CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net loss	$ (27,939)	$ (18,439)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	4,279	3,382
Noncash operating lease cost	1,048	673
Stock-based compensation expense	4,761	3,657
Loss on debt extinguishment		1,704
Change in fair value of convertible preferred stock warrant liability		1,403
Accretion of noncash interest and debt reduction		156
Other	63	73
Changes in operating assets and liabilities
Accounts receivable	(2,603)	(75)
Inventory and other deferred costs	(1,662)	(1,173)
Prepaid expenses and other current assets	(2,065)	(3,410)
Accounts payable	(1,628)	474
Accrued and other current liabilities	1,174	988
Contract liabilities	(15,383)	(9,170)
Operating lease liabilities	(637)	(717)
Other long-term liabilities	471
Net cash used in operating activities	(40,121)	(20,474)
Cash flows from investing activities:
Purchases of available-for-sale debt securities	(80,104)	(40,262)
Proceeds from maturities of available-for-sale debt securities	80,510
Purchases of property and equipment	(2,409)	(6,469)
Net cash used in investing activities	(2,003)	(46,731)
Cash flows from financing activities:
Proceeds from public offerings, net of underwriting discounts and commissions	117,500	144,025
Payments of costs related to public offerings	(93)	(3,950)
Proceeds from borrowings		20,000
Payments of borrowing costs		(490)
Repayments under borrowing arrangements		(25,000)
Debt extinguishment costs		(794)
Proceeds from exercise of common stock warrants		8
Proceeds from exercise or settlement of equity awards	2,920	678
Net cash provided by financing activities	120,327	134,477
Effect of exchange rates on cash flows and cash equivalents	(4)	(3)
Net change in cash and cash equivalents	78,199	67,269
Cash and cash equivalents, beginning of period	55,046	19,744
Cash and cash equivalents, end of period	$ 133,245	$ 87,013