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Cash And Cash Equivalents And Marketable Securities (Cash, Cash Equivalents And Marketable Securities) (Details) - USD ($)
$ in Thousands
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]        
Available-for-sale securities, Amortized Cost Basis $ 2,099      
Cash and cash equivalents 16,615 $ 31,299 $ 40,590 $ 48,588
Cash and cash equivalents, Short Term Investment, Amortized Cost 18,714 31,299    
Cash and cash equivalents, Short Term Investment Unrealized Gains   1    
Cash and cash equivalents, Short Term Investment Unrealized Losses (1)    
Available-for-sale securities, Gross Unrealized Losses    
Accrued Interest    
Estimated Fair Value, Marketable securities 2,099      
Cash and cash equivalents, Short Term Investment, Fair Value 18,714 31,299    
Estimated Fair Value, Fair Value Disclosure [Member]        
Schedule of Available-for-sale Securities [Line Items]        
Estimated Fair Value, Marketable securities 2,099      
Cash and cash equivalents, Short Term Investment, Fair Value 18,714 31,299    
Cash [Member]        
Schedule of Available-for-sale Securities [Line Items]        
Cash 1,434 273    
Available-for-sale securities, Gross Unrealized Losses    
Accrued Interest    
Cash and cash equivalents, Fair Value 1,434 273    
Cash [Member] | Estimated Fair Value, Fair Value Disclosure [Member]        
Schedule of Available-for-sale Securities [Line Items]        
Cash and cash equivalents, Fair Value 1,434 273    
Cash Equivalents [Member]        
Schedule of Available-for-sale Securities [Line Items]        
Cash equivalents 12,783 22,630    
Available-for-sale securities, Gross Unrealized Losses    
Accrued Interest    
Cash and cash equivalents, Fair Value 12,783 22,630    
Cash Equivalents [Member] | Estimated Fair Value, Fair Value Disclosure [Member]        
Schedule of Available-for-sale Securities [Line Items]        
Cash and cash equivalents, Fair Value 12,783 22,630    
Commercial Paper [Member]        
Schedule of Available-for-sale Securities [Line Items]        
Available-for-sale securities, Amortized Cost Basis 4,497 8,396    
Available-for-sale securities, Gross Unrealized Gains   1    
Available-for-sale securities, Gross Unrealized Losses (1)    
Accrued Interest    
Estimated Fair Value, Marketable securities 4,497 8,396    
Commercial Paper [Member] | Estimated Fair Value, Fair Value Disclosure [Member]        
Schedule of Available-for-sale Securities [Line Items]        
Estimated Fair Value, Marketable securities 4,497 8,396    
Corporate Securities [Member]        
Schedule of Available-for-sale Securities [Line Items]        
Available-for-sale securities, Gross Unrealized Losses      
Accrued Interest      
Cash And Cash Equivalents, Reported Value [Member]        
Schedule of Available-for-sale Securities [Line Items]        
Cash and cash equivalents 16,615 31,299    
Available-for-sale securities, Gross Unrealized Gains   1    
Available-for-sale securities, Gross Unrealized Losses (1)    
Accrued Interest    
Cash and cash equivalents, Fair Value 16,615 31,299    
Cash And Cash Equivalents, Reported Value [Member] | Estimated Fair Value, Fair Value Disclosure [Member]        
Schedule of Available-for-sale Securities [Line Items]        
Cash and cash equivalents, Fair Value 16,615 31,299    
Matures In One Year Or Less [Member]        
Schedule of Available-for-sale Securities [Line Items]        
Cash and cash equivalents, Short Term Investment, Amortized Cost 18,714 31,299    
Available-for-sale securities, Gross Unrealized Gains   1    
Available-for-sale securities, Gross Unrealized Losses (1)    
Accrued Interest    
Cash and cash equivalents, Short Term Investment, Fair Value 18,714 31,299    
Matures In One Year Or Less [Member] | Estimated Fair Value, Fair Value Disclosure [Member]        
Schedule of Available-for-sale Securities [Line Items]        
Cash and cash equivalents, Short Term Investment, Fair Value 18,714 31,299    
Matures One To Three Years [Member]        
Schedule of Available-for-sale Securities [Line Items]        
Available-for-sale securities, Gross Unrealized Losses    
Accrued Interest