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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)

v3.19.3
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
Sep. 30, 2019
Dec. 31, 2018
Cash And Cash Equivalents And Short Term Investments [Line Items]    
Cash $ 2,968 $ 3,044
Short term investments Gross Unrealized Gains 13  
Short term investments Gross Unrealized Losses   (9)
Short term investments 21,001 20,169
Cash and cash equivalents and Short term investments, Amortized Cost 33,859 33,799
Cash and cash equivalents and Short term investments, Estimated Fair Value 33,872 33,790
Cash and cash equivalents 12,871 13,621
Level 1    
Cash And Cash Equivalents And Short Term Investments [Line Items]    
Short term investments Gross Unrealized Gains 4  
Cash equivalents and Short term investments, Estimated Fair Value 10,762 7,470
Cash equivalents and Short term investments, Amortized Cost 10,758 7,470
Level 2    
Cash And Cash Equivalents And Short Term Investments [Line Items]    
Short term investments Gross Unrealized Gains 9  
Short term investments Gross Unrealized Losses   (9)
Short term investments 17,142 18,181
Cash equivalents and Short term investments, Estimated Fair Value 20,142 23,276
Cash and cash equivalents 3,000 5,095
Cash equivalents and Short term investments, Amortized Cost 20,133 23,285
Money Market Funds | Level 1    
Cash And Cash Equivalents And Short Term Investments [Line Items]    
Cash equivalents 6,903 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 3,855 1,988
Short term investments Gross Unrealized Gains 4  
Short term investments 3,859 1,988
Commercial Paper | Level 2    
Cash And Cash Equivalents And Short Term Investments [Line Items]    
Cash equivalents   2,095
Short Term Investments Amortized Cost 9,641 10,639
Short term investments 9,641 8,544
Cash equivalents and Short term investments, Estimated Fair Value 9,641 10,639
Corporate Debt Securities | Level 2    
Cash And Cash Equivalents And Short Term Investments [Line Items]    
Short Term Investments Amortized Cost 3,740 5,964
Short term investments Gross Unrealized Gains 6  
Short term investments Gross Unrealized Losses   (7)
Short term investments 3,746 5,957
Asset-backed Securities | Level 2    
Cash And Cash Equivalents And Short Term Investments [Line Items]    
Short Term Investments Amortized Cost 3,752 3,682
Short term investments Gross Unrealized Gains 3  
Short term investments Gross Unrealized Losses   (2)
Short term investments 3,755 3,680
Cash equivalents and Short term investments, Estimated Fair Value $ 3,755 $ 3,680