Annual and transition report of foreign private issuers pursuant to Section 13 or 15(d)

Equity (Movement in AOCI) (Details)

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Equity (Movement in AOCI) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Beginning balance $ (1,769) $ (6,307)
Total other comprehensive income (loss) 16,043 4,538
Ending balance 14,274 (1,769)
Net change in fair value of derivatives    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Beginning balance 5,972 (18)
Total other comprehensive income (loss) 14,918 5,990
Ending balance 20,890 5,972
Actuarial gain (loss) on pension obligations    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Beginning balance (7,741) (6,289)
Total other comprehensive income (loss) 1,125 (1,452)
Ending balance $ (6,616) $ (7,741)