Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018
Operating Activities
Net loss		$ (41,568)	$ (19,218)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense		2,533	1,866
Depreciation and amortization		112	106
Loss on disposal of property and equipment			116
Changes in operating assets and liabilities:
Prepaid and other current assets		(477)	(2,429)
Accounts payable		875	(378)
Accrued compensation and other accrued liabilities		2,944	234
Operating lease liability and right-of-use assets		57
Deferred rent			167
Deferred revenue			(6)
Net cash flows used in operating activities		(35,524)	(19,542)
Investing Activities
Proceeds from maturities of short-term investments		133,967	60,337
Purchase of short-term investments		(106,950)	(135,612)
Purchases of property and equipment		(65)	(201)
Net cash flows provided by (used in) investing activities		26,952	(75,476)
Financing Activities
Payments for the redemption of redeemable convertible notes			(5,082)
Issuance of common stock for secondary public offering, net of issuance costs			106,762
Issuance of common stock from stock grants and option exercises		327	36
Proceeds from exercise of warrants			9,545
Net cash flow provided by financing activities		327	111,261
Net (decrease) increase in cash, cash equivalents and restricted cash		(8,245)	16,243
Cash, cash equivalents and restricted cash at beginning of the period		31,263	19,805
Cash, cash equivalents and restricted cash at end of the period	[1]	23,018	36,048
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Adoption of ASC 606			207
Conversion of redeemable convertible notes to common stock			3
Unrealized gain on investments		35	$ (24)
Right-of-use asset and operating lease liability recorded upon the adoption of ASC 842, net		$ 2,052

[1] The following table provides a reconciliation of cash, cash equivalents and restricted cash to amounts reported within the condensed consolidated balance sheets: