Summary of Significant Accounting Policies - Narrative (Details) shares in Thousands	3 Months Ended			6 Months Ended		12 Months Ended
	Dec. 31, 2017 USD ($) shares	Sep. 30, 2017	Dec. 31, 2016 USD ($) shares	Dec. 31, 2017 USD ($) Segment shares	Dec. 31, 2016 USD ($) shares	Jun. 30, 2018	Jun. 30, 2017 USD ($)
Summary Of Significant Accounting Policies
Foreign currency transaction gain (loss), realized	$ (100,000)		$ (300,000)	$ (8,000)	$ (400,000)
Derivative instruments, gain (loss) realized in income, net	(100,000)		200,000	(100,000)	100,000
Bad debt expenses	0		0	0	0
Inventory valuation reserves	$ 1,400,000			$ 1,400,000			$ 900,000
Money back guarantee period				30 days
Percentage of products can be returned for a full refund by terminated distributors (up to)	30.00%			30.00%
Percent of restocking fee	10.00%			10.00%
Reserve for sales returns	$ 300,000			$ 300,000			400,000
Research and development	300,000		300,000	500,000	600,000
Income tax expenses	$ 1,738,000		$ 129,000	$ 2,179,000	$ 627,000
Effective tax rate		35.10%		65.80%
Deferred tax asset reduction				$ 1,200,000
Increase in effective tax rate				35.20%
Antidilutive securities excluded from EPS calculation (in shares) | shares	100		100	300	43
Number of operating segments | Segment				1
Number of geographic segments | Segment				2
United States
Summary Of Significant Accounting Policies
Long-lived assets	$ 8,000,000			$ 8,000,000			6,200,000
Japan
Summary Of Significant Accounting Policies
Long-lived assets	$ 900,000			900,000			$ 900,000
Cash accounts held primarily at One Financial Institution
Summary Of Significant Accounting Policies
Concentration of credit risk				9,500,000
Cash held primarily at Other Financial Institutions
Summary Of Significant Accounting Policies
Concentration of credit risk				$ 3,300,000
Forecast
Summary Of Significant Accounting Policies
Statutory tax blended rate						28.00%