Quarterly report pursuant to Section 13 or 15(d)

Fair Value of Financial Instruments - Hierarchy Table (Details)

v3.19.3
Fair Value of Financial Instruments - Hierarchy Table (Details) - USD ($)
$ in Thousands
9 Months Ended 12 Months Ended
Sep. 30, 2019
Dec. 31, 2018
Fair value    
Unrealized Gains $ 4  
Unrealized Losses   $ (9)
Transfers between Level 2 and Level 3 0 0
Letter of credit collateral 1,300  
Adjusted cost    
Fair value    
Cash and Cash Equivalents, Fair Value Disclosure 3,348 10,992
Assets, Fair Value Disclosure 46,020 62,794
Fair Value    
Fair value    
Cash and Cash Equivalents, Fair Value Disclosure 3,348 10,992
Assets, Fair Value Disclosure 46,024 62,785
Cash and Cash Equivalents | Fair Value    
Fair value    
Cash and Cash Equivalents, Fair Value Disclosure 2,040 9,689
Assets, Fair Value Disclosure 29,255 32,892
Restricted Cash | Fair Value    
Fair value    
Cash and Cash Equivalents, Fair Value Disclosure 1,308 1,303
Assets, Fair Value Disclosure 1,308 1,303
Marketable Securities | Fair Value    
Fair value    
Assets, Fair Value Disclosure 15,461 28,590
Level 1    
Fair value    
Unrealized Gains 4  
Unrealized Losses   (4)
Level 1 | Adjusted cost    
Fair value    
Investments, Fair Value Disclosure 37,672 42,141
Level 1 | Fair Value    
Fair value    
Investments, Fair Value Disclosure 37,676 42,137
Level 1 | Money market funds | Adjusted cost    
Fair value    
Investments, Fair Value Disclosure 15,240 23,203
Level 1 | Money market funds | Fair Value    
Fair value    
Investments, Fair Value Disclosure 15,240 23,203
Level 1 | U.S. treasury securities    
Fair value    
Unrealized Gains 4  
Unrealized Losses   (4)
Level 1 | U.S. treasury securities | Adjusted cost    
Fair value    
Investments, Fair Value Disclosure 22,432 18,938
Level 1 | U.S. treasury securities | Fair Value    
Fair value    
Investments, Fair Value Disclosure 22,436 18,934
Level 1 | Cash and Cash Equivalents | Fair Value    
Fair value    
Investments, Fair Value Disclosure 27,215 23,203
Level 1 | Cash and Cash Equivalents | Money market funds | Fair Value    
Fair value    
Investments, Fair Value Disclosure 15,240 23,203
Level 1 | Cash and Cash Equivalents | U.S. treasury securities | Fair Value    
Fair value    
Investments, Fair Value Disclosure 11,975  
Level 1 | Marketable Securities | Fair Value    
Fair value    
Investments, Fair Value Disclosure 10,461 18,934
Level 1 | Marketable Securities | U.S. treasury securities | Fair Value    
Fair value    
Investments, Fair Value Disclosure 10,461 18,934
Level 2 | U.S. government agency securities    
Fair value    
Unrealized Losses   (5)
Level 2 | U.S. government agency securities | Adjusted cost    
Fair value    
Investments, Fair Value Disclosure 5,000 9,661
Level 2 | U.S. government agency securities | Fair Value    
Fair value    
Investments, Fair Value Disclosure 5,000 9,656
Level 2 | Marketable Securities | U.S. government agency securities | Fair Value    
Fair value    
Investments, Fair Value Disclosure $ 5,000 $ 9,656