Revenue (Schedule of Contract Liability) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Sep. 30, 2020
Contract With Customer Liability [Line Items]
Current contract liabilities	$ 28,760	$ 24,620
Noncurrent contract liabilities	376,806	366,642
Deferred Revenue From Material Rights From GE Joint Venture Formation [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities	4,419	4,066
Noncurrent contract liabilities	236,610	234,240
Deferred Revenue From Advance Invoicing And/Or Prepayments From Customers [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities	3,922	3,239
Noncurrent contract liabilities	716	85
Liability Related To Customer Supplied Inventory [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities	15,790	14,955
Deferred Revenue From Material Rights Related To Engineering And Development Funding [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities	4,629	2,360
Noncurrent contract liabilities	$ 139,480	$ 132,317