Summary of Significant Accounting Policies (Details) - USD ($)	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Cash and cash equivalents and restricted cash reported within the condensed balance sheets
Cash and cash equivalents	$ 166,144,000	$ 114,504,000
Restricted cash	1,282,000	0
Cash, cash equivalents and restricted cash shown in the condensed consolidated statements of cash flows	$ 167,426,000	114,504,000	$ 125,886,000	$ 8,242,000
Convertible Preferred Stock Warrants
Warrants to purchase (in shares)	49,997
Reclassification of redeemable convertible preferred stock warrant liability to additional paid-in capital	$ 503,000
Prepaid expenses and other current assets
Other Income
Receivables under service agreements	356,000	282,000
Other current liabilities
Other Income
Contract liabilities	$ 92,000	$ 200,000