Operating Segments - Product Category (Details) - USD ($)	3 Months Ended								12 Months Ended
	Mar. 31, 2019	Dec. 30, 2018	Sep. 30, 2018	Jul. 01, 2018	Apr. 01, 2018	Dec. 24, 2017	Sep. 24, 2017	Jun. 25, 2017	Mar. 31, 2019	Apr. 01, 2018	Mar. 26, 2017
Revenue and Gross Profit from External Customers
Revenues	$ 144,963,800	$ 152,294,500	$ 158,636,100	$ 150,919,400	$ 148,920,100	$ 146,260,300	$ 145,083,500	$ 140,010,800	$ 606,813,800	$ 580,274,700	$ 533,295,100
Gross Profit	$ 28,267,200	$ 30,998,700	$ 31,394,700	$ 30,698,100	$ 31,538,700	$ 29,599,800	$ 29,923,100	$ 29,166,800	121,358,700	120,228,400	111,767,800
Base station infrastructure
Revenue and Gross Profit from External Customers
Revenues									292,787,000	248,949,000	209,869,000
Gross Profit									61,458,000	58,015,000	54,280,000
Network systems
Revenue and Gross Profit from External Customers
Revenues									86,555,000	98,642,000	87,222,000
Gross Profit									13,604,000	14,649,000	11,897,000
Installation, test and maintenance
Revenue and Gross Profit from External Customers
Revenues									32,595,000	33,200,000	31,851,000
Gross Profit									6,433,000	6,266,000	5,921,000
Mobile device accessories
Revenue and Gross Profit from External Customers
Revenues									194,877,000	199,484,000	204,353,000
Gross Profit									$ 39,864,000	$ 41,298,000	$ 39,670,000