CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Operating activities:
Net loss	$ (29,031)	$ (24,345)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	3,476	3,374
Non-cash interest expense	2,533	2,201
Depreciation and amortization	402	377
Changes in operating assets and liabilities:
Receivables	11,068	(1,900)
Inventory	(64)	(648)
Prepaid expenses and other assets	628	2,110
Accounts payable and accrued expenses	1,847	5,883
Net cash used in operating activities	(9,141)	(12,948)	$ (60,100)
Investing activities:
Purchases of property and equipment	(66)	(182)
Purchases of investments	(3,176)	(281)
Proceeds from the sale and maturities of investments	14,018	11,750
Net cash provided by investing activities	10,776	11,287
Financing activities:
Proceeds upon exercise of stock options	2,712	108
Principal payments on finance lease liabilities	(313)	(254)
Net cash provided by (used in) financing activities	2,399	(146)
Net increase (decrease) in cash and cash equivalents	4,034	(1,807)
Cash and cash equivalents at beginning of period	3,084	5,861	5,861
Cash and cash equivalents at end of period	7,118	4,054	$ 3,084
Supplemental cash flow information
Cash paid for interest	89	$ 82
Property acquired under finance lease	$ 22