REVENUES - Disaggregation of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of revenues
Net sales	$ 181,394	$ 172,665	$ 509,962	$ 524,885
Point in time
Disaggregation of revenues
Net sales	82,428	73,364	236,454	245,106
Over time
Disaggregation of revenues
Net sales	98,966	99,301	273,508	279,779
United States
Disaggregation of revenues
Net sales	135,531	119,416	376,078	379,194
International
Disaggregation of revenues
Net sales	45,863	53,249	133,884	145,691
Commercial
Disaggregation of revenues
Net sales	123,506	115,962	352,950	374,459
U.S. Government
Disaggregation of revenues
Net sales	57,888	56,703	157,012	150,426
Aerospace & Defense
Disaggregation of revenues
Net sales	85,576	84,072	234,720	256,707
Aerospace & Defense | Point in time
Disaggregation of revenues
Net sales	37,513	36,461	103,492	118,660
Aerospace & Defense | Over time
Disaggregation of revenues
Net sales	48,063	47,611	131,228	138,047
Aerospace & Defense | United States
Disaggregation of revenues
Net sales	75,701	73,476	205,527	219,640
Aerospace & Defense | International
Disaggregation of revenues
Net sales	9,875	10,596	29,193	37,067
Aerospace & Defense | Commercial
Disaggregation of revenues
Net sales	34,708	37,485	95,712	130,817
Aerospace & Defense | U.S. Government
Disaggregation of revenues
Net sales	50,868	46,587	139,008	125,890
USG
Disaggregation of revenues
Net sales	47,704	42,577	141,799	139,179
USG | Point in time
Disaggregation of revenues
Net sales	35,242	27,765	105,173	100,289
USG | Over time
Disaggregation of revenues
Net sales	12,462	14,812	36,626	38,890
USG | United States
Disaggregation of revenues
Net sales	32,111	26,499	96,601	90,155
USG | International
Disaggregation of revenues
Net sales	15,593	16,078	45,198	49,024
USG | Commercial
Disaggregation of revenues
Net sales	46,735	39,740	139,149	135,711
USG | U.S. Government
Disaggregation of revenues
Net sales	969	2,837	2,650	3,468
Test
Disaggregation of revenues
Net sales	48,114	46,016	133,443	128,999
Test | Point in time
Disaggregation of revenues
Net sales	9,673	9,138	27,789	26,157
Test | Over time
Disaggregation of revenues
Net sales	38,441	36,878	105,654	102,842
Test | United States
Disaggregation of revenues
Net sales	27,719	19,441	73,950	69,399
Test | International
Disaggregation of revenues
Net sales	20,395	26,575	59,493	59,600
Test | Commercial
Disaggregation of revenues
Net sales	42,063	38,737	118,089	107,931
Test | U.S. Government
Disaggregation of revenues
Net sales	$ 6,051	$ 7,279	$ 15,354	$ 21,068