Derivative financial instruments, Breakdown of fair value amounts (Details) - Interest Rate Derivatives [Member] - USD ($) $ in Thousands |
12 Months Ended | |
|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| Euros [Member] | ||
| Breakdown of fair value amount of derivative financial instruments [Abstract] | ||
| Percent of notional amount of debt hedged in next 12 months | 100.00% | |
| Percentage of notional amount of debt hedged in year two | 75.00% | |
| Cash Flow Hedge [Member] | ||
| Breakdown of fair value amount of derivative financial instruments [Abstract] | ||
| Assets | $ 11,571 | $ 8,230 |
| Liabilities | $ 279,152 | $ 329,731 |