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Cash Equivalents And Restricted Securities (Narrative) (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2016
Restricted Cash and Cash Equivalents Items [Line Items]          
Restricted securities $ 741   $ 741   $ 699
Gross realized gains or losses on cash equivalents 0 $ 0 0 $ 0  
Money Market Funds [Member]          
Restricted Cash and Cash Equivalents Items [Line Items]          
Restricted securities 741   741   699
Maturity Date Within Three Months [Member] | Money Market Funds [Member]          
Restricted Cash and Cash Equivalents Items [Line Items]          
Restricted securities         490
Maturity Date Between Three Months And One Year [Member] | Money Market Funds [Member]          
Restricted Cash and Cash Equivalents Items [Line Items]          
Restricted securities $ 741   $ 741   $ 209
Minimum [Member] | Maturity Date Between Three Months And One Year [Member] | Money Market Funds [Member]          
Restricted Cash and Cash Equivalents Items [Line Items]          
Restricted securities maturity period     3 months   3 months
Maximum [Member] | Maturity Date Within Three Months [Member] | Money Market Funds [Member]          
Restricted Cash and Cash Equivalents Items [Line Items]          
Restricted securities maturity period         3 months
Maximum [Member] | Maturity Date Between Three Months And One Year [Member] | Money Market Funds [Member]          
Restricted Cash and Cash Equivalents Items [Line Items]          
Restricted securities maturity period     1 year   1 year