Abstract]                        
Adjustment to interest rate               0.50%