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Commitments and Contingencies - Additional Information - Liquidity (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Debt Instrument [Line Items]      
Net operating cash flow $ 182,135 $ 544,264 $ 676,546
Working capital deficit (211,900)    
Current portion of long-term debt 242,137 800,897  
Carrying amount of long-term debt 3,363,127 3,449,611  
Senior Notes (8.5%) due January 15, 2020      
Debt Instrument [Line Items]      
Carrying amount of long-term debt $ 508,577 $ 592,657