STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (37,589)	$ (35,358)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	1,612	1,178
Change in operating lease right-of-use assets	841
Depreciation	683	764
Effective interest on financing obligations	860	304
Capitalized interest	(582)	(294)
Accretion of interest on marketable securities	(55)	(131)
Deferred rent	0	936
Impairment loss	0	511
Other	93	(14)
Change in operating assets and liabilities:
Prepaid expenses and other assets	(193)	1,208
Accounts payable	1,764	98
Accrued compensation and other accrued liabilities	(1,288)	1,676
Operating lease liabilities	(963)
Net cash used in operating activities	(34,817)	(29,122)
Cash flows from investing activities:
Proceeds from maturities of marketable securities	17,400	16,050
Purchases of marketable securities	(3,476)	(29,788)
Purchases of property and equipment	(11,760)	(5,490)
Proceeds from sale of property and equipment	0	15
Net cash provided by (used in) investing activities	2,164	(19,213)
Cash flows from financing activities:
Proceeds from build-to-suit obligation, net of issuance costs	6,126	7,570
Principal payments on financing obligations	(3,079)	(6,999)
Payment of term loan end of term charge	0	(351)
Net cash provided by financing activities	29,829	45,824
Net decrease in cash, cash equivalents and restricted cash	(2,824)	(2,511)
Cash, cash equivalents and restricted cash at beginning of year	9,595	12,106
Cash, cash equivalents and restricted cash at end of year	6,771	9,595
Supplemental cash flow information:
Cash paid for interest	834	884
Cash paid for income taxes	3	2
Non-cash investing and financing activities:
Acquisition of property and equipment under accounts payable and other accrued liabilities	4,420	3,374
Accrued offering costs	188	0
Right-of-use assets acquired under finance lease obligations	22
Right-of-use assets acquired under finance lease obligations		25
Issuance of common stock warrants in connection with a build-to-suit obligation	0	243
Public Stock Offering
Cash flows from financing activities:
Proceeds from public offering of securities, net of commissions and offering costs	18,331	45,604
At-The-Market Offering
Cash flows from financing activities:
Proceeds from public offering of securities, net of commissions and offering costs	5,289	0
Registered Direct Offering
Cash flows from financing activities:
Proceeds from public offering of securities, net of commissions and offering costs	$ 3,162	$ 0