v3.10.0.1
Schedule I, Condensed Financial Statements, Notes (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Profit/(Loss) Reconciliation [Abstract]        
Profit/(loss) for the period $ 41,596 $ (111,804) $ (4,855)  
Additional profit/(loss) if subsidiaries had been accounted for using the equity method of accounting as opposed to cost method 5,231 5,351 6,646  
Equity Reconciliation [Abstract]        
Shareholders equity 1,756,112 1,895,453 1,959,111 $ 2,023,501
Parent [Member]        
Basis of Presentation [Abstract]        
Cash dividend receivable from subsidiaries 0 10,383 29,737  
Profit/(Loss) Reconciliation [Abstract]        
Profit/(loss) for the period (184,443) 52,565 31,263  
Additional profit/(loss) if subsidiaries had been accounted for using the equity method of accounting as opposed to cost method 226,039 (164,369) (36,118)  
Equity Reconciliation [Abstract]        
Shareholders equity 1,769,146 2,087,059 2,153,420  
Additional shareholders equity if subsidiaries had been accounted for using the equity method of accounting as opposed to cost method $ (13,034) $ (191,606) $ (194,309)