Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Revenues	$ 22,974	$ 28,235	$ 39,507
Cost of revenues	5,082	7,564	8,152
Gross profit	17,892	20,671	31,355
Operating expenses:
Selling and marketing	6,186	9,615	8,902
Research and development	8,952	15,906	13,863
General and administrative	8,551	10,341	11,128
Restructuring expenses	(123)	303
Long-lived asset impairment		411
Total operating expenses	23,566	36,576	33,893
Operating loss	(5,674)	(15,905)	(2,538)
Non-operating income (expense):
Change in carrying value of contingent liability		668
Loss on debt extinguishment	(405)
Interest income (expense), net	(1,120)	(313)	1
Other income (expense), net	(8)	(22)	3
Loss before provision for income taxes	(7,207)	(15,572)	(2,534)
Provision for income tax expense (benefit)	(546)	(229)	68
Net loss	(6,661)	(15,343)	(2,602)
Other comprehensive income (loss), before tax:
Unrealized holding gains (losses) on available-for-sale securities		2	(1)
Other comprehensive income (expense), net of tax		2	(1)
Comprehensive loss	$ (6,661)	$ (15,341)	$ (2,603)
Net loss per share:
Basic and diluted	$ (0.49)	$ (1.28)	$ (0.26)
Weighted average shares outstanding:
Basic and diluted	13,489	11,951	10,162