Acquisitions (Narrative) (Details)					12 Months Ended
	Aug. 01, 2019 USD ($)	Jul. 31, 2019 USD ($)	Apr. 29, 2019 USD ($) employee	Feb. 28, 2019 USD ($) $ / shares shares	Jul. 31, 2019
Business Acquisition [Line Items]
Contract period to develop, implement and operate emergency communications system					5 years
Solacom
Business Acquisition [Line Items]
Aggregate purchase price		$ 32,934,000		$ 32,934,000
Aggregate purchase price - settled in cash		27,328,000		27,328,000
Aggregate purchase price - settled with issuance of common stock		5,606,000		$ 5,606,000
Aggregate purchase price - settled with issuance of common stock (in shares) | shares				208,669
Weighted average stock price (in dollars per share) | $ / shares				$ 26.86
Consideration transferred, net of cash acquired				$ 31,489,000
Cash acquired from acquisition				$ 1,445,000
GD NG-911 business
Business Acquisition [Line Items]
Aggregate purchase price		$ 10,000,000	$ 10,000,000
Number of employees hired | employee			60
Amortization period of other liabilities			5 years 3 months
Goodwill amount estimated to be tax deductible			$ 7,300,000
Subsequent Event | GD NG-911 business
Business Acquisition [Line Items]
Proposed upward adjustment	$ 2,900,000
Proposed reduction to the purchase price	$ 890,000