Revenue (Schedule of Contract Liability) (Details) - USD ($) $ in Thousands		Sep. 30, 2020	Sep. 30, 2019
Contract With Customer Liability [Line Items]
Current contract liabilities		$ 24,620	$ 27,891
Noncurrent contract liabilities	[1]	366,642	337,165
Deferred Revenue From Material Rights From GE Joint Venture Formation [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities		4,066	8,317
Noncurrent contract liabilities		234,240	230,588
Deferred Revenue From Advance Invoicing And/Or Prepayments From Customers [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities		3,239	4,554
Noncurrent contract liabilities		85	141
Liability Related To Customer Supplied Inventory [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities		14,955	13,396
Deferred Revenue From Material Rights Related To Engineering And Development Funding [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities		2,360	1,624
Noncurrent contract liabilities		$ 132,317	$ 106,436

[1] See Note 3, Revenue, for more information on net noncurrent contract liabilities.