Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash flows from operating activities:
Net loss	$ (6,201)	$ (6,883)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	836	884
Write-off of abandoned patents	374	50
Loss on sale of property and equipment	0	2
Compensation expense related to stock options and awards	804	1,534
Purchase of technology license with common stock	0	775
Changes in operating assets and liabilities:
Receivables and other assets	(1,902)	(1,403)
Accounts payable and accrued expenses	65	(1,885)
Deferred revenue	(138)	2,110
Deferred rent	(416)	(313)
Net cash used in operating activities	(6,578)	(5,129)
Cash flows from investing activities:
Maturities of marketable securities	19,215	15,030
Purchases of marketable securities	(25,143)	(11,500)
Purchases of property and equipment	(230)	(58)
Patent expenditures	0	(53)
Net cash (used in) provided by investing activities	(6,158)	3,419
Cash flows from financing activities:
Net proceeds from issuance of common stock	7,759	3
Payment of withholding taxes for net settlement of restricted stock units	(13)	(23)
Net cash provided by (used in) financing activities	7,746	(20)
Net decrease in cash and cash equivalents	(4,990)	(1,730)
Cash and cash equivalents at beginning of period	13,450	20,471
Cash and cash equivalents at end of period	$ 8,460	$ 18,741