REVENUES - Disaggregation of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of revenues
Total revenues	$ 162,949	$ 171,728
Point in time
Disaggregation of revenues
Total revenues	78,181
Over time
Disaggregation of revenues
Total revenues	84,768
United States
Disaggregation of revenues
Total revenues	118,124
International
Disaggregation of revenues
Total revenues	44,825
Commercial
Disaggregation of revenues
Total revenues	118,465
U.S. Government
Disaggregation of revenues
Total revenues	44,484
Aerospace & Defense
Disaggregation of revenues
Total revenues	66,891	77,511
Aerospace & Defense | Point in time
Disaggregation of revenues
Total revenues	26,946
Aerospace & Defense | Over time
Disaggregation of revenues
Total revenues	39,945
Aerospace & Defense | United States
Disaggregation of revenues
Total revenues	57,813
Aerospace & Defense | International
Disaggregation of revenues
Total revenues	9,078
Aerospace & Defense | Commercial
Disaggregation of revenues
Total revenues	27,879
Aerospace & Defense | U.S. Government
Disaggregation of revenues
Total revenues	39,012
USG
Disaggregation of revenues
Total revenues	54,540	52,834
USG | Point in time
Disaggregation of revenues
Total revenues	42,367
USG | Over time
Disaggregation of revenues
Total revenues	12,173
USG | United States
Disaggregation of revenues
Total revenues	37,045
USG | International
Disaggregation of revenues
Total revenues	17,495
USG | Commercial
Disaggregation of revenues
Total revenues	53,864
USG | U.S. Government
Disaggregation of revenues
Total revenues	676
Test
Disaggregation of revenues
Total revenues	41,518	$ 41,383
Test | Point in time
Disaggregation of revenues
Total revenues	8,868
Test | Over time
Disaggregation of revenues
Total revenues	32,650
Test | United States
Disaggregation of revenues
Total revenues	23,266
Test | International
Disaggregation of revenues
Total revenues	18,252
Test | Commercial
Disaggregation of revenues
Total revenues	36,722
Test | U.S. Government
Disaggregation of revenues
Total revenues	$ 4,796