Debt Financing (Details)			6 Months Ended
	Jun. 29, 2018 CNY (¥)	Jan. 10, 2018 USD ($)	Jun. 30, 2018 USD ($)	Sep. 01, 2018 USD ($)	Jun. 29, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jun. 16, 2017 USD ($)
Line of Credit Facility [Line Items]
Restricted cash			$ 6,520,000			$ 1,020,000	$ 1,020,000
Domestic Line of Credit
Line of Credit Facility [Line Items]
Letters of credit, amount outstanding			$ 4,936,000			3,004,000
Line of credit, commitment fee percentage			0.25%
Line of credit, remaining borrowing capacity			$ 564,000			1,996,000
China Facility
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity	¥ 5,250,000.000				$ 793,000
Restricted cash			1,020,000
Line of credit, amount outstanding			0
China Facility | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate (as percent)	140.00%
Standby Letters of Credit
Line of Credit Facility [Line Items]
Letters of credit, amount outstanding			167,000			246,000
Line of credit, remaining borrowing capacity			626,000			753,000
Amended Amount
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity								$ 5,000,000
Letters of credit, amount outstanding			$ 0			$ 0
Amendment 2018 | Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity		$ 5,500,000
Increase in credit facility		$ 500,000
Forecast | Amendment 2018 | Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity				$ 5,000,000