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Summary of Significant Accounting Policies Organization (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Income Tax Expense (Benefit) $ 9,892 $ 16,273    
Total stockholders' equity (deficit) 1,117,562 981,723 $ 1,097,227 $ 930,180
Deferred income taxes 94,381   86,657  
Accrued liabilities 280,076   255,146  
Adjustments [Member]        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Income Tax Expense (Benefit)   $ 0    
Total stockholders' equity (deficit)     3,800  
Deferred income taxes     2,400  
Accrued liabilities     $ 6,200  
Adjustments for Change in Accounting Principle [Member]        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Income Tax Expense (Benefit) $ 300