Condensed Statements of Cash Flows - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities
Net loss		$ (14,357)	$ (15,308)
Adjustments to reconcile net loss to net cash used in by operating activities:
Depreciation and amortization		153	221
Stock-based compensation		860	1,300
Amortization of debt issuance cost		179	51
Net amortization on investments		24	41
Changes in operating lease liabilities		79
Changes in assets and liabilities:
Accounts receivable		(385)	911
Inventories		(246)	(98)
Prepaid expenses and other assets		910	364
Accounts payable		423	(625)
Accrued and other liabilities		896	1,122
Contract research liabilities		(201)	(124)
Deferred revenue			(479)
Total adjustments		2,692	2,684
Net cash used in operating activities		(11,665)	(12,624)
Cash flows from investing activities
Purchases of property and equipment		(81)	(41)
Purchases of available-for-sale securities		(49)	(6,835)
Proceeds from maturities of available-for-sale securities		1,693	9,118
Net cash provided by investing activities		1,563	2,242
Cash flows from financing activities
Payments on equipment financing obligations		(5)	(6)
Payment of additional issuance cost for term loan			(105)
Net proceeds from issuances of common stock		15,406	18,456
Net cash provided by financing activities		15,401	18,345
Net decrease in Cash, cash equivalents, and restricted cash		5,299	7,963
Cash, cash equivalents, and restricted cash, beginning of the period		31,794	29,525
Cash, cash equivalents, and restricted cash, end of the period	[1]	37,093	37,488
Supplementary disclosure of non-cash financing information
Fully vested options issued to settle accrued liabilities		994	$ 1,860
Operating lease right-of-use assets obtained in exchange for operating lease obligations	[2]	$ 7,329

[1] Includes restricted cash of $150,000 (in long term restricted investments) included in the condensed balance sheets at both June 30, 2019 and June 30, 2018.

[2] Amounts for the six months ended June 30, 2019 include the transition adjustment for the adoption of Accounting Standards Update (“ASU”) No. 2016-02, Leases (Topic 842) (“Topic 842”).