Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Operating activities
Net loss	$ (23,912)	$ (19,968)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	2,079	953
Inventory step-up amortization	194
Reduction in the carrying amounts of right-of-use assets	108
Stock-based compensation expense	4,610	2,885
Non-cash interest expense	43	46
Loss on disposal of fixed assets	69	14
Changes in operating assets and liabilities:
Accounts receivable	1,445	(2,296)
Prepaid expenses and other assets	116	302
Inventory	(3,504)	(2,905)
Other non-current assets	27	2
Accounts payable	(959)	(1,600)
Accrued compensation and benefits, other accrued expenses and other current liabilities	(1,008)	669
Contract acquisition costs	(99)	(60)
Operating lease liabilities	387
Other non-current liabilities	(437)	9,448
Deferred revenue	241	(310)
Net cash used in operating activities	(20,600)	(12,820)
Investing activities
Purchases of property and equipment	(1,361)	(9,830)
Net cash used in investing activities	(1,361)	(9,830)
Financing activities
Proceeds from stock options exercised	1,111	1,910
Sale of common stock in at-the-market offering, net		48,019
Proceeds from ESPP purchase	440	393
Payments on notes payable	(75)	(50)
Net cash provided by financing activities	1,476	50,272
Net increase in cash and cash equivalents	(20,485)	27,622
Effect of foreign currency exchange rate on cash	110
Cash, restricted cash, and cash equivalents at beginning of period	110,181	45,429
Cash, restricted cash, and cash equivalents at end of period	89,806	73,051
Supplemental cash flow information
Cash paid for interest	155	160
Purchases of property and equipment included in accounts payable	35	279
Purchases of property and equipment included in other non-current liabilities		8,057
Reconciliation of cash, cash equivalents, and restricted cash:
Total cash, cash equivalents, and restricted cash	$ 89,806	$ 73,051