Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net loss	$ (2,262)	$ (623)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation, amortization, and accretion	664	1,423
Amortization expense - Right of use lease assets operating	426
Stock-based compensation	463	270
Loss on disposal of property and equipment	2
Changes in operating assets and liabilities:
Accounts receivable	898	1,796
Prepaid expenses and other assets	(10)	121
Materials inventory	76	(69)
Accounts payable	(489)	(554)
Accrued and other liabilities	(2,099)	(730)
Deferred revenue	(584)	56
Net cash (used in) provided by operating activities	(2,915)	1,690
Cash flows from investing activities:
Purchase of investments	(7,613)	(6,252)
Redemption of investments	6,122	3,070
Purchase of property and equipment	(134)	(194)
Net cash used in investing activities	(1,625)	(3,376)
Cash flows from financing activities:
Proceeds from exercise of common stock options	5	17
Net cash provided by financing activities	5	17
Net decrease in cash and cash equivalents	(4,535)	(1,669)
Cash and cash equivalents at beginning of period	8,351	6,090
Cash and cash equivalents at end of period	3,816	4,421
Supplemental disclosure of cash flow information:
Cash paid for income taxes, net of refunds received	1	1
Noncash investing/operating activities:
Transfer of property and equipment to materials inventory	23	30
Transfer of materials inventory to property and equipment	19	66
Additions to property, equipment and intangible assets not paid at the end of the period	$ 205	$ 88