CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net loss	$ (28,071)	$ (33,155)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	232	422
Amortization of deferred financing costs	169	157
Amortization of deferred compensation for services	47	77
Amortization of (discount) premium on investment securities	15	157
Non-cash lease expense	842	607
Stock-based compensation	3,722	3,087
Change in derivative liabilities	15	36
Debt refinancing costs	102	0
Gain on sale of equipment	(710)	0
Non-cash interest associated with debt discount accretion	109	70
Changes in operating assets and liabilities:
Accounts receivable	(3,892)	(5,783)
Inventory	(3,487)	0
Prepaid expenses and other assets	(307)	(13,662)
Accounts payable	753	(248)
Accrued compensation and benefits	882	(1,324)
Operating lease liabilities	(836)	(721)
Accrued and other liabilities	(1,041)	7,517
Deferred revenue	3,836	(1,454)
Net cash used in operating activities	(27,620)	(44,217)
Investing activities
Proceeds from maturities and redemptions of investments	27,300	35,370
Purchases of investments	(25,763)	(32,107)
Proceeds from sale of equipment	795	0
Purchases of property and equipment	0	(778)
Net cash provided by investing activities	2,332	2,485
Financing activities
Proceeds from 2022 Loan, net of issuance costs	26,971	0
Repayment of 2018 Loan, net of settlement costs	(33,038)	0
Proceeds from issuance of common stock in at the market offering, net of issuance costs	5,921	34,272
Proceeds from issuance of common stock under equity incentive and stock purchase plans	83	498
Net cash provided by (used in) financing activities	(63)	34,770
Net decrease in cash and cash equivalents	(25,351)	(6,962)
Cash and cash equivalents at beginning of period	72,428	91,032
Cash and cash equivalents at end of period	47,077	84,070
Supplementary disclosure of cash flow information:
Cash paid for interest	741	963
Cash paid for income taxes	1	0
Supplementary disclosure of non-cash activities:
Right-of-use assets obtained in exchange for lease obligations	0	450
Issuance of derivative in connection with issuance of loan payable	$ 375	$ 0