REVENUES - Disaggregation of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of revenues
Total revenues	$ 171,728	$ 163,365
Point in time
Disaggregation of revenues
Total revenues	83,687
Over time
Disaggregation of revenues
Total revenues	88,041
United States
Disaggregation of revenues
Total revenues	124,194
International
Disaggregation of revenues
Total revenues	47,534
Commercial
Disaggregation of revenues
Total revenues	129,391
U.S. Government
Disaggregation of revenues
Total revenues	42,337
Aerospace & Defense
Disaggregation of revenues
Total revenues	77,511	66,224
Aerospace & Defense | Point in time
Disaggregation of revenues
Total revenues	35,761
Aerospace & Defense | Over time
Disaggregation of revenues
Total revenues	41,750
Aerospace & Defense | United States
Disaggregation of revenues
Total revenues	64,706
Aerospace & Defense | International
Disaggregation of revenues
Total revenues	12,805
Aerospace & Defense | Commercial
Disaggregation of revenues
Total revenues	41,907
Aerospace & Defense | U.S. Government
Disaggregation of revenues
Total revenues	35,604
Test
Disaggregation of revenues
Total revenues	41,383	41,286
Test | Point in time
Disaggregation of revenues
Total revenues	7,611
Test | Over time
Disaggregation of revenues
Total revenues	33,772
Test | United States
Disaggregation of revenues
Total revenues	24,837
Test | International
Disaggregation of revenues
Total revenues	16,546
Test | Commercial
Disaggregation of revenues
Total revenues	35,249
Test | U.S. Government
Disaggregation of revenues
Total revenues	6,134
USG
Disaggregation of revenues
Total revenues	52,834	$ 55,855
USG | Point in time
Disaggregation of revenues
Total revenues	40,315
USG | Over time
Disaggregation of revenues
Total revenues	12,519
USG | United States
Disaggregation of revenues
Total revenues	34,651
USG | International
Disaggregation of revenues
Total revenues	18,183
USG | Commercial
Disaggregation of revenues
Total revenues	52,235
USG | U.S. Government
Disaggregation of revenues
Total revenues	$ 599