Revenues - Disaggregation of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of revenues
Net sales	$ 236,658	$ 199,766	$ 193,949	$ 182,597	$ 231,086	$ 192,223	$ 174,778	$ 173,495	$ 812,970	$ 771,582	$ 685,740
Point in time
Disaggregation of revenues
Net sales									365,137
Over time
Disaggregation of revenues
Net sales									447,833
United States
Disaggregation of revenues
Net sales									582,972	536,700	503,100
International
Disaggregation of revenues
Net sales									229,998
Commercial
Disaggregation of revenues
Net sales									642,822
Government
Disaggregation of revenues
Net sales									170,148
Filtration
Disaggregation of revenues
Net sales									325,735	286,800	279,500
Filtration | Point in time
Disaggregation of revenues
Net sales									164,224
Filtration | Over time
Disaggregation of revenues
Net sales									161,511
Filtration | United States
Disaggregation of revenues
Net sales									274,446
Filtration | International
Disaggregation of revenues
Net sales									51,289
Filtration | Commercial
Disaggregation of revenues
Net sales									180,356
Filtration | Government
Disaggregation of revenues
Net sales									145,379
USG
Disaggregation of revenues
Net sales									211,915	214,000	162,400
USG | Point in time
Disaggregation of revenues
Net sales									164,126
USG | Over time
Disaggregation of revenues
Net sales									47,789
USG | United States
Disaggregation of revenues
Net sales									150,381
USG | International
Disaggregation of revenues
Net sales									61,534
USG | Commercial
Disaggregation of revenues
Net sales									207,666
USG | Government
Disaggregation of revenues
Net sales									4,249
Test
Disaggregation of revenues
Net sales									188,394	182,900	160,900
Test | Point in time
Disaggregation of revenues
Net sales									36,787
Test | Over time
Disaggregation of revenues
Net sales									151,607
Test | United States
Disaggregation of revenues
Net sales									112,358
Test | International
Disaggregation of revenues
Net sales									76,036
Test | Commercial
Disaggregation of revenues
Net sales									168,201
Test | Government
Disaggregation of revenues
Net sales									20,193
Technical Packaging
Disaggregation of revenues
Net sales									86,926	$ 87,900	$ 82,900
Technical Packaging | Point in time
Disaggregation of revenues
Net sales									0
Technical Packaging | Over time
Disaggregation of revenues
Net sales									86,926
Technical Packaging | United States
Disaggregation of revenues
Net sales									45,787
Technical Packaging | International
Disaggregation of revenues
Net sales									41,139
Technical Packaging | Commercial
Disaggregation of revenues
Net sales									86,599
Technical Packaging | Government
Disaggregation of revenues
Net sales									$ 327