Revenue (Schedule of Contract Liability) (Details) - USD ($) $ in Thousands		Jun. 30, 2019	Sep. 30, 2018
Contract With Customer Liability [Line Items]
Current contract liabilities		$ 26,307	$ 9,659
Noncurrent contract liabilities	[1]	332,927	235,300
Deferred Revenue From Material Rights From GE Joint Venture Formation [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities		6,806	7,087
Noncurrent contract liabilities		234,038	235,300
Deferred Revenue From Advance Invoicing And/Or Prepayments From Customers [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities		3,343	$ 2,572
Liability Related To Customer Supplied Inventory [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities		13,021
Deferred Revenue From Material Rights Related To Engineering And Development Funding [Member]
Contract With Customer Liability [Line Items]
Current contract liabilities		3,137
Noncurrent contract liabilities		$ 98,889

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