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Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($)
 3 Months Ended 12 Months Ended
Mar. 31, 2017
Dec. 31, 2016
Jan. 01, 2017
Dec. 31, 2015
Cost related to change in estimated fair value of leased instruments $ 1,300,000      
Fair value assets liabilities transfer between levels $ 0      
Future cash flows weighted average market yield 10.10% 10.60%   13.50%
Deferred tax assets     $ 321,500,000  
Cash, cash equivalents and investments $ 56,100,000 $ 72,000,000    
Federal [Member]        
Excluded windfall tax deductions   6,000,000    
State [Member]        
Excluded windfall tax deductions   $ 600,000