Revenues - Disaggregation of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of revenues
Total revenues	$ 208,030	$ 172,665	$ 180,492	$ 171,728	$ 213,177	$ 178,259	$ 171,243	$ 163,365	$ 732,915	$ 726,044	$ 683,650
Point in time
Disaggregation of revenues
Total revenues									338,076
Over time
Disaggregation of revenues
Total revenues									394,839
United States
Disaggregation of revenues
Total revenues									531,861	537,200	495,800
International
Disaggregation of revenues
Total revenues									201,054
Commercial
Disaggregation of revenues
Total revenues									512,810
Government
Disaggregation of revenues
Total revenues									220,105
Aerospace & Defense
Disaggregation of revenues
Total revenues									354,320	325,700	286,800
Aerospace & Defense | Point in time
Disaggregation of revenues
Total revenues									160,402
Aerospace & Defense | Over time
Disaggregation of revenues
Total revenues									193,918
Aerospace & Defense | United States
Disaggregation of revenues
Total revenues									305,155
Aerospace & Defense | International
Disaggregation of revenues
Total revenues									49,165
Aerospace & Defense | Commercial
Disaggregation of revenues
Total revenues									169,484
Aerospace & Defense | Government
Disaggregation of revenues
Total revenues									184,836
USG
Disaggregation of revenues
Total revenues									191,703	211,900	214,000
USG | Point in time
Disaggregation of revenues
Total revenues									144,192
USG | Over time
Disaggregation of revenues
Total revenues									47,511
USG | United States
Disaggregation of revenues
Total revenues									134,601
USG | International
Disaggregation of revenues
Total revenues									57,102
USG | Commercial
Disaggregation of revenues
Total revenues									184,906
USG | Government
Disaggregation of revenues
Total revenues									6,797
Test
Disaggregation of revenues
Total revenues									186,892	$ 188,400	$ 182,900
Test | Point in time
Disaggregation of revenues
Total revenues									33,482
Test | Over time
Disaggregation of revenues
Total revenues									153,410
Test | United States
Disaggregation of revenues
Total revenues									92,105
Test | International
Disaggregation of revenues
Total revenues									94,787
Test | Commercial
Disaggregation of revenues
Total revenues									158,420
Test | Government
Disaggregation of revenues
Total revenues									$ 28,472