Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net loss	$ (20,436)	$ (35,343)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation of property and equipment	216	306
Amortization of discount/premium on investments	(277)	(1,205)
Share-based compensation	2,717	6,440
Unrealized loss on equity investment	0	30
Lease-related amortization	(43)	(36)
Changes in operating assets and liabilities:
Accounts receivable	866	(444)
Prepaid expenses and other assets	809	399
Accounts payable and accrued liabilities	(2,546)	302
Net cash used in operating activities	(18,694)	(29,551)
Cash flows from investing activities:
Purchases of property and equipment	(11)	(150)
Purchases of short-term investments	(27,652)	(107,149)
Proceeds from sales of short-term investments	1,498	0
Proceeds from maturities of short-term investments	80,652	77,210
Net cash provided by (used in) investing activities	54,487	(30,089)
Cash flows from financing activities:
Proceeds from exercise of stock options	578	30
Proceeds from employee stock purchase plan	229	171
Payments of deferred offering costs	0	(23)
Net cash provided by financing activities	807	178
Net increase (decrease) in cash and cash equivalents	36,600	(59,462)
Cash and cash equivalents:
Beginning of period	16,901	81,106
End of period	$ 53,501	$ 21,644