Condensed Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Operating activities
Net loss	$ (34,045)	$ (24,884)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation expense	2,811	2,099
Share-based compensation expense	6,378	5,550
Intangible assets amortization	842	843
Investment amortization	(1,896)	(459)
Gain on equipment disposals	(79)	(41)
Fair value adjustment of convertible preferred stock warrant	2,266
Other	1	3
Changes in operating assets and liabilities:
Accounts receivable, net	(2,445)	1,165
Inventory	(166)	(2,921)
Prepaid expenses and other current assets	(883)	(364)
Accounts payable and accrued liabilities	1,314	(1,013)
Deferred rent	(480)	(359)
Deferred revenue	288,714	5,425
Other	1	(207)
Net cash provided by (used in) operating activities	262,333	(15,163)
Investing activities
Purchases of property and equipment	(5,354)	(1,614)
Proceeds from sales of equipment		19
Purchases of marketable securities	(358,671)	(110,947)
Proceeds from maturities of marketable securities	96,500	80,516
Net cash used in investing activities	(267,525)	(32,026)
Financing activities
Proceeds from exercise of stock options	1,989	923
Payment of deferred initial public offering costs	(3,360)
Other	(9)	(10)
Net cash (used in) provided by financing activities	(1,380)	913
Net decrease in cash, cash equivalents and restricted cash	(6,572)	(46,276)
Cash, cash equivalents and restricted cash at beginning of year	55,091	85,366
Cash, cash equivalents and restricted cash at end of period	48,519	39,090
Noncash investing and financing activities
Purchases of equipment included in accounts payable and accrued liabilities	1,490	$ 535
Deferred offering costs included in accounts payable and accrued expenses	$ 1,433