Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities:
Net loss	$ (8,691)	$ (5,669)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation, amortization, and accretion	3,597	3,823
Stock-based compensation	978	2,049
Gain on disposal of property and equipment	(7)	(19)
Gain on disposal of intangible assets	(1,239)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	254	404
Materials inventory	373	426
Accounts receivable	2,221	1,343
Accounts payable	743	(211)
Accrued and other liabilities	4	(1,888)
Deferred revenue	211	(137)
Net cash (used in) provided by operating activities	(1,556)	121
Cash flows from investing activities:
Purchase of investments	(11,897)	(13,262)
Redemption of investments	13,215	18,916
Purchase of property and equipment	(521)	(1,786)
Proceeds from sale of equipment	10	22
Proceeds from sale of intangible assets	1,500
Purchased and capitalized intangible assets		(45)
Net cash provided by investing activities	2,307	3,845
Cash flows from financing activities:
Payment of capital leases	(11)
Proceeds from exercise of common stock options		714
Net cash (used in) provided by financing activities	(11)	714
Net increase in cash and cash equivalents	740	4,680
Cash and cash equivalents at beginning of period	5,759	11,676
Cash and cash equivalents at end of period	6,499	16,356
Supplemental disclosure of cash flow information:
Cash paid for interest	5
Cash paid for income taxes, net of refunds received	1	4
Noncash investing/operating activities:
Transfer of property and equipment to materials inventory	218	588
Transfer of materials inventory to property and equipment	232	1,211
Additions to property, equipment and intangible assets not paid at the end of the period	$ 147	$ 316