Summary of Significant Accounting Policies (Details)	1 Months Ended	3 Months Ended
	Feb. 29, 2020	Mar. 31, 2020 USD ($) Institution shares	Dec. 31, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Cash and cash equivalents and restricted cash reported within the condensed balance sheets
Cash and cash equivalents		$ 92,183,000	$ 157,954,000
Restricted cash		1,282,000	1,282,000
Cash, cash equivalents and restricted cash shown in the consolidated statements of cash flows		$ 93,465,000	159,236,000	$ 27,043,000	$ 114,504,000
Convertible Preferred Stock Warrants
Warrants to purchase (in shares) | shares		49,997
Reclassification of redeemable convertible preferred stock warrant liability to additional paid-in capital		$ 500,000
Concentration of credit risk
Number of financial institutions holding cash and cash and cash equivients | Institution		2
Prepaid expenses and other current assets
Other Income
Receivables under service agreements		$ 215,000	237,000
Other current liabilities and other non-current liabilities
Other Income
Contract liabilities			$ 0
Other current liabilities
Other Income
Contract liabilities		1,400,000
Other noncurrent liabilities
Other Income
Contract liabilities		$ 500,000
Other income
Other Income
Expected service period	18 months