CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Cash flows from operating activities:
Net loss	$ (21,955)	$ (25,388)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation	230	170
Non-cash operating lease cost	473	437
Amortization of debt discount and other non-cash interest	253	231
Stock-based compensation	2,497	2,473
Change in operating assets and liabilities:
Accounts receivable	6,769	(4,674)
Prepaid expenses and other current assets	99	619
Inventory	(579)	(1,056)
Accounts payable	(1,332)	(3,206)
Accrued expenses and other current liabilities	(6,023)	(766)
Lease liabilities and other long-term liabilities	(312)	(10)
Net cash used in operating activities	(19,880)	(31,170)
Cash flows from investing activities:
Purchases of property and equipment	(292)	(444)
Net cash used in investing activities	(292)	(444)
Cash flows from financing activities:
Proceeds from common stock offerings, net of underwriters' discounts and offering cost	130,754
Payment of principal on finance lease	(8)	(10)
Proceeds from exercise of stock options and issuance of common stock under employee stock purchase plan	435	39
Net cash provided by financing activities	131,181	29
Net increase/(decrease) in cash and restricted cash:	111,009	(31,585)
Cash and restricted cash at beginning of period	98,031	183,104	$ 183,104
Cash and restricted cash at end of period	209,040	151,519	98,031
Reconciliation of cash and restricted cash:
Cash and restricted cash at end of period	209,040	151,519	$ 98,031	$ 209,040	$ 98,031	$ 151,519
Less restricted cash				(12,584)	(12,582)	(12,575)
Cash at end of period				$ 196,456	$ 85,449	$ 138,944
Non-cash investing and financing activities:
Right-of-use asset obtained in exchange for finance lease obligation		136
Purchases of property and equipment in accounts payable		409
Supplemental disclosure:
Cash paid for interest	$ 1,875	1,862
Right-of-use assets obtained in exchange of operating lease obligations		$ 1,878