Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Summary of Components of Marketable Securities (Details)

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Summary of Significant Accounting Policies - Summary of Components of Marketable Securities (Details) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Amortizied cost $ 23,676  
Unrealized gain  
Unrealized loss 35  
Market value 23,641
U.S. Government Obligations [Member]    
Amortizied cost 6,455  
Unrealized gain  
Unrealized loss 1  
Market value 6,454  
Corporate Bonds and Commercial Paper [Member]    
Amortizied cost 17,221  
Unrealized gain  
Unrealized loss 34  
Market value $ 17,187