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Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($)
 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2017
Mar. 31, 2017
Jun. 30, 2017
Dec. 31, 2016
Jan. 01, 2017
Dec. 31, 2015
Cost related to change in estimated fair value of leased instruments $ 300,000 $ 1,300,000        
Fair value assets liabilities transfer between levels     $ 0      
Future cash flows weighted average market yield 9.20%   9.20% 10.60%   10.60%
Deferred tax assets         $ 321,500,000  
Federal [Member]            
Excluded windfall tax deductions       $ 6,000,000    
State [Member]            
Excluded windfall tax deductions       $ 600,000