Annual report pursuant to Section 13 and 15(d)

Cash, Cash Equivalents and Short-Term Investments - Schedule of Cash and Cash Equivalents and Short-term Investments by Significant Investment Category (Details)

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Cash, Cash Equivalents and Short-Term Investments - Schedule of Cash and Cash Equivalents and Short-term Investments by Significant Investment Category (Details) - USD ($)
$ in Thousands
Dec. 31, 2019
Dec. 31, 2018
Cash And Cash Equivalents And Short Term Investments [Line Items]    
Cash $ 3,950 $ 3,044
Short term investments Gross Unrealized Gains 10  
Short term investments Gross Unrealized Losses (2) (10)
Short term investments 21,686 20,169
Cash and cash equivalents and Short term investments, Amortized Cost 34,875 33,799
Cash and cash equivalents and Short term investments, Estimated Fair Value 34,883 33,790
Cash and cash equivalents 13,197 13,621
Level 1    
Cash And Cash Equivalents And Short Term Investments [Line Items]    
Short term investments Gross Unrealized Gains 2  
Short term investments Gross Unrealized Losses (1)  
Cash equivalents and Short term investments, Estimated Fair Value 8,579 7,470
Cash equivalents and Short term investments, Amortized Cost 8,578 7,470
Level 2    
Cash And Cash Equivalents And Short Term Investments [Line Items]    
Short term investments Gross Unrealized Gains 8  
Short term investments Gross Unrealized Losses (1) (10)
Short term investments 18,607 18,181
Cash equivalents and Short term investments, Estimated Fair Value 22,354 23,276
Cash and cash equivalents 3,747 5,095
Cash equivalents and Short term investments, Amortized Cost 22,347 23,285
Money Market Funds | Level 1    
Cash And Cash Equivalents And Short Term Investments [Line Items]    
Cash equivalents 5,500 5,482
Repurchase Agreements | Level 2    
Cash And Cash Equivalents And Short Term Investments [Line Items]    
Cash equivalents 3,000 3,000
US Treasury Securities | Level 1    
Cash And Cash Equivalents And Short Term Investments [Line Items]    
Short Term Investments Amortized Cost 3,078 1,988
Short term investments Gross Unrealized Gains 2  
Short term investments Gross Unrealized Losses (1)  
Short term investments 3,079 1,988
Commercial Paper | Level 2    
Cash And Cash Equivalents And Short Term Investments [Line Items]    
Cash equivalents 747 2,095
Short Term Investments Amortized Cost 8,920 10,639
Short term investments 8,173 8,544
Cash equivalents and Short term investments, Estimated Fair Value 8,920 10,639
Corporate Debt Securities | Level 2    
Cash And Cash Equivalents And Short Term Investments [Line Items]    
Short Term Investments Amortized Cost 5,922 5,964
Short term investments Gross Unrealized Gains 5  
Short term investments Gross Unrealized Losses (1) (7)
Short term investments 5,926 5,957
Asset-backed Securities | Level 2    
Cash And Cash Equivalents And Short Term Investments [Line Items]    
Short Term Investments Amortized Cost 4,505 3,682
Short term investments Gross Unrealized Gains 3  
Short term investments Gross Unrealized Losses   (3)
Short term investments 4,508 3,680
Cash equivalents and Short term investments, Estimated Fair Value $ 4,508 $ 3,680