Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Operating activities
Net loss	$ (18,592)	$ (48,709)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization expense	931	2,262
Stock-based compensation	2,288	5,441
Amortization of premium on investments, net	0	148
Gain on reduction of lease liability	1,839	0
Other	293	756
Change in operating assets and liabilities:
Contracts and other receivables	(1,115)	347
Prepaid materials	270	134
Prepaid expenses and other assets	(242)	630
Accounts payable	(393)	(4,029)
Accrued liabilities	(708)	(1,370)
Accrued compensation	75	(384)
Contract liabilities	(2,572)	2,428
Deferred rent	0	(1,252)
Other liabilities	(1,895)	325
Net cash used in operating activities	(19,821)	(43,273)
Investing activities
Purchases of short-term investments	0	0
Sales and maturities of short-term investments	0	46,541
Purchases of property and equipment	(221)	(22)
Sales of property and equipment	318	0
Acquisition of intangibles	(23)	0
Net cash provided by investing activities	74	46,519
Financing activities
Proceeds from issuance of securities through private placement, net of issuance costs	40,084	0
Proceeds from issuance of common stock, net	2,086	219
Proceeds from exercise of common stock options	3	1
Proceeds from financing leases	0	492
Payments on financing leases	(263)	(200)
Principal payments on term loan	(1,977)	(3,342)
Net cash provided by (used in) financing activities	39,933	(2,830)
Net increase in cash and cash equivalents	20,186	416
Cash and cash equivalents at beginning of period	13,935	13,519
Cash and cash equivalents at end of period	34,121	13,935
Supplemental disclosure of cash flow information
Interest paid	(1,655)	(2,073)
Income taxes paid	(1)	(1)
Supplemental disclosure of non-cash investing and financing activities
Non-cash acquisition of property and equipment	$ 3	$ 0