Condensed Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities
Net loss	$ (18,786)	$ (17,042)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	747	469
Amortization of operating lease right-of-use assets	399
Depreciation	361	391
Deferred rent	0	515
Other	42	45
Change in operating assets and liabilities
Prepaid expenses and other assets	(657)	635
Accounts payable	635	615
Accrued compensation and other accrued liabilities	(904)	(21)
Operating lease liabilities	(451)
Net cash used in operating activities	(18,614)	(14,393)
Cash flows from investing activities
Proceeds from maturities of marketable securities	13,900	16,000
Purchases of marketable securities	(3,476)	(37,475)
Purchases of property and equipment	(6,213)	(2,106)
Net cash provided by (used in) investing activities	4,211	(23,581)
Cash flows used in financing activities
Proceeds from public offering of securities, net of underwriting commissions and offering costs	18,472	45,603
Proceeds from build-to-suit obligation, net of issuance costs	2,277	0
Principal payments on financing obligations	(1,234)	(3,083)
Net cash provided by financing activities	19,515	42,520
Net increase in cash, cash equivalents and restricted cash	5,112	4,546
Cash, cash equivalents and restricted cash at beginning of period	9,595	11,686
Cash, cash equivalents and restricted cash at end of period	14,707	16,232
Supplemental cash flow information
Cash paid for interest	365	203
Cash paid for taxes	1	0
Non-cash investing and financing activities
Total	851
Acquisition of property and equipment under accounts payable and other accrued liabilities	5,795	264
Accrued offering costs	142	98
Right-of-use assets acquired under finance lease obligations	$ 22	$ 0