Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net loss	$ (23,205)	$ (21,437)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	213	300
Amortization of intangible assets	333	333
Stock-based compensation	5,038	5,060
Net premium amortization and discount on available-for-sale securities	(1)	(291)
Loss on disposal of fixed assets	119
Gain on government securities	(8)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	522	(1,129)
Right-of-use assets	198
Other long-term assets	129
Accounts payable	(758)	305
Accrued expenses	393	282
Lease liabilities	(110)
Other assets	(424)	(2,726)
Other current and non-current liabilities		2,279
Net cash used in operating activities	(17,561)	(17,024)
Cash flows from investing activities:
Purchases of property and equipment	(100)	(112)
Purchases of investments	(3,006)	(55,068)
Maturities of investments	17,000	32,000
Sales of investments	4,510
Net cash provided by (used) in investing activities	18,404	(23,180)
Cash flows from financing activities:
Proceeds from the issuance of common stock and warrants, net of issuance cost of $501	29,759
Proceeds from issuance of common stock under employee stock purchase plan	255	222
Tax payments related to shares withheld for vested restricted stock units		(613)
Proceeds from exercises of stock options	9	272
Net cash provided by (used in) financing activities	30,023	(119)
Net increase (decrease) in cash	30,866	(40,323)
Cash and cash equivalents at beginning of period	6,899	51,103
Cash and cash equivalents at end of period	37,765	10,780
Supplemental disclosure of noncash investing and financing activities:
Change in unrealized gains (losses) on available-for-sale securities	(4)	$ 23
Unpaid property and equipment included in accounts payable and accrued expenses	257
Issuance costs for rights offering in accounts payable	$ 261