DISCONTINUED OPERATIONS - Narrative (Details) $ in Thousands	12 Months Ended			24 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($) position	Sep. 30, 2019 USD ($)	Sep. 30, 2021 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue from disposed business	$ 271,060	$ 340,976	$ 335,041
Discontinued Operations | Installation Services and Other Discontinued Activities
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue from disposed business	0	0	0
Discontinued operation, claims dispute settlement			11,050
Discontinued operation, claims dispute settlement, net of tax			8,335
Total Liabilities Held for Sale	7,074	$ 10,811		$ 7,074
Discontinued Operations | Defense Electronics | Voluntary Employee Retirement Plan and Reduction In Force
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of headcount reduced | position		90
Discontinued Operations | Defense Electronics | Voluntary Employee Retirement Plan
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Restructuring charges	2,200	$ 2,100		$ 4,300
Discontinued Operations | Defense Electronics | Exit of Older Weather Radar Product Lines
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business exit costs	5,601
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations | Systems Engineering Group, Inc.
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue from disposed business	$ 6,713	$ 31,758	$ 27,450