2. Revenue: Schedule of geographical revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Application total
Product Application	$ 5,702	$ 12,200	$ 20,873	$ 28,653
Transferred at Point in Time
Product Application	749	472	2,151	2,031
Transferred over Time
Product Application	4,953	11,728	18,722	26,622
Audio-Visual Systems
Product Application	2,878	9,078	12,782	17,485
Domes
Product Application	1,722	2,226	4,518	7,804
Show Content
Product Application	448	382	1,649	1,552
Maintenance and Service
Product Application	654	514	1,924	1,812
Planetarium Theaters | Application total
Product Application	5,209	11,456	18,531	24,802
Planetarium Theaters | Transferred at Point in Time
Product Application	749	472	2,078	2,031
Planetarium Theaters | Transferred over Time
Product Application	4,460	10,984	16,453	22,771
Planetarium Theaters | Audio-Visual Systems
Product Application	2,854	8,718	11,978	16,713
Planetarium Theaters | Domes
Product Application	1,256	1,842	3,056	4,725
Planetarium Theaters | Show Content
Product Application	448	382	1,576	1,552
Planetarium Theaters | Maintenance and Service
Product Application	651	514	1,921	1,812
Other Visitor Attractions | Application total
Product Application	493	626	2,217	3,104
Other Visitor Attractions | Transferred at Point in Time
Product Application	0	0	73	0
Other Visitor Attractions | Transferred over Time
Product Application	493	626	2,144	3,104
Other Visitor Attractions | Audio-Visual Systems
Product Application	24	360	804	772
Other Visitor Attractions | Domes
Product Application	466	266	1,337	2,332
Other Visitor Attractions | Show Content
Product Application	0	0	73	0
Other Visitor Attractions | Maintenance and Service
Product Application	3	0	3	0
Architectural Treatments | Application total
Product Application	0	118	125	747
Architectural Treatments | Transferred at Point in Time
Product Application	0	0	0	0
Architectural Treatments | Transferred over Time
Product Application	0	118	125	747
Architectural Treatments | Audio-Visual Systems
Product Application	0	0	0	0
Architectural Treatments | Domes
Product Application	0	118	125	747
Architectural Treatments | Show Content
Product Application	0	0	0	0
Architectural Treatments | Maintenance and Service
Product Application	0	0	0	0
North America
Product Application	2,880	7,557	11,062	17,563
North America | Planetarium Theaters
Product Application	2,529	7,545	10,118	16,449
North America | Other Visitor Attractions
Product Application	351	12	819	485
North America | Architectural Treatments
Product Application	0	0	125	629
Europe
Product Application	771	3,403	5,154	5,246
Europe | Planetarium Theaters
Product Application	747	2,853	3,912	4,284
Europe | Other Visitor Attractions
Product Application	24	432	1,242	844
Europe | Architectural Treatments
Product Application	0	118	0	118
Asia
Product Application	1,213	869	2,463	5,141
Asia | Planetarium Theaters
Product Application	1,095	687	2,307	3,366
Asia | Other Visitor Attractions
Product Application	118	182	156	1,775
Asia | Architectural Treatments
Product Application	0	0	0	0
Other
Product Application	838	371	2,194	703
Other | Planetarium Theaters
Product Application	838	371	2,194	703
Other | Other Visitor Attractions
Product Application	0	0	0	0
Other | Architectural Treatments
Product Application	$ 0	$ 0	$ 0	$ 0