Revenue (Schedule of Contract Liability) (Details) - USD ($) $ in Thousands		Sep. 30, 2019	Sep. 30, 2018
Contract With Customer Liability [Line Items]
Current contract liabilities		$ 27,891	$ 9,659
Noncurrent contract liabilities	[1]	337,165	235,300
Deferred Revenue From Material Rights From GE Joint Venture Formation [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities		8,317	7,087
Noncurrent contract liabilities		230,588	235,300
Deferred Revenue From Advance Invoicing And/Or Prepayments From Customers [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities		4,554	$ 2,572
Noncurrent contract liabilities		141
Liability Related To Customer Supplied Inventory [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities		13,396
Deferred Revenue From Material Rights Related To Engineering And Development Funding [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities		1,624
Noncurrent contract liabilities		$ 106,436

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