Revenue (Schedule of Contract Liability) (Details) - USD ($) $ in Thousands		Mar. 31, 2020	Sep. 30, 2019
Contract With Customer Liability [Line Items]
Current contract liabilities		$ 25,601	$ 27,891
Noncurrent contract liabilities	[1]	352,440	337,165
Deferred Revenue From Material Rights From GE Joint Venture Formation [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities		4,712	8,317
Noncurrent contract liabilities		235,558	230,588
Deferred Revenue From Advance Invoicing And/Or Prepayments From Customers [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities		4,572	4,554
Noncurrent contract liabilities		129	141
Liability Related To Customer Supplied Inventory [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities		13,884	13,396
Deferred Revenue From Material Rights Related To Engineering And Development Funding [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities		2,433	1,624
Noncurrent contract liabilities		$ 116,753	$ 106,436

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