Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net loss	$ (15,437)	$ (21,013)	$ (21,761)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation, amortization, and accretion	9,537	10,728	11,577
Stock-based compensation	3,627	5,673	6,021
(Gain) loss on disposal of property and equipment	(12)	18
Realized loss from investment		8
Changes in operating assets and liabilities:
Prepaid expenses and other assets	122	(42)	94
Materials inventory	333	(319)	1,581
Accounts receivable	1,051	(793)	1,701
Accounts payable	(493)	(24)	(635)
Accrued and other liabilities	(3,069)	2,985	(1,769)
Deferred revenue	(1,063)	(1,217)	895
Related party deferred revenue		(831)	446
Net cash used in operating activities	(5,404)	(4,827)	(1,850)
Cash flows from investing activities:
Purchase of investments	(23,486)	(32,577)	(48,451)
Redemption of investments	24,676	51,410	4,802
Purchase of property and equipment	(2,381)	(1,452)	(2,815)
Proceeds from sale of equipment	22
Purchased and capitalized intangible assets	(45)	(803)	(1,194)
Net cash (used in) provided by investing activities	(1,214)	16,578	(47,658)
Cash flows from financing activities:
Payment of debt		(23,000)	(2,000)
Payment of capital leases	(13)
Proceeds from exercise of common stock options	714	1,160	1,190
Net cash (used in) provided by financing activities	701	(21,840)	(810)
Net decrease in cash and cash equivalents	(5,917)	(10,089)	(50,318)
Cash and cash equivalents at beginning of period	11,676	21,765	72,083
Cash and cash equivalents at end of period	5,759	11,676	21,765
Supplemental disclosure of cash flow information:
Cash paid for interest	9	652	666
Cash paid for income taxes, net of refunds received	6	5	21
Noncash investing/operating activities:
Transfer of property and equipment to materials inventory	791	1,543	999
Transfer of materials inventory to property and equipment	1,515	3,373
Additions to property, equipment and intangible assets not paid at the end of the period	$ 84	$ 853	$ 360