Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net loss	$ (10,519)	$ (12,444)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation, amortization, and accretion	5,369	7,708
Stock-based compensation	1,221	2,936
(Gain) loss on disposal of property and equipment	70	(19)
Gain on disposal of intangible assets	(1,239)
Changes in operating assets and liabilities:
Accounts receivable	1,587	2,524
Prepaid expenses and other assets	402	118
Materials inventory	391	489
Accounts payable	688	(453)
Accrued and other liabilities	370	(2,088)
Deferred revenue	485	(471)
Net cash used in operating activities	(1,175)	(1,700)
Cash flows from investing activities:
Purchase of investments	(15,505)	(22,361)
Redemption of investments	20,014	23,526
Purchase of property and equipment	(705)	(2,130)
Proceeds from sale of equipment	12	22
Proceeds from sale of intangible assets	1,500
Purchased and capitalized intangible assets		(45)
Net cash (used in) provided by investing activities	5,316	(988)
Cash flows from financing activities:
Payment of capital leases	(13)	(7)
Proceeds from exercise of common stock options		714
Net cash (used in) provided by financing activities	(13)	707
Net increase (decrease) in cash and cash equivalents	4,128	(1,981)
Cash and cash equivalents at beginning of period	5,759	11,676
Cash and cash equivalents at end of period	9,887	9,695
Supplemental disclosure of cash flow information:
Cash paid for interest	6	5
Cash paid for income taxes, net of refunds received	1	7
Noncash investing/operating activities:
Transfer of property and equipment to materials inventory	380	752
Transfer of materials inventory to property and equipment	351	1,335
Additions to property, equipment and intangible assets not paid at the end of the period	$ 49	$ 72