Revenues from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Revenue from Contracts with Customers
Net revenues	$ 127,474	$ 110,206	$ 234,543	$ 199,899
Product
Revenue from Contracts with Customers
Net revenues	121,262	104,660	223,157	187,514
Aerospace
Revenue from Contracts with Customers
Net revenues	68,858	59,033	123,465	105,872
Chemical processing
Revenue from Contracts with Customers
Net revenues	21,761	21,148	40,681	34,504
Industrial gas turbine
Revenue from Contracts with Customers
Net revenues	13,685	11,755	27,768	25,176
Other markets
Revenue from Contracts with Customers
Net revenues	16,958	12,724	31,243	21,962
Other
Revenue from Contracts with Customers
Net revenues	$ 6,212	$ 5,546	$ 11,386	$ 12,385