Revenue (Schedule of Contract Liability) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020
Contract With Customer Liability [Line Items]
Current contract liabilities	$ 29,385	$ 24,620
Noncurrent contract liabilities	371,024	366,642
Deferred Revenue From Material Rights From GE Joint Venture Formation [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities	4,242	4,066
Noncurrent contract liabilities	232,882	234,240
Deferred Revenue From Advance Invoicing And/Or Prepayments From Customers [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities	4,182	3,239
Noncurrent contract liabilities	1,338	85
Liability Related To Customer Supplied Inventory [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities	16,885	14,955
Deferred Revenue From Material Rights Related To Engineering And Development Funding [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities	4,076	2,360
Noncurrent contract liabilities	$ 136,804	$ 132,317