CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Cash flows from operating activities:
Net loss	$ (45,267)	$ (49,213)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation	454	388
Non-cash operating lease cost	952	840
Amortization of debt discount and other non-cash interest	513	466
Stock-based compensation	5,271	5,094
Change in operating assets and liabilities:
Accounts receivable	7,282	(5,648)
Prepaid expenses and other current assets	1,351	1,106
Inventory	(1,306)	(3,955)
Accounts payable	(973)	(2,249)
Accrued expenses and other current liabilities	(6,782)	1,776
Lease liabilities and other long-term liabilities	(629)	(201)
Net cash used in operating activities	(39,134)	(51,596)
Cash flows from investing activities:
Purchases of property and equipment	(915)	(943)
Purchases of short-term investments	(56,535)
Net cash used in investing activities	(57,450)	(943)
Cash flows from financing activities:
Proceeds from common stock offerings, net of underwriters' discounts and offering cost	137,969
Payment of principal on finance lease	(16)	(20)
Proceeds from exercise of stock options and issuance of common stock under employee stock purchase plan	1,207	39
Net cash provided by financing activities	139,160	19
Net increase/(decrease) in cash and restricted cash:	42,576	(52,520)
Cash and restricted cash at beginning of period	98,031	183,104	$ 183,104
Cash and restricted cash at end of period	140,607	130,584	98,031
Reconciliation of cash and restricted cash:
Cash, cash equivalents, and restricted cash at end of period	140,607	130,584	183,104	$ 140,607	$ 98,031	$ 130,584
Less restricted cash				$ (12,584)	$ (12,582)	$ (12,578)
Cash and cash equivalents at end of period	128,023	118,006	$ 85,449
Non-cash investing and financing activities:
Right-of-use asset obtained in exchange for finance lease obligation		136
Supplemental disclosure:
Cash paid for interest	$ 3,749	3,683
Right-of-use assets obtained in exchange of operating lease obligations		$ 1,852