2. Revenue: Schedule of geographical revenues (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 28, 2019	Jun. 29, 2018	Jun. 28, 2019	Jun. 29, 2018
Transferred at Point in Time
Product Application	$ 586	$ 1,078	$ 1,402	$ 1,559
Transferred over Time
Product Application	7,420	7,794	13,769	14,894
Planetarium Theaters | Transferred at Point in Time
Product Application	513	1,078	1,329	1,559
Planetarium Theaters | Transferred over Time
Product Application	6,289	6,025	11,993	11,787
Other Visitor Attractions | Transferred at Point in Time
Product Application	73	0	73	0
Other Visitor Attractions | Transferred over Time
Product Application	1,082	1,500	1,651	2,478
Architectural Treatments | Transferred at Point in Time
Product Application	0	0	0	0
Architectural Treatments | Transferred over Time
Product Application	49	269	125	629
North America
Product Application	3,712	6,393	8,182	10,006
North America | Planetarium Theaters
Product Application	3,410	5,771	7,589	8,904
North America | Other Visitor Attractions
Product Application	253	353	468	473
North America | Architectural Treatments
Product Application	49	269	125	629
Europe
Product Application	2,694	1,499	4,383	1,843
Europe | Planetarium Theaters
Product Application	1,792	1,098	3,165	1,431
Europe | Other Visitor Attractions
Product Application	902	401	1,218	412
Europe | Architectural Treatments
Product Application	0	0	0	0
Asia
Product Application	727	969	1,250	4,272
Asia | Planetarium Theaters
Product Application	727	223	1,212	2,679
Asia | Other Visitor Attractions
Product Application	0	746	38	1,593
Asia | Architectural Treatments
Product Application	0	0	0	0
Other
Product Application	873	11	1,356	332
Other | Planetarium Theaters
Product Application	873	11	1,356	332
Other | Other Visitor Attractions
Product Application	0	0	0	0
Other | Architectural Treatments
Product Application	0	0	0	0
Application total
Product Application	8,006	8,872	15,171	16,453
Application total | Planetarium Theaters
Product Application	6,802	7,103	13,322	13,346
Application total | Other Visitor Attractions
Product Application	1,155	1,500	1,724	2,478
Application total | Architectural Treatments
Product Application	49	269	125	629
Audio-Visual Systems
Product Application	5,357	4,410	9,904	8,407
Audio-Visual Systems | Planetarium Theaters
Product Application	4,728	4,009	9,124	7,995
Audio-Visual Systems | Other Visitor Attractions
Product Application	629	401	780	412
Audio-Visual Systems | Architectural Treatments
Product Application	0	0	0	0
Domes
Product Application	1,501	2,876	2,796	5,578
Domes | Planetarium Theaters
Product Application	999	1,508	1,800	2,883
Domes | Other Visitor Attractions
Product Application	453	1,099	871	2,066
Domes | Architectural Treatments
Product Application	49	269	125	629
Show Content
Product Application	430	844	1,201	1,170
Show Content | Planetarium Theaters
Product Application	357	844	1,128	1,170
Show Content | Other Visitor Attractions
Product Application	73	0	73	0
Show Content | Architectural Treatments
Product Application	0	0	0	0
Maintenance and Service
Product Application	718	742	1,270	1,298
Maintenance and Service | Planetarium Theaters
Product Application	718	742	1,270	1,298
Maintenance and Service | Other Visitor Attractions
Product Application	0	0	0	0
Maintenance and Service | Architectural Treatments
Product Application	$ 0	$ 0	$ 0	$ 0